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From: Tom Lendacky <thomas.lendacky@amd.com>
To: <linux-kernel@vger.kernel.org>, <x86@kernel.org>,
	<linux-coco@lists.linux.dev>, <svsm-devel@coconut-svsm.dev>
CC: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Andy Lutomirski <luto@kernel.org>, "Peter
 Zijlstra" <peterz@infradead.org>, Dan Williams <dan.j.williams@intel.com>,
	Michael Roth <michael.roth@amd.com>, Ashish Kalra <ashish.kalra@amd.com>
Subject: [PATCH v3 03/14] x86/sev: Check for the presence of an SVSM in the SNP Secrets page
Date: Mon, 25 Mar 2024 17:26:22 -0500
Message-ID: <e8d4877f3b7248031931ed193c026c42dd3363ef.1711405593.git.thomas.lendacky@amd.com>
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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@amd.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 49dc9661176d..fe61ff630c7e 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 early_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);
+
 	/*
 	 * 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..66d33292eb78 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 running in VMPL0.
+ */
+static void __head 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