--- /dev/null
+From stable+bounces-27531-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:35 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:25 -0700
+Subject: Documentation/hw-vuln: Add documentation for RFDS
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Josh Poimboeuf <jpoimboe@kernel.org>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-9-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 4e42765d1be01111df0c0275bbaf1db1acef346e upstream.
+
+Add the documentation for transient execution vulnerability Register
+File Data Sampling (RFDS) that affects Intel Atom CPUs.
+
+ [ pawan: s/ATOM_GRACEMONT/ALDERLAKE_N/ ]
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
+Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ Documentation/admin-guide/hw-vuln/index.rst | 1
+ Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst | 104 +++++++++++
+ 2 files changed, 105 insertions(+)
+
+--- a/Documentation/admin-guide/hw-vuln/index.rst
++++ b/Documentation/admin-guide/hw-vuln/index.rst
+@@ -21,3 +21,4 @@ are configurable at compile, boot or run
+ cross-thread-rsb.rst
+ gather_data_sampling.rst
+ srso
++ reg-file-data-sampling
+--- /dev/null
++++ b/Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
+@@ -0,0 +1,104 @@
++==================================
++Register File Data Sampling (RFDS)
++==================================
++
++Register File Data Sampling (RFDS) is a microarchitectural vulnerability that
++only affects Intel Atom parts(also branded as E-cores). RFDS may allow
++a malicious actor to infer data values previously used in floating point
++registers, vector registers, or integer registers. RFDS does not provide the
++ability to choose which data is inferred. CVE-2023-28746 is assigned to RFDS.
++
++Affected Processors
++===================
++Below is the list of affected Intel processors [#f1]_:
++
++ =================== ============
++ Common name Family_Model
++ =================== ============
++ ATOM_GOLDMONT 06_5CH
++ ATOM_GOLDMONT_D 06_5FH
++ ATOM_GOLDMONT_PLUS 06_7AH
++ ATOM_TREMONT_D 06_86H
++ ATOM_TREMONT 06_96H
++ ALDERLAKE 06_97H
++ ALDERLAKE_L 06_9AH
++ ATOM_TREMONT_L 06_9CH
++ RAPTORLAKE 06_B7H
++ RAPTORLAKE_P 06_BAH
++ ALDERLAKE_N 06_BEH
++ RAPTORLAKE_S 06_BFH
++ =================== ============
++
++As an exception to this table, Intel Xeon E family parts ALDERLAKE(06_97H) and
++RAPTORLAKE(06_B7H) codenamed Catlow are not affected. They are reported as
++vulnerable in Linux because they share the same family/model with an affected
++part. Unlike their affected counterparts, they do not enumerate RFDS_CLEAR or
++CPUID.HYBRID. This information could be used to distinguish between the
++affected and unaffected parts, but it is deemed not worth adding complexity as
++the reporting is fixed automatically when these parts enumerate RFDS_NO.
++
++Mitigation
++==========
++Intel released a microcode update that enables software to clear sensitive
++information using the VERW instruction. Like MDS, RFDS deploys the same
++mitigation strategy to force the CPU to clear the affected buffers before an
++attacker can extract the secrets. This is achieved by using the otherwise
++unused and obsolete VERW instruction in combination with a microcode update.
++The microcode clears the affected CPU buffers when the VERW instruction is
++executed.
++
++Mitigation points
++-----------------
++VERW is executed by the kernel before returning to user space, and by KVM
++before VMentry. None of the affected cores support SMT, so VERW is not required
++at C-state transitions.
++
++New bits in IA32_ARCH_CAPABILITIES
++----------------------------------
++Newer processors and microcode update on existing affected processors added new
++bits to IA32_ARCH_CAPABILITIES MSR. These bits can be used to enumerate
++vulnerability and mitigation capability:
++
++- Bit 27 - RFDS_NO - When set, processor is not affected by RFDS.
++- Bit 28 - RFDS_CLEAR - When set, processor is affected by RFDS, and has the
++ microcode that clears the affected buffers on VERW execution.
++
++Mitigation control on the kernel command line
++---------------------------------------------
++The kernel command line allows to control RFDS mitigation at boot time with the
++parameter "reg_file_data_sampling=". The valid arguments are:
++
++ ========== =================================================================
++ on If the CPU is vulnerable, enable mitigation; CPU buffer clearing
++ on exit to userspace and before entering a VM.
++ off Disables mitigation.
++ ========== =================================================================
++
++Mitigation default is selected by CONFIG_MITIGATION_RFDS.
++
++Mitigation status information
++-----------------------------
++The Linux kernel provides a sysfs interface to enumerate the current
++vulnerability status of the system: whether the system is vulnerable, and
++which mitigations are active. The relevant sysfs file is:
++
++ /sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
++
++The possible values in this file are:
++
++ .. list-table::
++
++ * - 'Not affected'
++ - The processor is not vulnerable
++ * - 'Vulnerable'
++ - The processor is vulnerable, but no mitigation enabled
++ * - 'Vulnerable: No microcode'
++ - The processor is vulnerable but microcode is not updated.
++ * - 'Mitigation: Clear Register File'
++ - The processor is vulnerable and the CPU buffer clearing mitigation is
++ enabled.
++
++References
++----------
++.. [#f1] Affected Processors
++ https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html
--- /dev/null
+From stable+bounces-27529-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:23 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:14 -0700
+Subject: KVM/VMX: Move VERW closer to VMentry for MDS mitigation
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>, Sean Christopherson <seanjc@google.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-7-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 43fb862de8f628c5db5e96831c915b9aebf62d33 upstream.
+
+During VMentry VERW is executed to mitigate MDS. After VERW, any memory
+access like register push onto stack may put host data in MDS affected
+CPU buffers. A guest can then use MDS to sample host data.
+
+Although likelihood of secrets surviving in registers at current VERW
+callsite is less, but it can't be ruled out. Harden the MDS mitigation
+by moving the VERW mitigation late in VMentry path.
+
+Note that VERW for MMIO Stale Data mitigation is unchanged because of
+the complexity of per-guest conditional VERW which is not easy to handle
+that late in asm with no GPRs available. If the CPU is also affected by
+MDS, VERW is unconditionally executed late in asm regardless of guest
+having MMIO access.
+
+ [ pawan: conflict resolved in backport ]
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Acked-by: Sean Christopherson <seanjc@google.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-6-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kvm/vmx/vmenter.S | 3 +++
+ arch/x86/kvm/vmx/vmx.c | 12 ++++++++----
+ 2 files changed, 11 insertions(+), 4 deletions(-)
+
+--- a/arch/x86/kvm/vmx/vmenter.S
++++ b/arch/x86/kvm/vmx/vmenter.S
+@@ -99,6 +99,9 @@ SYM_FUNC_START(__vmx_vcpu_run)
+ /* Load guest RAX. This kills the @regs pointer! */
+ mov VCPU_RAX(%_ASM_AX), %_ASM_AX
+
++ /* Clobbers EFLAGS.ZF */
++ CLEAR_CPU_BUFFERS
++
+ /* Check EFLAGS.CF from the VMX_RUN_VMRESUME bit test above. */
+ jnc .Lvmlaunch
+
+--- a/arch/x86/kvm/vmx/vmx.c
++++ b/arch/x86/kvm/vmx/vmx.c
+@@ -398,7 +398,8 @@ static __always_inline void vmx_enable_f
+
+ static void vmx_update_fb_clear_dis(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
+ {
+- vmx->disable_fb_clear = vmx_fb_clear_ctrl_available;
++ vmx->disable_fb_clear = !cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF) &&
++ vmx_fb_clear_ctrl_available;
+
+ /*
+ * If guest will not execute VERW, there is no need to set FB_CLEAR_DIS
+@@ -6747,11 +6748,14 @@ static noinstr void vmx_vcpu_enter_exit(
+ {
+ kvm_guest_enter_irqoff();
+
+- /* L1D Flush includes CPU buffer clear to mitigate MDS */
++ /*
++ * L1D Flush includes CPU buffer clear to mitigate MDS, but VERW
++ * mitigation for MDS is done late in VMentry and is still
++ * executed in spite of L1D Flush. This is because an extra VERW
++ * should not matter much after the big hammer L1D Flush.
++ */
+ if (static_branch_unlikely(&vmx_l1d_should_flush))
+ vmx_l1d_flush(vcpu);
+- else if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF))
+- mds_clear_cpu_buffers();
+ else if (static_branch_unlikely(&mmio_stale_data_clear) &&
+ kvm_arch_has_assigned_device(vcpu->kvm))
+ mds_clear_cpu_buffers();
--- /dev/null
+From stable+bounces-27528-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:13 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:08 -0700
+Subject: KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
+To: stable@vger.kernel.org
+Cc: Sean Christopherson <seanjc@google.com>, Dave Hansen <dave.hansen@linux.intel.com>, Nikolay Borisov <nik.borisov@suse.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-6-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Sean Christopherson <seanjc@google.com>
+
+commit 706a189dcf74d3b3f955e9384785e726ed6c7c80 upstream.
+
+Use EFLAGS.CF instead of EFLAGS.ZF to track whether to use VMRESUME versus
+VMLAUNCH. Freeing up EFLAGS.ZF will allow doing VERW, which clobbers ZF,
+for MDS mitigations as late as possible without needing to duplicate VERW
+for both paths.
+
+ [ pawan: resolved merge conflict in __vmx_vcpu_run in backport. ]
+
+Signed-off-by: Sean Christopherson <seanjc@google.com>
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-5-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kvm/vmx/run_flags.h | 7 +++++--
+ arch/x86/kvm/vmx/vmenter.S | 6 +++---
+ 2 files changed, 8 insertions(+), 5 deletions(-)
+
+--- a/arch/x86/kvm/vmx/run_flags.h
++++ b/arch/x86/kvm/vmx/run_flags.h
+@@ -2,7 +2,10 @@
+ #ifndef __KVM_X86_VMX_RUN_FLAGS_H
+ #define __KVM_X86_VMX_RUN_FLAGS_H
+
+-#define VMX_RUN_VMRESUME (1 << 0)
+-#define VMX_RUN_SAVE_SPEC_CTRL (1 << 1)
++#define VMX_RUN_VMRESUME_SHIFT 0
++#define VMX_RUN_SAVE_SPEC_CTRL_SHIFT 1
++
++#define VMX_RUN_VMRESUME BIT(VMX_RUN_VMRESUME_SHIFT)
++#define VMX_RUN_SAVE_SPEC_CTRL BIT(VMX_RUN_SAVE_SPEC_CTRL_SHIFT)
+
+ #endif /* __KVM_X86_VMX_RUN_FLAGS_H */
+--- a/arch/x86/kvm/vmx/vmenter.S
++++ b/arch/x86/kvm/vmx/vmenter.S
+@@ -77,7 +77,7 @@ SYM_FUNC_START(__vmx_vcpu_run)
+ mov (%_ASM_SP), %_ASM_AX
+
+ /* Check if vmlaunch or vmresume is needed */
+- testb $VMX_RUN_VMRESUME, %bl
++ bt $VMX_RUN_VMRESUME_SHIFT, %bx
+
+ /* Load guest registers. Don't clobber flags. */
+ mov VCPU_RCX(%_ASM_AX), %_ASM_CX
+@@ -99,8 +99,8 @@ SYM_FUNC_START(__vmx_vcpu_run)
+ /* Load guest RAX. This kills the @regs pointer! */
+ mov VCPU_RAX(%_ASM_AX), %_ASM_AX
+
+- /* Check EFLAGS.ZF from 'testb' above */
+- jz .Lvmlaunch
++ /* Check EFLAGS.CF from the VMX_RUN_VMRESUME bit test above. */
++ jnc .Lvmlaunch
+
+ /*
+ * After a successful VMRESUME/VMLAUNCH, control flow "magically"
--- /dev/null
+From stable+bounces-27533-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:46 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:36 -0700
+Subject: KVM/x86: Export RFDS_NO and RFDS_CLEAR to guests
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Josh Poimboeuf <jpoimboe@kernel.org>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-11-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 2a0180129d726a4b953232175857d442651b55a0 upstream.
+
+Mitigation for RFDS requires RFDS_CLEAR capability which is enumerated
+by MSR_IA32_ARCH_CAPABILITIES bit 27. If the host has it set, export it
+to guests so that they can deploy the mitigation.
+
+RFDS_NO indicates that the system is not vulnerable to RFDS, export it
+to guests so that they don't deploy the mitigation unnecessarily. When
+the host is not affected by X86_BUG_RFDS, but has RFDS_NO=0, synthesize
+RFDS_NO to the guest.
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
+Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kvm/x86.c | 5 ++++-
+ 1 file changed, 4 insertions(+), 1 deletion(-)
+
+--- a/arch/x86/kvm/x86.c
++++ b/arch/x86/kvm/x86.c
+@@ -1498,7 +1498,8 @@ static unsigned int num_msr_based_featur
+ ARCH_CAP_SKIP_VMENTRY_L1DFLUSH | ARCH_CAP_SSB_NO | ARCH_CAP_MDS_NO | \
+ ARCH_CAP_PSCHANGE_MC_NO | ARCH_CAP_TSX_CTRL_MSR | ARCH_CAP_TAA_NO | \
+ ARCH_CAP_SBDR_SSDP_NO | ARCH_CAP_FBSDP_NO | ARCH_CAP_PSDP_NO | \
+- ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | ARCH_CAP_GDS_NO)
++ ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | ARCH_CAP_GDS_NO | \
++ ARCH_CAP_RFDS_NO | ARCH_CAP_RFDS_CLEAR)
+
+ static u64 kvm_get_arch_capabilities(void)
+ {
+@@ -1535,6 +1536,8 @@ static u64 kvm_get_arch_capabilities(voi
+ data |= ARCH_CAP_SSB_NO;
+ if (!boot_cpu_has_bug(X86_BUG_MDS))
+ data |= ARCH_CAP_MDS_NO;
++ if (!boot_cpu_has_bug(X86_BUG_RFDS))
++ data |= ARCH_CAP_RFDS_NO;
+
+ if (!boot_cpu_has(X86_FEATURE_RTM)) {
+ /*
tty-serial-imx-fix-broken-rs485.patch
kvm-arm64-work-out-supported-block-level-at-compile-time.patch
kvm-arm64-limit-stage2_apply_range-batch-size-to-largest-block.patch
+x86-asm-add-_asm_rip-macro-for-x86-64-rip-suffix.patch
+x86-bugs-add-asm-helpers-for-executing-verw.patch
+x86-entry_64-add-verw-just-before-userspace-transition.patch
+x86-entry_32-add-verw-just-before-userspace-transition.patch
+x86-bugs-use-alternative-instead-of-mds_user_clear-static-key.patch
+kvm-vmx-use-bt-jnc-i.e.-eflags.cf-to-select-vmresume-vs.-vmlaunch.patch
+kvm-vmx-move-verw-closer-to-vmentry-for-mds-mitigation.patch
+x86-mmio-disable-kvm-mitigation-when-x86_feature_clear_cpu_buf-is-set.patch
+documentation-hw-vuln-add-documentation-for-rfds.patch
+x86-rfds-mitigate-register-file-data-sampling-rfds.patch
+kvm-x86-export-rfds_no-and-rfds_clear-to-guests.patch
--- /dev/null
+From stable+bounces-27524-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:01 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:10:40 -0700
+Subject: x86/asm: Add _ASM_RIP() macro for x86-64 (%rip) suffix
+To: stable@vger.kernel.org
+Cc: "H. Peter Anvin (Intel)" <hpa@zytor.com>, Borislav Petkov <bp@suse.de>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-1-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
+
+commit f87bc8dc7a7c438c70f97b4e51c76a183313272e upstream.
+
+Add a macro _ASM_RIP() to add a (%rip) suffix on 64 bits only. This is
+useful for immediate memory references where one doesn't want gcc
+to possibly use a register indirection as it may in the case of an "m"
+constraint.
+
+ [ pawan: resolved merged conflict for __ASM_REGPFX ]
+
+Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
+Signed-off-by: Borislav Petkov <bp@suse.de>
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Link: https://lkml.kernel.org/r/20210910195910.2542662-3-hpa@zytor.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/include/asm/asm.h | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+--- a/arch/x86/include/asm/asm.h
++++ b/arch/x86/include/asm/asm.h
+@@ -6,11 +6,13 @@
+ # define __ASM_FORM(x, ...) x,## __VA_ARGS__
+ # define __ASM_FORM_RAW(x, ...) x,## __VA_ARGS__
+ # define __ASM_FORM_COMMA(x, ...) x,## __VA_ARGS__,
++# define __ASM_REGPFX %
+ #else
+ #include <linux/stringify.h>
+ # define __ASM_FORM(x, ...) " " __stringify(x,##__VA_ARGS__) " "
+ # define __ASM_FORM_RAW(x, ...) __stringify(x,##__VA_ARGS__)
+ # define __ASM_FORM_COMMA(x, ...) " " __stringify(x,##__VA_ARGS__) ","
++# define __ASM_REGPFX %%
+ #endif
+
+ #define _ASM_BYTES(x, ...) __ASM_FORM(.byte x,##__VA_ARGS__ ;)
+@@ -49,6 +51,9 @@
+ #define _ASM_SI __ASM_REG(si)
+ #define _ASM_DI __ASM_REG(di)
+
++/* Adds a (%rip) suffix on 64 bits only; for immediate memory references */
++#define _ASM_RIP(x) __ASM_SEL_RAW(x, x (__ASM_REGPFX rip))
++
+ #ifndef __x86_64__
+ /* 32 bit */
+
--- /dev/null
+From stable+bounces-27523-greg=kroah.com@vger.kernel.org Tue Mar 12 22:10:59 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:10:46 -0700
+Subject: x86/bugs: Add asm helpers for executing VERW
+To: stable@vger.kernel.org
+Cc: Alyssa Milburn <alyssa.milburn@intel.com>, Andrew Cooper <andrew.cooper3@citrix.com>, Peter Zijlstra <peterz@infradead.org>, Dave Hansen <dave.hansen@linux.intel.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-2-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit baf8361e54550a48a7087b603313ad013cc13386 upstream.
+
+MDS mitigation requires clearing the CPU buffers before returning to
+user. This needs to be done late in the exit-to-user path. Current
+location of VERW leaves a possibility of kernel data ending up in CPU
+buffers for memory accesses done after VERW such as:
+
+ 1. Kernel data accessed by an NMI between VERW and return-to-user can
+ remain in CPU buffers since NMI returning to kernel does not
+ execute VERW to clear CPU buffers.
+ 2. Alyssa reported that after VERW is executed,
+ CONFIG_GCC_PLUGIN_STACKLEAK=y scrubs the stack used by a system
+ call. Memory accesses during stack scrubbing can move kernel stack
+ contents into CPU buffers.
+ 3. When caller saved registers are restored after a return from
+ function executing VERW, the kernel stack accesses can remain in
+ CPU buffers(since they occur after VERW).
+
+To fix this VERW needs to be moved very late in exit-to-user path.
+
+In preparation for moving VERW to entry/exit asm code, create macros
+that can be used in asm. Also make VERW patching depend on a new feature
+flag X86_FEATURE_CLEAR_CPU_BUF.
+
+ [pawan: - Runtime patch jmp instead of verw in macro CLEAR_CPU_BUFFERS
+ due to lack of relative addressing support for relocations
+ in kernels < v6.5.
+ - Add UNWIND_HINT_EMPTY to avoid warning:
+ arch/x86/entry/entry.o: warning: objtool: mds_verw_sel+0x0: unreachable instruction]
+
+Reported-by: Alyssa Milburn <alyssa.milburn@intel.com>
+Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
+Suggested-by: Peter Zijlstra <peterz@infradead.org>
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-1-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/entry/entry.S | 23 +++++++++++++++++++++++
+ arch/x86/include/asm/cpufeatures.h | 2 +-
+ arch/x86/include/asm/nospec-branch.h | 15 +++++++++++++++
+ 3 files changed, 39 insertions(+), 1 deletion(-)
+
+--- a/arch/x86/entry/entry.S
++++ b/arch/x86/entry/entry.S
+@@ -6,6 +6,9 @@
+ #include <linux/linkage.h>
+ #include <asm/export.h>
+ #include <asm/msr-index.h>
++#include <asm/unwind_hints.h>
++#include <asm/segment.h>
++#include <asm/cache.h>
+
+ .pushsection .noinstr.text, "ax"
+
+@@ -20,3 +23,23 @@ SYM_FUNC_END(entry_ibpb)
+ EXPORT_SYMBOL_GPL(entry_ibpb);
+
+ .popsection
++
++/*
++ * Define the VERW operand that is disguised as entry code so that
++ * it can be referenced with KPTI enabled. This ensure VERW can be
++ * used late in exit-to-user path after page tables are switched.
++ */
++.pushsection .entry.text, "ax"
++
++.align L1_CACHE_BYTES, 0xcc
++SYM_CODE_START_NOALIGN(mds_verw_sel)
++ UNWIND_HINT_EMPTY
++ ANNOTATE_NOENDBR
++ .word __KERNEL_DS
++.align L1_CACHE_BYTES, 0xcc
++SYM_CODE_END(mds_verw_sel);
++/* For KVM */
++EXPORT_SYMBOL_GPL(mds_verw_sel);
++
++.popsection
++
+--- a/arch/x86/include/asm/cpufeatures.h
++++ b/arch/x86/include/asm/cpufeatures.h
+@@ -302,7 +302,7 @@
+ #define X86_FEATURE_UNRET (11*32+15) /* "" AMD BTB untrain return */
+ #define X86_FEATURE_USE_IBPB_FW (11*32+16) /* "" Use IBPB during runtime firmware calls */
+ #define X86_FEATURE_RSB_VMEXIT_LITE (11*32+17) /* "" Fill RSB on VM exit when EIBRS is enabled */
+-
++#define X86_FEATURE_CLEAR_CPU_BUF (11*32+18) /* "" Clear CPU buffers using VERW */
+
+ #define X86_FEATURE_MSR_TSX_CTRL (11*32+20) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
+
+--- a/arch/x86/include/asm/nospec-branch.h
++++ b/arch/x86/include/asm/nospec-branch.h
+@@ -182,6 +182,19 @@
+ #endif
+ .endm
+
++/*
++ * Macro to execute VERW instruction that mitigate transient data sampling
++ * attacks such as MDS. On affected systems a microcode update overloaded VERW
++ * instruction to also clear the CPU buffers. VERW clobbers CFLAGS.ZF.
++ *
++ * Note: Only the memory operand variant of VERW clears the CPU buffers.
++ */
++.macro CLEAR_CPU_BUFFERS
++ ALTERNATIVE "jmp .Lskip_verw_\@", "", X86_FEATURE_CLEAR_CPU_BUF
++ verw _ASM_RIP(mds_verw_sel)
++.Lskip_verw_\@:
++.endm
++
+ #else /* __ASSEMBLY__ */
+
+ #define ANNOTATE_RETPOLINE_SAFE \
+@@ -364,6 +377,8 @@ DECLARE_STATIC_KEY_FALSE(switch_mm_cond_
+
+ DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear);
+
++extern u16 mds_verw_sel;
++
+ #include <asm/segment.h>
+
+ /**
--- /dev/null
+From stable+bounces-27527-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:10 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:02 -0700
+Subject: x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-5-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 6613d82e617dd7eb8b0c40b2fe3acea655b1d611 upstream.
+
+The VERW mitigation at exit-to-user is enabled via a static branch
+mds_user_clear. This static branch is never toggled after boot, and can
+be safely replaced with an ALTERNATIVE() which is convenient to use in
+asm.
+
+Switch to ALTERNATIVE() to use the VERW mitigation late in exit-to-user
+path. Also remove the now redundant VERW in exc_nmi() and
+arch_exit_to_user_mode().
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-4-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ Documentation/x86/mds.rst | 36 +++++++++++++++++++++++++----------
+ arch/x86/include/asm/entry-common.h | 1
+ arch/x86/include/asm/nospec-branch.h | 12 -----------
+ arch/x86/kernel/cpu/bugs.c | 15 +++++---------
+ arch/x86/kernel/nmi.c | 3 --
+ arch/x86/kvm/vmx/vmx.c | 2 -
+ 6 files changed, 33 insertions(+), 36 deletions(-)
+
+--- a/Documentation/x86/mds.rst
++++ b/Documentation/x86/mds.rst
+@@ -95,6 +95,9 @@ The kernel provides a function to invoke
+
+ mds_clear_cpu_buffers()
+
++Also macro CLEAR_CPU_BUFFERS can be used in ASM late in exit-to-user path.
++Other than CFLAGS.ZF, this macro doesn't clobber any registers.
++
+ The mitigation is invoked on kernel/userspace, hypervisor/guest and C-state
+ (idle) transitions.
+
+@@ -138,17 +141,30 @@ Mitigation points
+
+ When transitioning from kernel to user space the CPU buffers are flushed
+ on affected CPUs when the mitigation is not disabled on the kernel
+- command line. The migitation is enabled through the static key
+- mds_user_clear.
++ command line. The mitigation is enabled through the feature flag
++ X86_FEATURE_CLEAR_CPU_BUF.
+
+- The mitigation is invoked in prepare_exit_to_usermode() which covers
+- all but one of the kernel to user space transitions. The exception
+- is when we return from a Non Maskable Interrupt (NMI), which is
+- handled directly in do_nmi().
+-
+- (The reason that NMI is special is that prepare_exit_to_usermode() can
+- enable IRQs. In NMI context, NMIs are blocked, and we don't want to
+- enable IRQs with NMIs blocked.)
++ The mitigation is invoked just before transitioning to userspace after
++ user registers are restored. This is done to minimize the window in
++ which kernel data could be accessed after VERW e.g. via an NMI after
++ VERW.
++
++ **Corner case not handled**
++ Interrupts returning to kernel don't clear CPUs buffers since the
++ exit-to-user path is expected to do that anyways. But, there could be
++ a case when an NMI is generated in kernel after the exit-to-user path
++ has cleared the buffers. This case is not handled and NMI returning to
++ kernel don't clear CPU buffers because:
++
++ 1. It is rare to get an NMI after VERW, but before returning to userspace.
++ 2. For an unprivileged user, there is no known way to make that NMI
++ less rare or target it.
++ 3. It would take a large number of these precisely-timed NMIs to mount
++ an actual attack. There's presumably not enough bandwidth.
++ 4. The NMI in question occurs after a VERW, i.e. when user state is
++ restored and most interesting data is already scrubbed. Whats left
++ is only the data that NMI touches, and that may or may not be of
++ any interest.
+
+
+ 2. C-State transition
+--- a/arch/x86/include/asm/entry-common.h
++++ b/arch/x86/include/asm/entry-common.h
+@@ -91,7 +91,6 @@ static inline void arch_exit_to_user_mod
+
+ static __always_inline void arch_exit_to_user_mode(void)
+ {
+- mds_user_clear_cpu_buffers();
+ amd_clear_divider();
+ }
+ #define arch_exit_to_user_mode arch_exit_to_user_mode
+--- a/arch/x86/include/asm/nospec-branch.h
++++ b/arch/x86/include/asm/nospec-branch.h
+@@ -370,7 +370,6 @@ DECLARE_STATIC_KEY_FALSE(switch_to_cond_
+ DECLARE_STATIC_KEY_FALSE(switch_mm_cond_ibpb);
+ DECLARE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
+
+-DECLARE_STATIC_KEY_FALSE(mds_user_clear);
+ DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
+
+ DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
+@@ -405,17 +404,6 @@ static __always_inline void mds_clear_cp
+ }
+
+ /**
+- * mds_user_clear_cpu_buffers - Mitigation for MDS and TAA vulnerability
+- *
+- * Clear CPU buffers if the corresponding static key is enabled
+- */
+-static __always_inline void mds_user_clear_cpu_buffers(void)
+-{
+- if (static_branch_likely(&mds_user_clear))
+- mds_clear_cpu_buffers();
+-}
+-
+-/**
+ * mds_idle_clear_cpu_buffers - Mitigation for MDS vulnerability
+ *
+ * Clear CPU buffers if the corresponding static key is enabled
+--- a/arch/x86/kernel/cpu/bugs.c
++++ b/arch/x86/kernel/cpu/bugs.c
+@@ -110,9 +110,6 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_cond_i
+ /* Control unconditional IBPB in switch_mm() */
+ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
+
+-/* Control MDS CPU buffer clear before returning to user space */
+-DEFINE_STATIC_KEY_FALSE(mds_user_clear);
+-EXPORT_SYMBOL_GPL(mds_user_clear);
+ /* Control MDS CPU buffer clear before idling (halt, mwait) */
+ DEFINE_STATIC_KEY_FALSE(mds_idle_clear);
+ EXPORT_SYMBOL_GPL(mds_idle_clear);
+@@ -258,7 +255,7 @@ static void __init mds_select_mitigation
+ if (!boot_cpu_has(X86_FEATURE_MD_CLEAR))
+ mds_mitigation = MDS_MITIGATION_VMWERV;
+
+- static_branch_enable(&mds_user_clear);
++ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+
+ if (!boot_cpu_has(X86_BUG_MSBDS_ONLY) &&
+ (mds_nosmt || cpu_mitigations_auto_nosmt()))
+@@ -362,7 +359,7 @@ static void __init taa_select_mitigation
+ * For guests that can't determine whether the correct microcode is
+ * present on host, enable the mitigation for UCODE_NEEDED as well.
+ */
+- static_branch_enable(&mds_user_clear);
++ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+
+ if (taa_nosmt || cpu_mitigations_auto_nosmt())
+ cpu_smt_disable(false);
+@@ -430,7 +427,7 @@ static void __init mmio_select_mitigatio
+ */
+ if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
+ boot_cpu_has(X86_FEATURE_RTM)))
+- static_branch_enable(&mds_user_clear);
++ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+ else
+ static_branch_enable(&mmio_stale_data_clear);
+
+@@ -490,12 +487,12 @@ static void __init md_clear_update_mitig
+ if (cpu_mitigations_off())
+ return;
+
+- if (!static_key_enabled(&mds_user_clear))
++ if (!boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
+ goto out;
+
+ /*
+- * mds_user_clear is now enabled. Update MDS, TAA and MMIO Stale Data
+- * mitigation, if necessary.
++ * X86_FEATURE_CLEAR_CPU_BUF is now enabled. Update MDS, TAA and MMIO
++ * Stale Data mitigation, if necessary.
+ */
+ if (mds_mitigation == MDS_MITIGATION_OFF &&
+ boot_cpu_has_bug(X86_BUG_MDS)) {
+--- a/arch/x86/kernel/nmi.c
++++ b/arch/x86/kernel/nmi.c
+@@ -519,9 +519,6 @@ nmi_restart:
+ write_cr2(this_cpu_read(nmi_cr2));
+ if (this_cpu_dec_return(nmi_state))
+ goto nmi_restart;
+-
+- if (user_mode(regs))
+- mds_user_clear_cpu_buffers();
+ }
+
+ #if defined(CONFIG_X86_64) && IS_ENABLED(CONFIG_KVM_INTEL)
+--- a/arch/x86/kvm/vmx/vmx.c
++++ b/arch/x86/kvm/vmx/vmx.c
+@@ -6750,7 +6750,7 @@ static noinstr void vmx_vcpu_enter_exit(
+ /* L1D Flush includes CPU buffer clear to mitigate MDS */
+ if (static_branch_unlikely(&vmx_l1d_should_flush))
+ vmx_l1d_flush(vcpu);
+- else if (static_branch_unlikely(&mds_user_clear))
++ else if (cpu_feature_enabled(X86_FEATURE_CLEAR_CPU_BUF))
+ mds_clear_cpu_buffers();
+ else if (static_branch_unlikely(&mmio_stale_data_clear) &&
+ kvm_arch_has_assigned_device(vcpu->kvm))
--- /dev/null
+From stable+bounces-27526-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:07 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:10:57 -0700
+Subject: x86/entry_32: Add VERW just before userspace transition
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-4-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit a0e2dab44d22b913b4c228c8b52b2a104434b0b3 upstream.
+
+As done for entry_64, add support for executing VERW late in exit to
+user path for 32-bit mode.
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-3-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/entry/entry_32.S | 3 +++
+ 1 file changed, 3 insertions(+)
+
+--- a/arch/x86/entry/entry_32.S
++++ b/arch/x86/entry/entry_32.S
+@@ -912,6 +912,7 @@ SYM_FUNC_START(entry_SYSENTER_32)
+ BUG_IF_WRONG_CR3 no_user_check=1
+ popfl
+ popl %eax
++ CLEAR_CPU_BUFFERS
+
+ /*
+ * Return back to the vDSO, which will pop ecx and edx.
+@@ -981,6 +982,7 @@ restore_all_switch_stack:
+
+ /* Restore user state */
+ RESTORE_REGS pop=4 # skip orig_eax/error_code
++ CLEAR_CPU_BUFFERS
+ .Lirq_return:
+ /*
+ * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization
+@@ -1173,6 +1175,7 @@ SYM_CODE_START(asm_exc_nmi)
+
+ /* Not on SYSENTER stack. */
+ call exc_nmi
++ CLEAR_CPU_BUFFERS
+ jmp .Lnmi_return
+
+ .Lnmi_from_sysenter_stack:
--- /dev/null
+From stable+bounces-27525-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:02 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:10:51 -0700
+Subject: x86/entry_64: Add VERW just before userspace transition
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-3-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 3c7501722e6b31a6e56edd23cea5e77dbb9ffd1a upstream.
+
+Mitigation for MDS is to use VERW instruction to clear any secrets in
+CPU Buffers. Any memory accesses after VERW execution can still remain
+in CPU buffers. It is safer to execute VERW late in return to user path
+to minimize the window in which kernel data can end up in CPU buffers.
+There are not many kernel secrets to be had after SWITCH_TO_USER_CR3.
+
+Add support for deploying VERW mitigation after user register state is
+restored. This helps minimize the chances of kernel data ending up into
+CPU buffers after executing VERW.
+
+Note that the mitigation at the new location is not yet enabled.
+
+ Corner case not handled
+ =======================
+ Interrupts returning to kernel don't clear CPUs buffers since the
+ exit-to-user path is expected to do that anyways. But, there could be
+ a case when an NMI is generated in kernel after the exit-to-user path
+ has cleared the buffers. This case is not handled and NMI returning to
+ kernel don't clear CPU buffers because:
+
+ 1. It is rare to get an NMI after VERW, but before returning to user.
+ 2. For an unprivileged user, there is no known way to make that NMI
+ less rare or target it.
+ 3. It would take a large number of these precisely-timed NMIs to mount
+ an actual attack. There's presumably not enough bandwidth.
+ 4. The NMI in question occurs after a VERW, i.e. when user state is
+ restored and most interesting data is already scrubbed. Whats left
+ is only the data that NMI touches, and that may or may not be of
+ any interest.
+
+ [ pawan: resolved conflict for hunk swapgs_restore_regs_and_return_to_usermode ]
+
+Suggested-by: Dave Hansen <dave.hansen@intel.com>
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Link: https://lore.kernel.org/all/20240213-delay-verw-v8-2-a6216d83edb7%40linux.intel.com
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/entry/entry_64.S | 11 +++++++++++
+ arch/x86/entry/entry_64_compat.S | 1 +
+ 2 files changed, 12 insertions(+)
+
+--- a/arch/x86/entry/entry_64.S
++++ b/arch/x86/entry/entry_64.S
+@@ -219,6 +219,7 @@ syscall_return_via_sysret:
+ popq %rdi
+ popq %rsp
+ swapgs
++ CLEAR_CPU_BUFFERS
+ sysretq
+ SYM_CODE_END(entry_SYSCALL_64)
+
+@@ -637,6 +638,7 @@ SYM_INNER_LABEL(swapgs_restore_regs_and_
+ /* Restore RDI. */
+ popq %rdi
+ SWAPGS
++ CLEAR_CPU_BUFFERS
+ INTERRUPT_RETURN
+
+
+@@ -743,6 +745,8 @@ native_irq_return_ldt:
+ */
+ popq %rax /* Restore user RAX */
+
++ CLEAR_CPU_BUFFERS
++
+ /*
+ * RSP now points to an ordinary IRET frame, except that the page
+ * is read-only and RSP[31:16] are preloaded with the userspace
+@@ -1466,6 +1470,12 @@ nmi_restore:
+ movq $0, 5*8(%rsp) /* clear "NMI executing" */
+
+ /*
++ * Skip CLEAR_CPU_BUFFERS here, since it only helps in rare cases like
++ * NMI in kernel after user state is restored. For an unprivileged user
++ * these conditions are hard to meet.
++ */
++
++ /*
+ * iretq reads the "iret" frame and exits the NMI stack in a
+ * single instruction. We are returning to kernel mode, so this
+ * cannot result in a fault. Similarly, we don't need to worry
+@@ -1482,6 +1492,7 @@ SYM_CODE_END(asm_exc_nmi)
+ SYM_CODE_START(ignore_sysret)
+ UNWIND_HINT_EMPTY
+ mov $-ENOSYS, %eax
++ CLEAR_CPU_BUFFERS
+ sysretl
+ SYM_CODE_END(ignore_sysret)
+ #endif
+--- a/arch/x86/entry/entry_64_compat.S
++++ b/arch/x86/entry/entry_64_compat.S
+@@ -319,6 +319,7 @@ sysret32_from_system_call:
+ xorl %r9d, %r9d
+ xorl %r10d, %r10d
+ swapgs
++ CLEAR_CPU_BUFFERS
+ sysretl
+ SYM_CODE_END(entry_SYSCALL_compat)
+
--- /dev/null
+From stable+bounces-27530-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:26 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:19 -0700
+Subject: x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-8-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit e95df4ec0c0c9791941f112db699fae794b9862a upstream.
+
+Currently MMIO Stale Data mitigation for CPUs not affected by MDS/TAA is
+to only deploy VERW at VMentry by enabling mmio_stale_data_clear static
+branch. No mitigation is needed for kernel->user transitions. If such
+CPUs are also affected by RFDS, its mitigation may set
+X86_FEATURE_CLEAR_CPU_BUF to deploy VERW at kernel->user and VMentry.
+This could result in duplicate VERW at VMentry.
+
+Fix this by disabling mmio_stale_data_clear static branch when
+X86_FEATURE_CLEAR_CPU_BUF is enabled.
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/kernel/cpu/bugs.c | 14 ++++++++++++--
+ 1 file changed, 12 insertions(+), 2 deletions(-)
+
+--- a/arch/x86/kernel/cpu/bugs.c
++++ b/arch/x86/kernel/cpu/bugs.c
+@@ -428,6 +428,13 @@ static void __init mmio_select_mitigatio
+ if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
+ boot_cpu_has(X86_FEATURE_RTM)))
+ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
++
++ /*
++ * X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
++ * mitigations, disable KVM-only mitigation in that case.
++ */
++ if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
++ static_branch_disable(&mmio_stale_data_clear);
+ else
+ static_branch_enable(&mmio_stale_data_clear);
+
+@@ -504,8 +511,11 @@ static void __init md_clear_update_mitig
+ taa_mitigation = TAA_MITIGATION_VERW;
+ taa_select_mitigation();
+ }
+- if (mmio_mitigation == MMIO_MITIGATION_OFF &&
+- boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
++ /*
++ * MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
++ * gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
++ */
++ if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
+ mmio_mitigation = MMIO_MITIGATION_VERW;
+ mmio_select_mitigation();
+ }
--- /dev/null
+From stable+bounces-27532-greg=kroah.com@vger.kernel.org Tue Mar 12 22:11:38 2024
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Date: Tue, 12 Mar 2024 14:11:30 -0700
+Subject: x86/rfds: Mitigate Register File Data Sampling (RFDS)
+To: stable@vger.kernel.org
+Cc: Dave Hansen <dave.hansen@linux.intel.com>, Thomas Gleixner <tglx@linutronix.de>, Josh Poimboeuf <jpoimboe@kernel.org>
+Message-ID: <20240312-delay-verw-backport-5-15-y-v2-10-e0f71d17ed1b@linux.intel.com>
+Content-Disposition: inline
+
+From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+
+commit 8076fcde016c9c0e0660543e67bff86cb48a7c9c upstream.
+
+RFDS is a CPU vulnerability that may allow userspace to infer kernel
+stale data previously used in floating point registers, vector registers
+and integer registers. RFDS only affects certain Intel Atom processors.
+
+Intel released a microcode update that uses VERW instruction to clear
+the affected CPU buffers. Unlike MDS, none of the affected cores support
+SMT.
+
+Add RFDS bug infrastructure and enable the VERW based mitigation by
+default, that clears the affected buffers just before exiting to
+userspace. Also add sysfs reporting and cmdline parameter
+"reg_file_data_sampling" to control the mitigation.
+
+For details see:
+Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
+
+ [ pawan: - Resolved conflicts in sysfs reporting.
+ - s/ATOM_GRACEMONT/ALDERLAKE_N/ATOM_GRACEMONT is called
+ ALDERLAKE_N in 6.6. ]
+
+Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
+Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
+Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
+Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ Documentation/ABI/testing/sysfs-devices-system-cpu | 1
+ Documentation/admin-guide/kernel-parameters.txt | 21 +++++
+ arch/x86/Kconfig | 11 ++
+ arch/x86/include/asm/cpufeatures.h | 1
+ arch/x86/include/asm/msr-index.h | 8 ++
+ arch/x86/kernel/cpu/bugs.c | 78 ++++++++++++++++++++-
+ arch/x86/kernel/cpu/common.c | 38 +++++++++-
+ drivers/base/cpu.c | 8 ++
+ include/linux/cpu.h | 2
+ 9 files changed, 162 insertions(+), 6 deletions(-)
+
+--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
++++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
+@@ -517,6 +517,7 @@ What: /sys/devices/system/cpu/vulnerabi
+ /sys/devices/system/cpu/vulnerabilities/mds
+ /sys/devices/system/cpu/vulnerabilities/meltdown
+ /sys/devices/system/cpu/vulnerabilities/mmio_stale_data
++ /sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
+ /sys/devices/system/cpu/vulnerabilities/retbleed
+ /sys/devices/system/cpu/vulnerabilities/spec_store_bypass
+ /sys/devices/system/cpu/vulnerabilities/spectre_v1
+--- a/Documentation/admin-guide/kernel-parameters.txt
++++ b/Documentation/admin-guide/kernel-parameters.txt
+@@ -1037,6 +1037,26 @@
+ The filter can be disabled or changed to another
+ driver later using sysfs.
+
++ reg_file_data_sampling=
++ [X86] Controls mitigation for Register File Data
++ Sampling (RFDS) vulnerability. RFDS is a CPU
++ vulnerability which may allow userspace to infer
++ kernel data values previously stored in floating point
++ registers, vector registers, or integer registers.
++ RFDS only affects Intel Atom processors.
++
++ on: Turns ON the mitigation.
++ off: Turns OFF the mitigation.
++
++ This parameter overrides the compile time default set
++ by CONFIG_MITIGATION_RFDS. Mitigation cannot be
++ disabled when other VERW based mitigations (like MDS)
++ are enabled. In order to disable RFDS mitigation all
++ VERW based mitigations need to be disabled.
++
++ For details see:
++ Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
++
+ driver_async_probe= [KNL]
+ List of driver names to be probed asynchronously.
+ Format: <driver_name1>,<driver_name2>...
+@@ -3070,6 +3090,7 @@
+ nopti [X86,PPC]
+ nospectre_v1 [X86,PPC]
+ nospectre_v2 [X86,PPC,S390,ARM64]
++ reg_file_data_sampling=off [X86]
+ retbleed=off [X86]
+ spec_store_bypass_disable=off [X86,PPC]
+ spectre_v2_user=off [X86]
+--- a/arch/x86/Kconfig
++++ b/arch/x86/Kconfig
+@@ -2492,6 +2492,17 @@ config GDS_FORCE_MITIGATION
+
+ If in doubt, say N.
+
++config MITIGATION_RFDS
++ bool "RFDS Mitigation"
++ depends on CPU_SUP_INTEL
++ default y
++ help
++ Enable mitigation for Register File Data Sampling (RFDS) by default.
++ RFDS is a hardware vulnerability which affects Intel Atom CPUs. It
++ allows unprivileged speculative access to stale data previously
++ stored in floating point, vector and integer registers.
++ See also <file:Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst>
++
+ endif
+
+ config ARCH_HAS_ADD_PAGES
+--- a/arch/x86/include/asm/cpufeatures.h
++++ b/arch/x86/include/asm/cpufeatures.h
+@@ -467,4 +467,5 @@
+ /* BUG word 2 */
+ #define X86_BUG_SRSO X86_BUG(1*32 + 0) /* AMD SRSO bug */
+ #define X86_BUG_DIV0 X86_BUG(1*32 + 1) /* AMD DIV0 speculation bug */
++#define X86_BUG_RFDS X86_BUG(1*32 + 2) /* CPU is vulnerable to Register File Data Sampling */
+ #endif /* _ASM_X86_CPUFEATURES_H */
+--- a/arch/x86/include/asm/msr-index.h
++++ b/arch/x86/include/asm/msr-index.h
+@@ -168,6 +168,14 @@
+ * CPU is not vulnerable to Gather
+ * Data Sampling (GDS).
+ */
++#define ARCH_CAP_RFDS_NO BIT(27) /*
++ * Not susceptible to Register
++ * File Data Sampling.
++ */
++#define ARCH_CAP_RFDS_CLEAR BIT(28) /*
++ * VERW clears CPU Register
++ * File.
++ */
+
+ #define MSR_IA32_FLUSH_CMD 0x0000010b
+ #define L1D_FLUSH BIT(0) /*
+--- a/arch/x86/kernel/cpu/bugs.c
++++ b/arch/x86/kernel/cpu/bugs.c
+@@ -487,6 +487,57 @@ static int __init mmio_stale_data_parse_
+ early_param("mmio_stale_data", mmio_stale_data_parse_cmdline);
+
+ #undef pr_fmt
++#define pr_fmt(fmt) "Register File Data Sampling: " fmt
++
++enum rfds_mitigations {
++ RFDS_MITIGATION_OFF,
++ RFDS_MITIGATION_VERW,
++ RFDS_MITIGATION_UCODE_NEEDED,
++};
++
++/* Default mitigation for Register File Data Sampling */
++static enum rfds_mitigations rfds_mitigation __ro_after_init =
++ IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_VERW : RFDS_MITIGATION_OFF;
++
++static const char * const rfds_strings[] = {
++ [RFDS_MITIGATION_OFF] = "Vulnerable",
++ [RFDS_MITIGATION_VERW] = "Mitigation: Clear Register File",
++ [RFDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
++};
++
++static void __init rfds_select_mitigation(void)
++{
++ if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off()) {
++ rfds_mitigation = RFDS_MITIGATION_OFF;
++ return;
++ }
++ if (rfds_mitigation == RFDS_MITIGATION_OFF)
++ return;
++
++ if (x86_read_arch_cap_msr() & ARCH_CAP_RFDS_CLEAR)
++ setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
++ else
++ rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
++}
++
++static __init int rfds_parse_cmdline(char *str)
++{
++ if (!str)
++ return -EINVAL;
++
++ if (!boot_cpu_has_bug(X86_BUG_RFDS))
++ return 0;
++
++ if (!strcmp(str, "off"))
++ rfds_mitigation = RFDS_MITIGATION_OFF;
++ else if (!strcmp(str, "on"))
++ rfds_mitigation = RFDS_MITIGATION_VERW;
++
++ return 0;
++}
++early_param("reg_file_data_sampling", rfds_parse_cmdline);
++
++#undef pr_fmt
+ #define pr_fmt(fmt) "" fmt
+
+ static void __init md_clear_update_mitigation(void)
+@@ -519,6 +570,11 @@ static void __init md_clear_update_mitig
+ mmio_mitigation = MMIO_MITIGATION_VERW;
+ mmio_select_mitigation();
+ }
++ if (rfds_mitigation == RFDS_MITIGATION_OFF &&
++ boot_cpu_has_bug(X86_BUG_RFDS)) {
++ rfds_mitigation = RFDS_MITIGATION_VERW;
++ rfds_select_mitigation();
++ }
+ out:
+ if (boot_cpu_has_bug(X86_BUG_MDS))
+ pr_info("MDS: %s\n", mds_strings[mds_mitigation]);
+@@ -528,6 +584,8 @@ out:
+ pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]);
+ else if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
+ pr_info("MMIO Stale Data: Unknown: No mitigations\n");
++ if (boot_cpu_has_bug(X86_BUG_RFDS))
++ pr_info("Register File Data Sampling: %s\n", rfds_strings[rfds_mitigation]);
+ }
+
+ static void __init md_clear_select_mitigation(void)
+@@ -535,11 +593,12 @@ static void __init md_clear_select_mitig
+ mds_select_mitigation();
+ taa_select_mitigation();
+ mmio_select_mitigation();
++ rfds_select_mitigation();
+
+ /*
+- * As MDS, TAA and MMIO Stale Data mitigations are inter-related, update
+- * and print their mitigation after MDS, TAA and MMIO Stale Data
+- * mitigation selection is done.
++ * As these mitigations are inter-related and rely on VERW instruction
++ * to clear the microarchitural buffers, update and print their status
++ * after mitigation selection is done for each of these vulnerabilities.
+ */
+ md_clear_update_mitigation();
+ }
+@@ -2600,6 +2659,11 @@ static ssize_t mmio_stale_data_show_stat
+ sched_smt_active() ? "vulnerable" : "disabled");
+ }
+
++static ssize_t rfds_show_state(char *buf)
++{
++ return sysfs_emit(buf, "%s\n", rfds_strings[rfds_mitigation]);
++}
++
+ static char *stibp_state(void)
+ {
+ if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
+@@ -2760,6 +2824,9 @@ static ssize_t cpu_show_common(struct de
+ case X86_BUG_SRSO:
+ return srso_show_state(buf);
+
++ case X86_BUG_RFDS:
++ return rfds_show_state(buf);
++
+ default:
+ break;
+ }
+@@ -2834,4 +2901,9 @@ ssize_t cpu_show_spec_rstack_overflow(st
+ {
+ return cpu_show_common(dev, attr, buf, X86_BUG_SRSO);
+ }
++
++ssize_t cpu_show_reg_file_data_sampling(struct device *dev, struct device_attribute *attr, char *buf)
++{
++ return cpu_show_common(dev, attr, buf, X86_BUG_RFDS);
++}
+ #endif
+--- a/arch/x86/kernel/cpu/common.c
++++ b/arch/x86/kernel/cpu/common.c
+@@ -1138,6 +1138,8 @@ static const __initconst struct x86_cpu_
+ #define SRSO BIT(5)
+ /* CPU is affected by GDS */
+ #define GDS BIT(6)
++/* CPU is affected by Register File Data Sampling */
++#define RFDS BIT(7)
+
+ static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = {
+ VULNBL_INTEL_STEPPINGS(IVYBRIDGE, X86_STEPPING_ANY, SRBDS),
+@@ -1165,9 +1167,18 @@ static const struct x86_cpu_id cpu_vuln_
+ VULNBL_INTEL_STEPPINGS(TIGERLAKE, X86_STEPPING_ANY, GDS),
+ VULNBL_INTEL_STEPPINGS(LAKEFIELD, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RETBLEED),
+ VULNBL_INTEL_STEPPINGS(ROCKETLAKE, X86_STEPPING_ANY, MMIO | RETBLEED | GDS),
+- VULNBL_INTEL_STEPPINGS(ATOM_TREMONT, X86_STEPPING_ANY, MMIO | MMIO_SBDS),
+- VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D, X86_STEPPING_ANY, MMIO),
+- VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L, X86_STEPPING_ANY, MMIO | MMIO_SBDS),
++ VULNBL_INTEL_STEPPINGS(ALDERLAKE, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(ALDERLAKE_L, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(RAPTORLAKE, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(RAPTORLAKE_P, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(RAPTORLAKE_S, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(ALDERLAKE_N, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_TREMONT, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D, X86_STEPPING_ANY, MMIO | RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT_D, X86_STEPPING_ANY, RFDS),
++ VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT_PLUS, X86_STEPPING_ANY, RFDS),
+
+ VULNBL_AMD(0x15, RETBLEED),
+ VULNBL_AMD(0x16, RETBLEED),
+@@ -1201,6 +1212,24 @@ static bool arch_cap_mmio_immune(u64 ia3
+ ia32_cap & ARCH_CAP_SBDR_SSDP_NO);
+ }
+
++static bool __init vulnerable_to_rfds(u64 ia32_cap)
++{
++ /* The "immunity" bit trumps everything else: */
++ if (ia32_cap & ARCH_CAP_RFDS_NO)
++ return false;
++
++ /*
++ * VMMs set ARCH_CAP_RFDS_CLEAR for processors not in the blacklist to
++ * indicate that mitigation is needed because guest is running on a
++ * vulnerable hardware or may migrate to such hardware:
++ */
++ if (ia32_cap & ARCH_CAP_RFDS_CLEAR)
++ return true;
++
++ /* Only consult the blacklist when there is no enumeration: */
++ return cpu_matches(cpu_vuln_blacklist, RFDS);
++}
++
+ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
+ {
+ u64 ia32_cap = x86_read_arch_cap_msr();
+@@ -1312,6 +1341,9 @@ static void __init cpu_set_bug_bits(stru
+ setup_force_cpu_bug(X86_BUG_SRSO);
+ }
+
++ if (vulnerable_to_rfds(ia32_cap))
++ setup_force_cpu_bug(X86_BUG_RFDS);
++
+ if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
+ return;
+
+--- a/drivers/base/cpu.c
++++ b/drivers/base/cpu.c
+@@ -589,6 +589,12 @@ ssize_t __weak cpu_show_spec_rstack_over
+ return sysfs_emit(buf, "Not affected\n");
+ }
+
++ssize_t __weak cpu_show_reg_file_data_sampling(struct device *dev,
++ struct device_attribute *attr, char *buf)
++{
++ return sysfs_emit(buf, "Not affected\n");
++}
++
+ static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
+ static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
+ static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
+@@ -602,6 +608,7 @@ static DEVICE_ATTR(mmio_stale_data, 0444
+ static DEVICE_ATTR(retbleed, 0444, cpu_show_retbleed, NULL);
+ static DEVICE_ATTR(gather_data_sampling, 0444, cpu_show_gds, NULL);
+ static DEVICE_ATTR(spec_rstack_overflow, 0444, cpu_show_spec_rstack_overflow, NULL);
++static DEVICE_ATTR(reg_file_data_sampling, 0444, cpu_show_reg_file_data_sampling, NULL);
+
+ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
+ &dev_attr_meltdown.attr,
+@@ -617,6 +624,7 @@ static struct attribute *cpu_root_vulner
+ &dev_attr_retbleed.attr,
+ &dev_attr_gather_data_sampling.attr,
+ &dev_attr_spec_rstack_overflow.attr,
++ &dev_attr_reg_file_data_sampling.attr,
+ NULL
+ };
+
+--- a/include/linux/cpu.h
++++ b/include/linux/cpu.h
+@@ -74,6 +74,8 @@ extern ssize_t cpu_show_spec_rstack_over
+ struct device_attribute *attr, char *buf);
+ extern ssize_t cpu_show_gds(struct device *dev,
+ struct device_attribute *attr, char *buf);
++extern ssize_t cpu_show_reg_file_data_sampling(struct device *dev,
++ struct device_attribute *attr, char *buf);
+
+ extern __printf(4, 5)
+ struct device *cpu_device_create(struct device *parent, void *drvdata,
projects / thirdparty / kernel / stable-queue.git / commitdiff
