[svsm-devel] [PATCH v5 02/13] x86/sev: Check for the presence of an SVSM in the SNP Secrets page
Tom Lendacky
thomas.lendacky at amd.com
Wed Jun 5 17:18:45 CEST 2024
During early boot phases, check for the presence of an SVSM when running
as an SEV-SNP guest.
An SVSM is present if not running at VMPL0 and 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 at amd.com>
---
.../arch/x86/amd-memory-encryption.rst | 23 ++++++
arch/x86/boot/compressed/sev.c | 21 +++---
arch/x86/include/asm/sev-common.h | 4 ++
arch/x86/include/asm/sev.h | 34 ++++++++-
arch/x86/kernel/sev-shared.c | 71 +++++++++++++++++++
arch/x86/kernel/sev.c | 7 ++
6 files changed, 151 insertions(+), 9 deletions(-)
diff --git a/Documentation/arch/x86/amd-memory-encryption.rst b/Documentation/arch/x86/amd-memory-encryption.rst
index 414bc7402ae7..79eebaa85b7d 100644
--- a/Documentation/arch/x86/amd-memory-encryption.rst
+++ b/Documentation/arch/x86/amd-memory-encryption.rst
@@ -130,4 +130,27 @@ SNP feature support.
More details in AMD64 APM[1] Vol 2: 15.34.10 SEV_STATUS MSR
+Secure VM Service Module (SVSM)
+===============================
+SNP provides a feature called Virtual Machine Privilege Levels (VMPL) which
+defines four privilege levels at which guest software can run. The most
+privileged level is 0 and numerically higher numbers have lesser privileges.
+More details in the AMD64 APM[1] Vol 2, section "15.35.7 Virtual Machine
+Privilege Levels", docID: 24593.
+
+When using that feature, different services can run at different protection
+levels, apart from the guest OS but still within the secure SNP environment.
+They can provide services to the guest, like a vTPM, for example.
+
+When a guest is not running at VMPL0, it needs to communicate with the software
+running at VMPL0 to perform privileged operations or to interact with secure
+services. An example fur such a privileged operation is PVALIDATE which is
+*required* to be executed at VMPL0.
+
+In this scenario, the software running at VMPL0 is usually called a Secure VM
+Service Module (SVSM). Discovery of an SVSM and the API used to communicate
+with it is documented in "Secure VM Service Module for SEV-SNP Guests", docID:
+58019[2].
+
[1] https://www.amd.com/content/dam/amd/en/documents/processor-tech-docs/programmer-references/24593.pdf
+[2] https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 0457a9d7e515..927b71495122 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -462,6 +462,13 @@ static bool early_snp_init(struct boot_params *bp)
*/
setup_cpuid_table(cc_info);
+ /*
+ * Record the SVSM Calling Area (CA) address if the guest is not
+ * running at VMPL0. The CA will be used to communicate with the
+ * SVSM to perform the SVSM services.
+ */
+ svsm_setup_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
@@ -571,14 +578,12 @@ void sev_enable(struct boot_params *bp)
/*
* Enforce running at VMPL0.
*
- * 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.
+ * Use RMPADJUST (see the rmpadjust() function for a description of
+ * what the instruction does) to update the VMPL1 permissions of a
+ * page. If the guest is running at VMPL0, this will succeed. If the
+ * guest is running at any other VMPL, this will fail. Linux SNP guests
+ * only ever run at a single VMPL level so permission mask changes of a
+ * lesser-privileged VMPL are a don't-care.
*/
if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1))
sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 5a8246dd532f..d31f2ed398f0 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -163,6 +163,10 @@ 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 CAA 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 ca20cc4e5826..16d09c1a8ceb 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -152,9 +152,32 @@ struct snp_secrets_page {
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);
@@ -185,6 +208,15 @@ static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long a
{
int rc;
+ /*
+ * RMPADJUST modifies the RMP permissions of a page of a lesser-privileged
+ * (numerically higher) VMPL.
+ *
+ * If the guest is running at a higher-privilege than the privilege level
+ * the instruction is targeting, the instruction will succeed, otherwise,
+ * it will fail.
+ */
+
/* "rmpadjust" mnemonic support in binutils 2.36 and newer */
asm volatile(".byte 0xF3,0x0F,0x01,0xFE\n\t"
: "=a"(rc)
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index b4f8fa0f722c..739362066e00 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -23,6 +23,21 @@
#define sev_printk_rtl(fmt, ...)
#endif
+/*
+ * 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.
+ *
+ * During boot, the page tables are set up as identity mapped and later
+ * changed to use kernel virtual addresses. Maintain separate virtual and
+ * physical addresses for the CAA to allow SVSM functions to be used during
+ * early boot, both with identity mapped virtual addresses and proper kernel
+ * virtual addresses.
+ */
+static u8 snp_vmpl __ro_after_init;
+static struct svsm_ca *boot_svsm_caa __ro_after_init;
+static u64 boot_svsm_caa_pa __ro_after_init;
+
/* I/O parameters for CPUID-related helpers */
struct cpuid_leaf {
u32 fn;
@@ -1269,3 +1284,59 @@ 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 running in VMPL0.
+ */
+static void __head svsm_setup_ca(const struct cc_blob_sev_info *cc_info)
+{
+ struct snp_secrets_page *secrets_page;
+ u64 caa;
+
+ BUILD_BUG_ON(sizeof(*secrets_page) != PAGE_SIZE);
+
+ /*
+ * Check if running at VMPL0.
+ *
+ * Use RMPADJUST (see the rmpadjust() function for a description of what
+ * the instruction does) to update the VMPL1 permissions of a page. If
+ * the guest is running at VMPL0, this will succeed and implies there is
+ * no SVSM. If the guest is running at any other VMPL, this will fail.
+ * Linux SNP guests only ever run at a single VMPL level so permission mask
+ * changes of a lesser-privileged VMPL are a don't-care.
+ *
+ * Use a rip-relative reference to obtain the proper address, since this
+ * routine is running identity mapped when called, both by the decompressor
+ * code and the early kernel code.
+ */
+ if (!rmpadjust((unsigned long)&RIP_REL_REF(boot_ghcb_page), RMP_PG_SIZE_4K, 1))
+ 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 *)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);
+
+ RIP_REL_REF(snp_vmpl) = secrets_page->svsm_guest_vmpl;
+
+ caa = secrets_page->svsm_caa;
+ if (caa & (PAGE_SIZE - 1))
+ 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.
+ */
+ RIP_REL_REF(boot_svsm_caa) = (struct svsm_ca *)caa;
+ RIP_REL_REF(boot_svsm_caa_pa) = caa;
+}
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 3342ed58e168..36a117a38b10 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2108,6 +2108,13 @@ 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.
+ */
+ svsm_setup_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
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