The following commit has been merged into the x86/sev branch of tip:
Commit-ID: 81cc3df9a90e7817494421ecc48ede6bd5e8132b
Gitweb: https://git.kernel.org/tip/81cc3df9a90e7817494421ecc48ede6bd5e8132b
Author: Brijesh Singh <brijesh.singh@xxxxxxx>
AuthorDate: Wed, 09 Feb 2022 12:10:08 -06:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Wed, 06 Apr 2022 13:10:34 +02:00
x86/sev: Check the VMPL level
The Virtual Machine Privilege Level (VMPL) feature in the SEV-SNP
architecture allows a guest VM to divide its address space into four
levels. The level can be used to provide hardware isolated abstraction
layers within a VM. VMPL0 is the highest privilege level, and VMPL3 is
the least privilege level. Certain operations must be done by the VMPL0
software, such as:
* Validate or invalidate memory range (PVALIDATE instruction)
* Allocate VMSA page (RMPADJUST instruction when VMSA=1)
The initial SNP support requires that the guest kernel is running at
VMPL0. Add such a check to verify the guest is running at level 0 before
continuing the boot. There is no easy method to query the current VMPL
level, so use the RMPADJUST instruction to determine whether the guest
is running at the VMPL0.
[ bp: Massage commit message. ]
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lore.kernel.org/r/20220307213356.2797205-15-brijesh.singh@xxxxxxx
---
arch/x86/boot/compressed/sev.c | 28 ++++++++++++++++++++++++++--
arch/x86/include/asm/sev-common.h | 1 +
arch/x86/include/asm/sev.h | 16 ++++++++++++++++
3 files changed, 43 insertions(+), 2 deletions(-)
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 5b38931..eb42178 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -199,6 +199,26 @@ finish:
sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_GEN_REQ);
}
+static void enforce_vmpl0(void)
+{
+ u64 attrs;
+ int err;
+
+ /*
+ * 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 are supported only on VMPL0 so VMPL1 or higher permission masks
+ * changing is a don't-care.
+ */
+ attrs = 1;
+ if (rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, attrs))
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
+}
+
void sev_enable(struct boot_params *bp)
{
unsigned int eax, ebx, ecx, edx;
@@ -242,8 +262,12 @@ void sev_enable(struct boot_params *bp)
* SNP is supported in v2 of the GHCB spec which mandates support for HV
* features.
*/
- if (sev_status & MSR_AMD64_SEV_SNP_ENABLED && !(get_hv_features() & GHCB_HV_FT_SNP))
- sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+ if (sev_status & MSR_AMD64_SEV_SNP_ENABLED) {
+ if (!(get_hv_features() & GHCB_HV_FT_SNP))
+ sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
+
+ enforce_vmpl0();
+ }
sme_me_mask = BIT_ULL(ebx & 0x3f);
}
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index 6f037c2..7ac5842 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -89,6 +89,7 @@
#define GHCB_TERM_REGISTER 0 /* GHCB GPA registration failure */
#define GHCB_TERM_PSC 1 /* Page State Change failure */
#define GHCB_TERM_PVALIDATE 2 /* Pvalidate failure */
+#define GHCB_TERM_NOT_VMPL0 3 /* SNP guest is not running at VMPL-0 */
#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 4ee9897..e374518 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -63,6 +63,9 @@ extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
/* Software defined (when rFlags.CF = 1) */
#define PVALIDATE_FAIL_NOUPDATE 255
+/* RMP page size */
+#define RMP_PG_SIZE_4K 0
+
#ifdef CONFIG_AMD_MEM_ENCRYPT
extern struct static_key_false sev_es_enable_key;
extern void __sev_es_ist_enter(struct pt_regs *regs);
@@ -90,6 +93,18 @@ extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
struct es_em_ctxt *ctxt,
u64 exit_code, u64 exit_info_1,
u64 exit_info_2);
+static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs)
+{
+ int rc;
+
+ /* "rmpadjust" mnemonic support in binutils 2.36 and newer */
+ asm volatile(".byte 0xF3,0x0F,0x01,0xFE\n\t"
+ : "=a"(rc)
+ : "a"(vaddr), "c"(rmp_psize), "d"(attrs)
+ : "memory", "cc");
+
+ return rc;
+}
static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate)
{
bool no_rmpupdate;
@@ -114,6 +129,7 @@ static inline int sev_es_setup_ap_jump_table(struct real_mode_header *rmh) { ret
static inline void sev_es_nmi_complete(void) { }
static inline int sev_es_efi_map_ghcbs(pgd_t *pgd) { return 0; }
static inline int pvalidate(unsigned long vaddr, bool rmp_psize, bool validate) { return 0; }
+static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs) { return 0; }
#endif
#endif
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