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Date: Wed, 5 Jun 2024 10:18:51 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
<linux-coco@...ts.linux.dev>, <svsm-devel@...onut-svsm.dev>
CC: 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: [PATCH v5 08/13] virt: sev-guest: Choose the VMPCK key based on executing VMPL
Currently, the sev-guest driver uses the vmpck-0 key by default. When an
SVSM is present, the kernel is running at a VMPL other than 0 and the
vmpck-0 key is no longer available. If a specific vmpck key has not be
requested by the user via the vmpck_id module parameter, choose the vmpck
key based on the active VMPL level.
Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
Documentation/virt/coco/sev-guest.rst | 11 +++++++++++
arch/x86/include/asm/sev.h | 11 +++++++++--
arch/x86/kernel/sev-shared.c | 3 ++-
drivers/virt/coco/sev-guest/sev-guest.c | 17 ++++++++++++++---
4 files changed, 36 insertions(+), 6 deletions(-)
diff --git a/Documentation/virt/coco/sev-guest.rst b/Documentation/virt/coco/sev-guest.rst
index e1eaf6a830ce..9d00967a5b2b 100644
--- a/Documentation/virt/coco/sev-guest.rst
+++ b/Documentation/virt/coco/sev-guest.rst
@@ -204,6 +204,17 @@ has taken care to make use of the SEV-SNP CPUID throughout all stages of boot.
Otherwise, guest owner attestation provides no assurance that the kernel wasn't
fed incorrect values at some point during boot.
+4. SEV Guest Driver Communication Key
+=====================================
+
+Communication between an SEV guest and the SEV firmware in the AMD Secure
+Processor (ASP, aka PSP) is protected by a VM Platform Communication Key
+(VMPCK). By default, the sev-guest driver uses the VMPCK associated with the
+VM Privilege Level (VMPL) at which the guest is running. Should this key be
+wiped by the sev-guest driver (see the driver for reasons why a VMPCK can be
+wiped), a different key can be used by reloading the sev-guest driver and
+specifying the desired key using the vmpck_id module parameter.
+
Reference
---------
diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 36cd7aebaa9b..f7a966e99a73 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -237,6 +237,9 @@ struct svsm_call {
#define SVSM_CORE_DELETE_VCPU 3
#ifdef CONFIG_AMD_MEM_ENCRYPT
+
+extern u8 snp_vmpl;
+
extern void __sev_es_ist_enter(struct pt_regs *regs);
extern void __sev_es_ist_exit(void);
static __always_inline void sev_es_ist_enter(struct pt_regs *regs)
@@ -320,7 +323,10 @@ u64 snp_get_unsupported_features(u64 status);
u64 sev_get_status(void);
void sev_show_status(void);
void snp_remap_svsm_ca(void);
-#else
+
+#else /* !CONFIG_AMD_MEM_ENCRYPT */
+
+#define snp_vmpl 0
static inline void sev_es_ist_enter(struct pt_regs *regs) { }
static inline void sev_es_ist_exit(void) { }
static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { return 0; }
@@ -350,7 +356,8 @@ static inline u64 snp_get_unsupported_features(u64 status) { return 0; }
static inline u64 sev_get_status(void) { return 0; }
static inline void sev_show_status(void) { }
static inline void snp_remap_svsm_ca(void) { }
-#endif
+
+#endif /* CONFIG_AMD_MEM_ENCRYPT */
#ifdef CONFIG_KVM_AMD_SEV
bool snp_probe_rmptable_info(void);
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index e91fcffcf602..10599e66c5fd 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -36,7 +36,8 @@
* early boot, both with identity mapped virtual addresses and proper kernel
* virtual addresses.
*/
-static u8 snp_vmpl __ro_after_init;
+u8 snp_vmpl __ro_after_init;
+EXPORT_SYMBOL_GPL(snp_vmpl);
static struct svsm_ca *boot_svsm_caa __ro_after_init;
static u64 boot_svsm_caa_pa __ro_after_init;
diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
index 654290a8e1ba..4597042f31e4 100644
--- a/drivers/virt/coco/sev-guest/sev-guest.c
+++ b/drivers/virt/coco/sev-guest/sev-guest.c
@@ -2,7 +2,7 @@
/*
* AMD Secure Encrypted Virtualization (SEV) guest driver interface
*
- * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ * Copyright (C) 2021-2024 Advanced Micro Devices, Inc.
*
* Author: Brijesh Singh <brijesh.singh@....com>
*/
@@ -70,8 +70,15 @@ struct snp_guest_dev {
u8 *vmpck;
};
-static u32 vmpck_id;
-module_param(vmpck_id, uint, 0444);
+/*
+ * The VMPCK ID represents the key used by the SNP guest to communicate with the
+ * SEV firmware in the AMD Secure Processor (ASP, aka PSP). By default, the key
+ * used will be the key associated with the VMPL at which the guest is running.
+ * Should the default key be wiped (see snp_disable_vmpck()), this parameter
+ * allows for using one of the remaining VMPCKs.
+ */
+static int vmpck_id = -1;
+module_param(vmpck_id, int, 0444);
MODULE_PARM_DESC(vmpck_id, "The VMPCK ID to use when communicating with the PSP.");
/* Mutex to serialize the shared buffer access and command handling. */
@@ -923,6 +930,10 @@ static int __init sev_guest_probe(struct platform_device *pdev)
if (!snp_dev)
goto e_unmap;
+ /* Adjust the default VMPCK key based on the executing VMPL level */
+ if (vmpck_id == -1)
+ vmpck_id = snp_vmpl;
+
ret = -EINVAL;
snp_dev->vmpck = get_vmpck(vmpck_id, secrets, &snp_dev->os_area_msg_seqno);
if (!snp_dev->vmpck) {
--
2.43.2
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