x86/bugs: Add SRSO_USER_KERNEL_NO support
commit 877818802c3e970f67ccb53012facc78bef5f97a upstream.
If the machine has:
CPUID Fn8000_0021_EAX[30] (SRSO_USER_KERNEL_NO) -- If this bit is 1,
it indicates the CPU is not subject to the SRSO vulnerability across
user/kernel boundaries.
have it fall back to IBPB on VMEXIT only, in the case it is going to run
VMs:
Speculative Return Stack Overflow: Mitigation: IBPB on VMEXIT only
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Link: https://lore.kernel.org/r/20241202120416.6054-2-bp@kernel.org
[ Harshit: Conflicts resolved as this commit: 7c62c442b6eb ("x86/vmscape:
Enumerate VMSCAPE bug") has been applied already to 6.12.y ]
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 90f1f2f..3fc47f2 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -464,6 +464,7 @@
#define X86_FEATURE_SBPB (20*32+27) /* Selective Branch Prediction Barrier */
#define X86_FEATURE_IBPB_BRTYPE (20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */
#define X86_FEATURE_SRSO_NO (20*32+29) /* CPU is not affected by SRSO */
+#define X86_FEATURE_SRSO_USER_KERNEL_NO (20*32+30) /* CPU is not affected by SRSO across user/kernel boundaries */
/*
* Extended auxiliary flags: Linux defined - for features scattered in various
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 06bbc29..c3ea29e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2810,6 +2810,9 @@ static void __init srso_select_mitigation(void)
break;
case SRSO_CMD_SAFE_RET:
+ if (boot_cpu_has(X86_FEATURE_SRSO_USER_KERNEL_NO))
+ goto ibpb_on_vmexit;
+
if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
/*
* Enable the return thunk for generated code
@@ -2861,6 +2864,7 @@ static void __init srso_select_mitigation(void)
}
break;
+ibpb_on_vmexit:
case SRSO_CMD_IBPB_ON_VMEXIT:
if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) {
if (has_microcode) {
