linux-kernel - Re: [PATCH v13 12/13] x86/kvmclock: Abort SecureTSC enabled guest when kvmclock is selected

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Message-ID: <4e43f173-6a89-c1ee-5f1c-2f7e23ebcbad@amd.com>
Date: Mon, 21 Oct 2024 10:00:00 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Nikunj A Dadhania <nikunj@....com>, linux-kernel@...r.kernel.org,
 bp@...en8.de, x86@...nel.org, kvm@...r.kernel.org
Cc: mingo@...hat.com, tglx@...utronix.de, dave.hansen@...ux.intel.com,
 pgonda@...gle.com, seanjc@...gle.com, pbonzini@...hat.com
Subject: Re: [PATCH v13 12/13] x86/kvmclock: Abort SecureTSC enabled guest
 when kvmclock is selected

On 10/21/24 00:51, 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@....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 34f7b9fc363b..783dc57f73c3 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -537,6 +537,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
>  
>  void __init snp_secure_tsc_prepare(void);
>  void __init securetsc_init(void);
> +void __noreturn sev_es_terminate(unsigned int set, unsigned int reason);
>  
>  #else	/* !CONFIG_AMD_MEM_ENCRYPT */
>  
> @@ -586,6 +587,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
>  
>  static inline void __init snp_secure_tsc_prepare(void) { }
>  static inline void __init securetsc_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 c2a9e2ada659..d202790e1385 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..b135044f3c7b 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 (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))

if (WARN_ON(cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)))

so that the guest sees something as well?

Thanks,
Tom

> +		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECURE_TSC_KVMCLOCK);
> +
>  	vclocks_set_used(VDSO_CLOCKMODE_PVCLOCK);
>  	return 0;
>  }