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x86/sev: Prevent GUEST_TSC_FREQ MSR interception for Secure TSC enabled guests

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The hypervisor should not be intercepting GUEST_TSC_FREQ MSR(0xcOO10134)
when Secure TSC is enabled. A #VC exception will be generated otherwise. If
this should occur and Secure TSC is enabled, terminate guest execution.

Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20250106124633.1418972-8-nikunj@amd.com
This commit is contained in:
Nikunj A Dadhania 2025-01-06 18:16:27 +05:30 • committed by Borislav Petkov (AMD)
parent 0f0502b886
commit 38cc6495cd
2 changed files with 10 additions and 1 deletions
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10
arch/x86/coco/sev/core.c
View file

@ -1436,12 +1436,19 @@ static enum es_result __vc_handle_msr_caa(struct pt_regs *regs, bool write)
/*
* TSC related accesses should not exit to the hypervisor when a guest is
* executing with Secure TSC enabled, so special handling is required for
* accesses of MSR_IA32_TSC.
* accesses of MSR_IA32_TSC and MSR_AMD64_GUEST_TSC_FREQ.
*/
static enum es_result __vc_handle_secure_tsc_msrs(struct pt_regs *regs, bool write)
{
u64 tsc;
/*
* GUEST_TSC_FREQ should not be intercepted when Secure TSC is enabled.
* Terminate the SNP guest when the interception is enabled.
*/
if (regs->cx == MSR_AMD64_GUEST_TSC_FREQ)
return ES_VMM_ERROR;
/*
* Writes: Writing to MSR_IA32_TSC can cause subsequent reads of the TSC
* to return undefined values, so ignore all writes.
@ -1474,6 +1481,7 @@ static enum es_result vc_handle_msr(struct ghcb *ghcb, struct es_em_ctxt *ctxt)
case MSR_SVSM_CAA:
return __vc_handle_msr_caa(regs, write);
case MSR_IA32_TSC:
case MSR_AMD64_GUEST_TSC_FREQ:
if (sev_status & MSR_AMD64_SNP_SECURE_TSC)
return __vc_handle_secure_tsc_msrs(regs, write);
else

1
arch/x86/include/asm/msr-index.h
View file

@ -608,6 +608,7 @@
#define MSR_AMD_PERF_CTL 0xc0010062
#define MSR_AMD_PERF_STATUS 0xc0010063
#define MSR_AMD_PSTATE_DEF_BASE 0xc0010064
#define MSR_AMD64_GUEST_TSC_FREQ 0xc0010134
#define MSR_AMD64_OSVW_ID_LENGTH 0xc0010140
#define MSR_AMD64_OSVW_STATUS 0xc0010141
#define MSR_AMD_PPIN_CTL 0xc00102f0