* [PATCH 1/2] x86/boot: Move boot_*msr helpers to asm/shared/msr.h
2025-08-06 20:46 [PATCH 0/2] Support for SEV-ES guest shadow stack John Allen
@ 2025-08-06 20:46 ` John Allen
2025-08-08 18:07 ` Tom Lendacky
2025-08-06 20:46 ` [PATCH 2/2] x86/sev-es: Include XSS value in GHCB CPUID request John Allen
1 sibling, 1 reply; 5+ messages in thread
From: John Allen @ 2025-08-06 20:46 UTC (permalink / raw)
To: kvm, linux-kernel, x86, seanjc, pbonzini, dave.hansen
Cc: rick.p.edgecombe, mlevitsk, weijiang.yang, chao.gao, bp,
dave.hansen, hpa, mingo, tglx, thomas.lendacky, John Allen
The boot_rdmsr and boot_wrmsr helpers used to reduce the need for inline
assembly in the boot kernel can also be useful in code shared by boot
and run-time kernel code. Move these helpers to asm/shared/msr.h and
rename to raw_rdmsr and raw_wrmsr to indicate that these may also be
used outside of the boot kernel.
Signed-off-by: John Allen <john.allen@amd.com>
---
arch/x86/boot/compressed/sev.c | 7 ++++---
arch/x86/boot/compressed/sev.h | 6 +++---
arch/x86/boot/cpucheck.c | 16 ++++++++--------
arch/x86/boot/msr.h | 26 --------------------------
arch/x86/include/asm/shared/msr.h | 15 +++++++++++++++
5 files changed, 30 insertions(+), 40 deletions(-)
delete mode 100644 arch/x86/boot/msr.h
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index fd1b67dfea22..250b7156bd0f 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -14,6 +14,7 @@
#include <asm/bootparam.h>
#include <asm/pgtable_types.h>
+#include <asm/shared/msr.h>
#include <asm/sev.h>
#include <asm/trapnr.h>
#include <asm/trap_pf.h>
@@ -436,7 +437,7 @@ void sev_enable(struct boot_params *bp)
}
/* Set the SME mask if this is an SEV guest. */
- boot_rdmsr(MSR_AMD64_SEV, &m);
+ raw_rdmsr(MSR_AMD64_SEV, &m);
sev_status = m.q;
if (!(sev_status & MSR_AMD64_SEV_ENABLED))
return;
@@ -499,7 +500,7 @@ u64 sev_get_status(void)
if (sev_check_cpu_support() < 0)
return 0;
- boot_rdmsr(MSR_AMD64_SEV, &m);
+ raw_rdmsr(MSR_AMD64_SEV, &m);
return m.q;
}
@@ -549,7 +550,7 @@ bool early_is_sevsnp_guest(void)
struct msr m;
/* Obtain the address of the calling area to use */
- boot_rdmsr(MSR_SVSM_CAA, &m);
+ raw_rdmsr(MSR_SVSM_CAA, &m);
boot_svsm_caa = (void *)m.q;
boot_svsm_caa_pa = m.q;
diff --git a/arch/x86/boot/compressed/sev.h b/arch/x86/boot/compressed/sev.h
index 92f79c21939c..81766d002c0a 100644
--- a/arch/x86/boot/compressed/sev.h
+++ b/arch/x86/boot/compressed/sev.h
@@ -10,7 +10,7 @@
#ifdef CONFIG_AMD_MEM_ENCRYPT
-#include "../msr.h"
+#include "asm/shared/msr.h"
void snp_accept_memory(phys_addr_t start, phys_addr_t end);
u64 sev_get_status(void);
@@ -20,7 +20,7 @@ static inline u64 sev_es_rd_ghcb_msr(void)
{
struct msr m;
- boot_rdmsr(MSR_AMD64_SEV_ES_GHCB, &m);
+ raw_rdmsr(MSR_AMD64_SEV_ES_GHCB, &m);
return m.q;
}
@@ -30,7 +30,7 @@ static inline void sev_es_wr_ghcb_msr(u64 val)
struct msr m;
m.q = val;
- boot_wrmsr(MSR_AMD64_SEV_ES_GHCB, &m);
+ raw_wrmsr(MSR_AMD64_SEV_ES_GHCB, &m);
}
#else
diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
index f82de8de5dc6..2e1bb936cba2 100644
--- a/arch/x86/boot/cpucheck.c
+++ b/arch/x86/boot/cpucheck.c
@@ -26,9 +26,9 @@
#include <asm/intel-family.h>
#include <asm/processor-flags.h>
#include <asm/msr-index.h>
+#include <asm/shared/msr.h>
#include "string.h"
-#include "msr.h"
static u32 err_flags[NCAPINTS];
@@ -134,9 +134,9 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
struct msr m;
- boot_rdmsr(MSR_K7_HWCR, &m);
+ raw_rdmsr(MSR_K7_HWCR, &m);
m.l &= ~(1 << 15);
- boot_wrmsr(MSR_K7_HWCR, &m);
+ raw_wrmsr(MSR_K7_HWCR, &m);
get_cpuflags(); /* Make sure it really did something */
err = check_cpuflags();
@@ -148,9 +148,9 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
struct msr m;
- boot_rdmsr(MSR_VIA_FCR, &m);
+ raw_rdmsr(MSR_VIA_FCR, &m);
m.l |= (1 << 1) | (1 << 7);
- boot_wrmsr(MSR_VIA_FCR, &m);
+ raw_wrmsr(MSR_VIA_FCR, &m);
set_bit(X86_FEATURE_CX8, cpu.flags);
err = check_cpuflags();
@@ -160,14 +160,14 @@ int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr)
struct msr m, m_tmp;
u32 level = 1;
- boot_rdmsr(0x80860004, &m);
+ raw_rdmsr(0x80860004, &m);
m_tmp = m;
m_tmp.l = ~0;
- boot_wrmsr(0x80860004, &m_tmp);
+ raw_wrmsr(0x80860004, &m_tmp);
asm("cpuid"
: "+a" (level), "=d" (cpu.flags[0])
: : "ecx", "ebx");
- boot_wrmsr(0x80860004, &m);
+ raw_wrmsr(0x80860004, &m);
err = check_cpuflags();
} else if (err == 0x01 &&
diff --git a/arch/x86/boot/msr.h b/arch/x86/boot/msr.h
deleted file mode 100644
index aed66f7ae199..000000000000
--- a/arch/x86/boot/msr.h
+++ /dev/null
@@ -1,26 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Helpers/definitions related to MSR access.
- */
-
-#ifndef BOOT_MSR_H
-#define BOOT_MSR_H
-
-#include <asm/shared/msr.h>
-
-/*
- * The kernel proper already defines rdmsr()/wrmsr(), but they are not for the
- * boot kernel since they rely on tracepoint/exception handling infrastructure
- * that's not available here.
- */
-static inline void boot_rdmsr(unsigned int reg, struct msr *m)
-{
- asm volatile("rdmsr" : "=a" (m->l), "=d" (m->h) : "c" (reg));
-}
-
-static inline void boot_wrmsr(unsigned int reg, const struct msr *m)
-{
- asm volatile("wrmsr" : : "c" (reg), "a"(m->l), "d" (m->h) : "memory");
-}
-
-#endif /* BOOT_MSR_H */
diff --git a/arch/x86/include/asm/shared/msr.h b/arch/x86/include/asm/shared/msr.h
index 1e6ec10b3a15..a20b1c08c99f 100644
--- a/arch/x86/include/asm/shared/msr.h
+++ b/arch/x86/include/asm/shared/msr.h
@@ -12,4 +12,19 @@ struct msr {
};
};
+/*
+ * The kernel proper already defines rdmsr()/wrmsr(), but they are not for the
+ * boot kernel since they rely on tracepoint/exception handling infrastructure
+ * that's not available here.
+ */
+static inline void raw_rdmsr(unsigned int reg, struct msr *m)
+{
+ asm volatile("rdmsr" : "=a" (m->l), "=d" (m->h) : "c" (reg));
+}
+
+static inline void raw_wrmsr(unsigned int reg, const struct msr *m)
+{
+ asm volatile("wrmsr" : : "c" (reg), "a"(m->l), "d" (m->h) : "memory");
+}
+
#endif /* _ASM_X86_SHARED_MSR_H */
--
2.34.1
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH 2/2] x86/sev-es: Include XSS value in GHCB CPUID request
2025-08-06 20:46 [PATCH 0/2] Support for SEV-ES guest shadow stack John Allen
2025-08-06 20:46 ` [PATCH 1/2] x86/boot: Move boot_*msr helpers to asm/shared/msr.h John Allen
@ 2025-08-06 20:46 ` John Allen
2025-08-08 18:13 ` Tom Lendacky
1 sibling, 1 reply; 5+ messages in thread
From: John Allen @ 2025-08-06 20:46 UTC (permalink / raw)
To: kvm, linux-kernel, x86, seanjc, pbonzini, dave.hansen
Cc: rick.p.edgecombe, mlevitsk, weijiang.yang, chao.gao, bp,
dave.hansen, hpa, mingo, tglx, thomas.lendacky, John Allen
When a guest issues a cpuid instruction for Fn0000000D_x0B
(CetUserOffset), the hypervisor may intercept and access the guest XSS
value. For SEV-ES, this is encrypted and needs to be included in the
GHCB to be visible to the hypervisor.
Signed-off-by: John Allen <john.allen@amd.com>
---
arch/x86/coco/sev/vc-shared.c | 11 +++++++++++
arch/x86/include/asm/svm.h | 1 +
2 files changed, 12 insertions(+)
diff --git a/arch/x86/coco/sev/vc-shared.c b/arch/x86/coco/sev/vc-shared.c
index 2c0ab0fdc060..079fffdb12c0 100644
--- a/arch/x86/coco/sev/vc-shared.c
+++ b/arch/x86/coco/sev/vc-shared.c
@@ -1,5 +1,9 @@
// SPDX-License-Identifier: GPL-2.0
+#ifndef __BOOT_COMPRESSED
+#define has_cpuflag(f) boot_cpu_has(f)
+#endif
+
static enum es_result vc_check_opcode_bytes(struct es_em_ctxt *ctxt,
unsigned long exit_code)
{
@@ -452,6 +456,13 @@ static enum es_result vc_handle_cpuid(struct ghcb *ghcb,
/* xgetbv will cause #GP - use reset value for xcr0 */
ghcb_set_xcr0(ghcb, 1);
+ if (has_cpuflag(X86_FEATURE_SHSTK) && regs->ax == 0xd && regs->cx <= 1) {
+ struct msr m;
+
+ raw_rdmsr(MSR_IA32_XSS, &m);
+ ghcb_set_xss(ghcb, m.q);
+ }
+
ret = sev_es_ghcb_hv_call(ghcb, ctxt, SVM_EXIT_CPUID, 0, 0);
if (ret != ES_OK)
return ret;
diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index ffc27f676243..870ebfef86d6 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -700,5 +700,6 @@ DEFINE_GHCB_ACCESSORS(sw_exit_info_1)
DEFINE_GHCB_ACCESSORS(sw_exit_info_2)
DEFINE_GHCB_ACCESSORS(sw_scratch)
DEFINE_GHCB_ACCESSORS(xcr0)
+DEFINE_GHCB_ACCESSORS(xss)
#endif
--
2.34.1
^ permalink raw reply [flat|nested] 5+ messages in thread