[PATCH v8 34/40] x86/sev: add SEV-SNP feature detection/setup

Brijesh Singh
2021-12-10T15:46:46Z

From: Michael Roth <michael.roth@amd.com>

Initial/preliminary detection of SEV-SNP is done via the Confidential
Computing blob. Check for it prior to the normal SEV/SME feature
initialization, and add some sanity checks to confirm it agrees with
SEV-SNP CPUID/MSR bits.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
arch/x86/include/asm/sev.h | 3 +-
arch/x86/kernel/sev-shared.c | 2 +-
arch/x86/kernel/sev.c | 65 ++++++++++++++++++++++++++++++
arch/x86/mm/mem_encrypt_identity.c | 8 ++++
4 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 4fa7ca20d7c9..4d32af1348ed 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -147,6 +147,7 @@ void snp_set_memory_shared(unsigned long vaddr, unsigned int npages);
void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
void snp_set_wakeup_secondary_cpu(void);
bool snp_init(struct boot_params *bp);
+void snp_abort(void);
/*
* TODO: These are exported only temporarily while boot/compressed/sev.c is
* the only user. This is to avoid unused function warnings for kernel/sev.c
@@ -156,7 +157,6 @@ bool snp_init(struct boot_params *bp);
* can be moved back to being statically-scoped to units that pull in
* sev-shared.c via #include and these declarations can be dropped.
*/
-struct cc_blob_sev_info *snp_find_cc_blob_setup_data(struct boot_params *bp);
void snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info);
#else
static inline void sev_es_ist_enter(struct pt_regs *regs) { }
@@ -176,6 +176,7 @@ static inline void snp_set_memory_shared(unsigned long vaddr, unsigned int npage
static inline void snp_set_memory_private(unsigned long vaddr, unsigned int npages) { }
static inline void snp_set_wakeup_secondary_cpu(void) { }
static inline bool snp_init(struct boot_params *bp) { return false; }
+static inline void snp_abort(void) { }
#endif

#endif
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 5cb8f87df4b3..72836abcdbe2 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -974,7 +974,7 @@ static struct cc_setup_data *get_cc_setup_data(struct boot_params *bp)
* Search for a Confidential Computing blob passed in as a setup_data entry
* via the Linux Boot Protocol.
*/
-struct cc_blob_sev_info *
+static struct cc_blob_sev_info *
snp_find_cc_blob_setup_data(struct boot_params *bp)
{
struct cc_setup_data *sd;
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 32f60602ec29..0e5c45eacc77 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1949,3 +1949,68 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
while (true)
halt();
}
+
+/*
+ * Initial set up of SEV-SNP relies on information provided by the
+ * Confidential Computing blob, which can be passed to the kernel
+ * in the following ways, depending on how it is booted:
+ *
+ * - when booted via the boot/decompress kernel:
+ * - via boot_params
+ *
+ * - when booted directly by firmware/bootloader (e.g. CONFIG_PVH):
+ * - via a setup_data entry, as defined by the Linux Boot Protocol
+ *
+ * Scan for the blob in that order.
+ */
+static struct cc_blob_sev_info *snp_find_cc_blob(struct boot_params *bp)
+{
+ struct cc_blob_sev_info *cc_info;
+
+ /* Boot kernel would have passed the CC blob via boot_params. */
+ if (bp->cc_blob_address) {
+ cc_info = (struct cc_blob_sev_info *)
+ (unsigned long)bp->cc_blob_address;
+ goto found_cc_info;
+ }
+
+ /*
+ * If kernel was booted directly, without the use of the
+ * boot/decompression kernel, the CC blob may have been passed via
+ * setup_data instead.
+ */
+ cc_info = snp_find_cc_blob_setup_data(bp);
+ if (!cc_info)
+ return NULL;
+
+found_cc_info:
+ if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
+ sev_es_terminate(1, GHCB_SNP_UNSUPPORTED);
+
+ return cc_info;
+}
+
+bool __init snp_init(struct boot_params *bp)
+{
+ struct cc_blob_sev_info *cc_info;
+
+ if (!bp)
+ return false;
+
+ cc_info = snp_find_cc_blob(bp);
+ if (!cc_info)
+ return false;
+
+ /*
+ * The CC blob will be used later to access the secrets page. Cache
+ * it here like the boot kernel does.
+ */
+ bp->cc_blob_address = (u32)(unsigned long)cc_info;
+
+ return true;
+}
+
+void __init snp_abort(void)
+{
+ sev_es_terminate(1, GHCB_SNP_UNSUPPORTED);
+}
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 3f0abb403340..2f723e106ed3 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -44,6 +44,7 @@
#include <asm/setup.h>
#include <asm/sections.h>
#include <asm/cmdline.h>
+#include <asm/sev.h>

#include "mm_internal.h"

@@ -508,8 +509,11 @@ void __init sme_enable(struct boot_params *bp)
bool active_by_default;
unsigned long me_mask;
char buffer[16];
+ bool snp;
u64 msr;

+ snp = snp_init(bp);
+
/* Check for the SME/SEV support leaf */
eax = 0x80000000;
ecx = 0;
@@ -541,6 +545,10 @@ void __init sme_enable(struct boot_params *bp)
sev_status = __rdmsr(MSR_AMD64_SEV);
feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;

+ /* The SEV-SNP CC blob should never be present unless SEV-SNP is enabled. */
+ if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+ snp_abort();
+
/* Check if memory encryption is enabled */
if (feature_mask == AMD_SME_BIT) {
/*
--
2.25.1