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x86/bugs: Add SRSO_USER_KERNEL_NO support

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commit 877818802c 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: 7c62c442b6 ("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>
This commit is contained in:
Borislav Petkov (AMD) 2024-11-11 17:22:08 +01:00 committed by Greg Kroah-Hartman
parent 0a3ac13d86
commit f9c6aec2a6
2 changed files with 5 additions and 0 deletions
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1
arch/x86/include/asm/cpufeatures.h
View File

@ -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

4
arch/x86/kernel/cpu/bugs.c
View File

@ -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) {