KVM: Add GDS_NO support to KVM

commit 81ac7e5d741742d650b4ed6186c4826c1a0631a7 upstream

Gather Data Sampling (GDS) is a transient execution attack using
gather instructions from the AVX2 and AVX512 extensions. This attack
allows malicious code to infer data that was previously stored in
vector registers. Systems that are not vulnerable to GDS will set the
GDS_NO bit of the IA32_ARCH_CAPABILITIES MSR. This is useful for VM
guests that may think they are on vulnerable systems that are, in
fact, not affected. Guests that are running on affected hosts where
the mitigation is enabled are protected as if they were running
on an unaffected system.

On all hosts that are not affected or that are mitigated, set the
GDS_NO bit.

Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index f9a1293e99205f23db470e1bc257b3b8cd0989f0..322d1a421d8c52ae5113aa0f9b8b56ec98cbbaf9 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -673,6 +673,13 @@ static const char * const gds_strings[] = {
        [GDS_MITIGATION_HYPERVISOR]     = "Unknown: Dependent on hypervisor status",
 };
 
+bool gds_ucode_mitigated(void)
+{
+       return (gds_mitigation == GDS_MITIGATION_FULL ||
+               gds_mitigation == GDS_MITIGATION_FULL_LOCKED);
+}
+EXPORT_SYMBOL_GPL(gds_ucode_mitigated);
+
 void update_gds_msr(void)
 {
        u64 mcu_ctrl_after;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 285ba12be8ce33b3e7e2fc1c5e036a25f2fed2e9..2686c4dcdb1a0b7e188bde8f930250a1fd854fdc 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -303,6 +303,8 @@ static struct kmem_cache *x86_fpu_cache;
 
 static struct kmem_cache *x86_emulator_cache;
 
+extern bool gds_ucode_mitigated(void);
+
 /*
  * When called, it means the previous get/set msr reached an invalid msr.
  * Return true if we want to ignore/silent this failed msr access.
@@ -1498,7 +1500,7 @@ static unsigned int num_msr_based_features;
         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_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | ARCH_CAP_GDS_NO)
 
 static u64 kvm_get_arch_capabilities(void)
 {
@@ -1555,6 +1557,9 @@ static u64 kvm_get_arch_capabilities(void)
                 */
        }
 
+       if (!boot_cpu_has_bug(X86_BUG_GDS) || gds_ucode_mitigated())
+               data |= ARCH_CAP_GDS_NO;
+
        return data;
 }