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Date: Fri, 8 Mar 2024 16:33:47 -0800
From: Dionna Amalie Glaze <dionnaglaze@...gle.com>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Dan Williams <dan.j.williams@...el.com>, Michael Roth <michael.roth@....com>,
Ashish Kalra <ashish.kalra@....com>
Subject: Re: [PATCH v2 03/14] x86/sev: Check for the presence of an SVSM in
the SNP Secrets page
On Fri, Mar 8, 2024 at 10:36 AM Tom Lendacky <thomas.lendacky@....com> wrote:
>
> During early boot phases, check for the presence of an SVSM when running
> as an SEV-SNP guest.
>
> An SVSM is present if the 64-bit value at offset 0x148 into the secrets
> page is non-zero. If an SVSM is present, save the SVSM Calling Area
> address (CAA), located at offset 0x150 into the secrets page, and set
> the VMPL level of the guest, which should be non-zero, to indicate the
> presence of an SVSM.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
> arch/x86/boot/compressed/sev.c | 35 ++++++++---------
> arch/x86/include/asm/sev-common.h | 4 ++
> arch/x86/include/asm/sev.h | 25 +++++++++++-
> arch/x86/kernel/sev-shared.c | 64 +++++++++++++++++++++++++++++++
> arch/x86/kernel/sev.c | 16 ++++++++
> 5 files changed, 125 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index bd7222aad540..f54c0ceae1cb 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -12,6 +12,7 @@
> */
> #include "misc.h"
>
> +#include <linux/mm.h>
> #include <asm/bootparam.h>
> #include <asm/pgtable_types.h>
> #include <asm/sev.h>
> @@ -29,6 +30,15 @@
> static struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
> struct ghcb *boot_ghcb;
>
> +/*
> + * SVSM related information:
> + * When running under an SVSM, the VMPL that Linux is executing at must be
> + * non-zero. The VMPL is therefore used to indicate the presence of an SVSM.
> + */
> +static u8 vmpl __section(".data");
> +static u64 boot_svsm_caa_pa __section(".data");
> +static struct svsm_ca *boot_svsm_caa __section(".data");
> +
> /*
> * Copy a version of this function here - insn-eval.c can't be used in
> * pre-decompression code.
> @@ -335,24 +345,6 @@ void do_boot_stage2_vc(struct pt_regs *regs, unsigned long exit_code)
> sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
> }
>
> -static bool running_at_vmpl0(void *va)
> -{
> - u64 attrs;
> -
> - /*
> - * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
> - * higher) privilege level. Here, clear the VMPL1 permission mask of the
> - * GHCB page. If the guest is not running at VMPL0, this will fail.
> - *
> - * If the guest is running at VMPL0, it will succeed. Even if that operation
> - * modifies permission bits, it is still ok to do so currently because Linux
> - * SNP guests running at VMPL0 only run at VMPL0, so VMPL1 or higher
> - * permission mask changes are a don't-care.
> - */
> - attrs = 1;
> - return !rmpadjust((unsigned long)va, RMP_PG_SIZE_4K, attrs);
> -}
> -
> /*
> * SNP_FEATURES_IMPL_REQ is the mask of SNP features that will need
> * guest side implementation for proper functioning of the guest. If any
> @@ -480,6 +472,13 @@ static bool snp_setup(struct boot_params *bp)
> */
> setup_cpuid_table(cc_info);
>
> + /*
> + * Record the SVSM Calling Area address (CAA) if the guest is not
> + * running at VMPL0. The CA will be used to communicate with the
> + * SVSM to perform the SVSM services.
> + */
> + setup_svsm_ca(cc_info);
> +
> /*
> * Pass run-time kernel a pointer to CC info via boot_params so EFI
> * config table doesn't need to be searched again during early startup
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index b463fcbd4b90..68a8cdf6fd6a 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -159,6 +159,10 @@ struct snp_psc_desc {
> #define GHCB_TERM_NOT_VMPL0 3 /* SNP guest is not running at VMPL-0 */
> #define GHCB_TERM_CPUID 4 /* CPUID-validation failure */
> #define GHCB_TERM_CPUID_HV 5 /* CPUID failure during hypervisor fallback */
> +#define GHCB_TERM_SECRETS_PAGE 6 /* Secrets page failure */
> +#define GHCB_TERM_NO_SVSM 7 /* SVSM is not advertised in the secrets page */
> +#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 the CA is not page aligned */
>
> #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 9477b4053bce..891e7d9a1f66 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -152,9 +152,32 @@ struct snp_secrets_page_layout {
> u8 vmpck2[VMPCK_KEY_LEN];
> u8 vmpck3[VMPCK_KEY_LEN];
> struct secrets_os_area os_area;
> - u8 rsvd3[3840];
> +
> + u8 vmsa_tweak_bitmap[64];
> +
> + /* SVSM fields */
> + u64 svsm_base;
> + u64 svsm_size;
> + u64 svsm_caa;
> + u32 svsm_max_version;
> + u8 svsm_guest_vmpl;
> + u8 rsvd3[3];
> +
> + /* Remainder of page */
> + u8 rsvd4[3744];
> } __packed;
>
> +/*
> + * The SVSM Calling Area (CA) related structures.
> + */
> +struct svsm_ca {
> + u8 call_pending;
> + u8 mem_available;
> + u8 rsvd1[6];
> +
> + u8 svsm_buffer[PAGE_SIZE - 8];
> +};
> +
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> extern void __sev_es_ist_enter(struct pt_regs *regs);
> extern void __sev_es_ist_exit(void);
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index 8b04958da5e7..00bb808be44b 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -111,6 +111,24 @@ sev_es_terminate(unsigned int set, unsigned int reason)
> asm volatile("hlt\n" : : : "memory");
> }
>
> +static bool running_at_vmpl0(void *va)
> +{
> + u64 attrs;
> +
> + /*
> + * RMPADJUST modifies RMP permissions of a lesser-privileged (numerically
> + * higher) privilege level. Here, clear the VMPL1 permission mask of the
> + * GHCB page. If the guest is not running at VMPL0, this will fail.
> + *
> + * If the guest is running at VMPL0, it will succeed. Even if that operation
> + * modifies permission bits, it is still ok to do so currently because Linux
> + * SNP guests running at VMPL0 only run at VMPL0, so VMPL1 or higher
> + * permission mask changes are a don't-care.
> + */
> + attrs = 1;
> + return !rmpadjust((unsigned long)va, RMP_PG_SIZE_4K, attrs);
> +}
> +
> /*
> * The hypervisor features are available from GHCB version 2 onward.
> */
> @@ -1267,3 +1285,49 @@ static enum es_result vc_check_opcode_bytes(struct es_em_ctxt *ctxt,
>
> return ES_UNSUPPORTED;
> }
> +
> +/*
> + * Maintain the GPA of the SVSM Calling Area (CA) in order to utilize the SVSM
> + * services needed when not runnuing in VMPL0.
running*
otherwise lgtm
> + */
> +static void __init setup_svsm_ca(const struct cc_blob_sev_info *cc_info)
> +{
> + struct snp_secrets_page_layout *secrets_page;
> + u64 caa;
> +
> + BUILD_BUG_ON(sizeof(*secrets_page) != PAGE_SIZE);
> +
> + /*
> + * Use __pa() since this routine is running identity mapped when
> + * called, both by the decompressor code and the early kernel code.
> + */
> + if (running_at_vmpl0((void *)__pa(&boot_ghcb_page)))
> + return;
> +
> + /*
> + * Not running at VMPL0, ensure everything has been properly supplied
> + * for running under an SVSM.
> + */
> + if (!cc_info || !cc_info->secrets_phys || cc_info->secrets_len != PAGE_SIZE)
> + sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECRETS_PAGE);
> +
> + secrets_page = (struct snp_secrets_page_layout *)cc_info->secrets_phys;
> + if (!secrets_page->svsm_size)
> + sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NO_SVSM);
> +
> + if (!secrets_page->svsm_guest_vmpl)
> + sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_VMPL0);
> +
> + vmpl = secrets_page->svsm_guest_vmpl;
> +
> + caa = secrets_page->svsm_caa;
> + if (!PAGE_ALIGNED(caa))
> + sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CAA);
> +
> + /*
> + * The CA is identity mapped when this routine is called, both by the
> + * decompressor code and the early kernel code.
> + */
> + boot_svsm_caa = (struct svsm_ca *)caa;
> + boot_svsm_caa_pa = caa;
> +}
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index b59b09c2f284..64799a04feb4 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -135,6 +135,15 @@ struct ghcb_state {
> static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
> static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
>
> +/*
> + * SVSM related information:
> + * When running under an SVSM, the VMPL that Linux is executing at must be
> + * non-zero. The VMPL is therefore used to indicate the presence of an SVSM.
> + */
> +static u8 vmpl __ro_after_init;
> +static struct svsm_ca *boot_svsm_caa __ro_after_init;
> +static u64 boot_svsm_caa_pa __ro_after_init;
> +
> struct sev_config {
> __u64 debug : 1,
>
> @@ -2122,6 +2131,13 @@ bool __head snp_init(struct boot_params *bp)
>
> setup_cpuid_table(cc_info);
>
> + /*
> + * Record the SVSM Calling Area address (CAA) if the guest is not
> + * running at VMPL0. The CA will be used to communicate with the
> + * SVSM to perform the SVSM services.
> + */
> + setup_svsm_ca(cc_info);
> +
> /*
> * The CC blob will be used later to access the secrets page. Cache
> * it here like the boot kernel does.
> --
> 2.43.2
>
>
--
-Dionna Glaze, PhD (she/her)
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