6.12-stable patches

added patches:
	series
	x86-bugs-make-safe-ret-robust-against-interrupt-injection.patch

diff --git a/queue-6.12/series b/queue-6.12/series
new file mode 100644 (file)
index 0000000..4a6de0f
--- /dev/null
+++ b/queue-6.12/series
@@ -0,0 +1 @@
+x86-bugs-make-safe-ret-robust-against-interrupt-injection.patch

diff --git a/queue-6.12/x86-bugs-make-safe-ret-robust-against-interrupt-injection.patch b/queue-6.12/x86-bugs-make-safe-ret-robust-against-interrupt-injection.patch
new file mode 100644 (file)
index 0000000..df912e4
--- /dev/null
+++ b/queue-6.12/x86-bugs-make-safe-ret-robust-against-interrupt-injection.patch
@@ -0,0 +1,228 @@
+From e7c56e790f05c00a3c548a4233c47bb1083a313a Mon Sep 17 00:00:00 2001
+From: "Borislav Petkov (AMD)" <bp@alien8.de>
+Date: Tue, 2 Jun 2026 21:26:44 -0700
+Subject: x86/bugs: Make Safe-RET robust against interrupt injection
+
+From: "Borislav Petkov (AMD)" <bp@alien8.de>
+
+commit 7e7f81cf6f5ca3311e526308f55d7c54d3ba71f9 upstream.
+
+An attacker injecting interrupts while the Safe-RET mitigation executes
+on machines affected by SRSO can neutralize the safe return sequence,
+potentially leading to data leakage through speculative execution.
+
+Fixup register state as if the Safe-RET sequence executed successfully
+by "emulating" it, in a manner of speaking, and avoid executing a RET
+instruction after returning from the interrupt.
+
+Co-developed-by: David Kaplan <David.Kaplan@amd.com>
+Signed-off-by: David Kaplan <David.Kaplan@amd.com>
+Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ arch/x86/entry/entry_64.S            |    8 ++++
+ arch/x86/include/asm/nospec-branch.h |   59 +++++++++++++++++++++++++++++++++++
+ arch/x86/kernel/cpu/bugs.c           |   39 +++++++++++++++++++++++
+ arch/x86/lib/retpoline.S             |   20 +++++++++++
+ 4 files changed, 125 insertions(+), 1 deletion(-)
+
+--- a/arch/x86/entry/entry_64.S
++++ b/arch/x86/entry/entry_64.S
+@@ -936,6 +936,8 @@ SYM_CODE_START(paranoid_entry)
+       IBRS_ENTER save_reg=%r15
+       UNTRAIN_RET_FROM_CALL
+ 
++      HANDLE_INTR_SAFERET 8(%rsp)
++
+       RET
+ SYM_CODE_END(paranoid_entry)
+ 
+@@ -1038,6 +1040,11 @@ SYM_CODE_START(error_entry)
+       movl    %ecx, %eax                      /* zero extend */
+       cmpq    %rax, RIP+8(%rsp)
+       je      .Lbstep_iret
++
++      VALIDATE_UNRET_END
++
++      HANDLE_INTR_SAFERET 8(%rsp)
++
+       cmpq    $.Lgs_change, RIP+8(%rsp)
+       jne     .Lerror_entry_done_lfence
+ 
+@@ -1056,7 +1063,6 @@ SYM_CODE_START(error_entry)
+       FENCE_SWAPGS_KERNEL_ENTRY
+       CALL_DEPTH_ACCOUNT
+       leaq    8(%rsp), %rax                   /* return pt_regs pointer */
+-      VALIDATE_UNRET_END
+       RET
+ 
+ .Lbstep_iret:
+--- a/arch/x86/include/asm/nospec-branch.h
++++ b/arch/x86/include/asm/nospec-branch.h
+@@ -177,6 +177,53 @@
+       add     $(BITS_PER_LONG/8), %_ASM_SP;           \
+       lfence;
+ 
++/*
++ * Helper for detecting if an interrupt occurred at an unsafe location within
++ * Safe-RET.  If Safe-RET is interrupted after the CALL or LEA the RSB may get
++ * poisoned by the interrupt handler.
++ *
++ * The Safe-RET sequence is:
++ *
++ * CALL
++ * LEA 8(%RSP), %RSP
++ * RET
++ *
++ * The two CMPs below check whether RIP points to after the CALL or after the
++ * LEA.
++ *
++ * The LFENCE below is to address this particular speculation case:
++ *
++ * 1. Userspace runs and poisons the BTB around the safe-RET routine
++ *
++ * 2. Userspace triggers some kind of exception
++ *
++ * 3. Kernel executes error_entry() and mis-speculates the branch into thinking
++ *    it actually came from kernel space
++ *
++ * 4. The kernel then further mis-speculates that the exception occurred due
++ *    to an interrupted safe-RET
++ *
++ * 5. The handle_interrupted_saferet() routine speculatively executes and
++ *    speculatively does a safe-RET. But this is unsafe since it was never
++ *    untrained.
++ *
++ * The LFENCE fixes this by ensuring step 5 is never reached speculatively.
++ * Note that this LFENCE only occurs if safe-RET was actually interrupted (so
++ * it's outside of the normal path).
++ *
++ * (The 128 below is RIP offset, used as a naked number here for ease of
++ * backporting).
++ */
++#define __HANDLE_INTR_SAFERET(name, pt_regs)          \
++      cmpq    $(name), 128+pt_regs;                   \
++      jb      1f;                                     \
++      cmpq    $(name)+5, 128+pt_regs;                 \
++      ja      1f;                                     \
++      lfence;                                         \
++      leaq    pt_regs, %rdi;                          \
++      call    handle_interrupted_saferet;             \
++      1:
++
+ #ifdef __ASSEMBLY__
+ 
+ /*
+@@ -306,6 +353,14 @@
+ #define UNTRAIN_RET_FROM_CALL \
+       __UNTRAIN_RET X86_FEATURE_ENTRY_IBPB, __stringify(RESET_CALL_DEPTH_FROM_CALL)
+ 
++.macro HANDLE_INTR_SAFERET pt_regs
++#ifdef CONFIG_MITIGATION_SRSO
++      ALTERNATIVE_2 "", \
++      __stringify(__HANDLE_INTR_SAFERET(srso_safe_ret, \pt_regs)), X86_FEATURE_SRSO, \
++      __stringify(__HANDLE_INTR_SAFERET(srso_alias_safe_ret, \pt_regs)), X86_FEATURE_SRSO_ALIAS
++
++#endif
++.endm
+ 
+ .macro CALL_DEPTH_ACCOUNT
+ #ifdef CONFIG_MITIGATION_CALL_DEPTH_TRACKING
+@@ -639,6 +694,10 @@ static __always_inline void x86_idle_cle
+               x86_clear_cpu_buffers();
+ }
+ 
++void srso_safe_ret(void);
++void srso_alias_safe_ret(void);
++void handle_interrupted_saferet(struct pt_regs *regs);
++
+ #endif /* __ASSEMBLY__ */
+ 
+ #endif /* _ASM_X86_NOSPEC_BRANCH_H_ */
+--- a/arch/x86/kernel/cpu/bugs.c
++++ b/arch/x86/kernel/cpu/bugs.c
+@@ -3523,3 +3523,42 @@ void __warn_thunk(void)
+ {
+       WARN_ONCE(1, "Unpatched return thunk in use. This should not happen!\n");
+ }
++
++#ifdef CONFIG_MITIGATION_SRSO
++/*
++ * Called during exception/interrupt entry if interrupted during the
++ * safe-RET sequence.  The safe-RET sequence consists of 3 instructions:
++ *
++ *    CALL
++ *    LEA 8(%RSP), %RSP
++ *    RET
++ *
++ * An interrupt after the CALL or after the LEA could potentially lead
++ * to branch predictor poisoning and results in the sequence not being
++ * able to be safely resumed.
++ *
++ * Therefore, modify the regs state as if the remaining part of the
++ * safe-RET sequence executed so the interrupt returns back to the
++ * desired return target, instead of the to the safe-RET sequence.
++ */
++void noinstr handle_interrupted_saferet(struct pt_regs *regs)
++{
++      unsigned long rip = regs->ip;
++
++      if (rip == (unsigned long) srso_safe_ret ||
++          rip == (unsigned long) srso_alias_safe_ret) {
++          /* Modify stack pointer as if LEA executed: */
++          regs->sp += 8;
++      }
++
++      /*
++       * Adjust registers as if RET executed:
++       *
++       * 1. Read the return address off the stack and into rIP:
++       */
++      regs->ip = *(unsigned long *)(regs->sp);
++
++      /* 2. Pop rIP off the stack: */
++      regs->sp += 8;
++}
++#endif /* CONFIG_MITIGATION_SRSO */
+--- a/arch/x86/lib/retpoline.S
++++ b/arch/x86/lib/retpoline.S
+@@ -168,10 +168,24 @@ __EXPORT_THUNK(srso_alias_untrain_ret)
+ 
+       .pushsection .text..__x86.rethunk_safe
+ SYM_CODE_START_NOALIGN(srso_alias_safe_ret)
++
++      /*
++       * Tell objtool that those are not function pointers referenced by
++       * __HANDLE_INTR_SAFERET(). Below too.
++       */
++      ANNOTATE_NOENDBR
++
++      /*
++       * Safe-RET sequence. If you need to change it, adjust
++       * handle_interrupted_saferet() too.
++       */
+       lea 8(%_ASM_SP), %_ASM_SP
+       UNWIND_HINT_FUNC
++
++      ANNOTATE_NOENDBR
+       ANNOTATE_UNRET_SAFE
+       ret
++      /* End of Safe-RET sequence */
+       int3
+ SYM_FUNC_END(srso_alias_safe_ret)
+ 
+@@ -206,8 +220,14 @@ SYM_CODE_START_LOCAL_NOALIGN(srso_untrai
+  * the stack.
+  */
+ SYM_INNER_LABEL(srso_safe_ret, SYM_L_GLOBAL)
++      /*
++       * Safe-RET sequence. If you need to change it, adjust
++       * handle_interrupted_saferet() too.
++       */
+       lea 8(%_ASM_SP), %_ASM_SP
+       ret
++      /* End of Safe-RET sequence */
++
+       int3
+       int3
+       /* end of movabs */