Re: [PATCH v15 12/13] x86/kvmclock: Abort SecureTSC enabled guest when kvmclock is selected

Tom Lendacky
2024-12-16T16:37:00Z

On 12/3/24 03:00, Nikunj A Dadhania wrote:
> SecureTSC enabled guests should use TSC as the only clock source, terminate
> the guest with appropriate code when clock source switches to hypervisor
> controlled kvmclock.
>
> Signed-off-by: Nikunj A Dadhania <nikunj@amd.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
> arch/x86/include/asm/sev-common.h | 1 +
> arch/x86/include/asm/sev.h | 2 ++
> arch/x86/coco/sev/shared.c | 3 +--
> arch/x86/kernel/kvmclock.c | 9 +++++++++
> 4 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 6ef92432a5ce..ad0743800b0e 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -207,6 +207,7 @@ struct snp_psc_desc {
> #define GHCB_TERM_SVSM_VMPL0 8 /* SVSM is present but has set VMPL to 0 */
> #define GHCB_TERM_SVSM_CAA 9 /* SVSM is present but CAA is not page aligned */
> #define GHCB_TERM_SECURE_TSC 10 /* Secure TSC initialization failed */
> +#define GHCB_TERM_SECURE_TSC_KVMCLOCK 11 /* KVM clock selected instead of Secure TSC */
>
> #define GHCB_RESP_CODE(v) ((v) & GHCB_MSR_INFO_MASK)
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index c4dca06b3b01..12b167fd6475 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -494,6 +494,7 @@ int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_guest_req *req
>
> void __init snp_secure_tsc_prepare(void);
> void __init snp_secure_tsc_init(void);
> +void __noreturn sev_es_terminate(unsigned int set, unsigned int reason);
>
> #else /* !CONFIG_AMD_MEM_ENCRYPT */
>
> @@ -538,6 +539,7 @@ static inline int snp_send_guest_request(struct snp_msg_desc *mdesc, struct snp_
> struct snp_guest_request_ioctl *rio) { return -ENODEV; }
> static inline void __init snp_secure_tsc_prepare(void) { }
> static inline void __init snp_secure_tsc_init(void) { }
> +static inline void sev_es_terminate(unsigned int set, unsigned int reason) { }
>
> #endif /* CONFIG_AMD_MEM_ENCRYPT */
>
> diff --git a/arch/x86/coco/sev/shared.c b/arch/x86/coco/sev/shared.c
> index 879ab48b705c..840149556241 100644
> --- a/arch/x86/coco/sev/shared.c
> +++ b/arch/x86/coco/sev/shared.c
> @@ -117,8 +117,7 @@ static bool __init sev_es_check_cpu_features(void)
> return true;
> }
>
> -static void __head __noreturn
> -sev_es_terminate(unsigned int set, unsigned int reason)
> +void __head __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
> {
> u64 val = GHCB_MSR_TERM_REQ;
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index 5b2c15214a6b..39dda04b5ba0 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -21,6 +21,7 @@
> #include <asm/hypervisor.h>
> #include <asm/x86_init.h>
> #include <asm/kvmclock.h>
> +#include <asm/sev.h>
>
> static int kvmclock __initdata = 1;
> static int kvmclock_vsyscall __initdata = 1;
> @@ -150,6 +151,14 @@ bool kvm_check_and_clear_guest_paused(void)
>
> static int kvm_cs_enable(struct clocksource *cs)
> {
> + /*
> + * For a guest with SecureTSC enabled, the TSC should be the only clock
> + * source. Abort the guest when kvmclock is selected as the clock
> + * source.
> + */
> + if (WARN_ON(cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)))
> + sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECURE_TSC_KVMCLOCK);
> +
> vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
> return 0;
> }