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Date: Fri, 5 Jan 2024 11:14:07 +0100
From: Borislav Petkov <bp@...en8.de>
To: X86 ML <x86@...nel.org>
Cc: Tom Lendacky <thomas.lendacky@....com>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/sev: Harden #VC insn emulation somewhat
From: "Borislav Petkov (AMD)" <bp@...en8.de>
Compare the opcode bytes at rIP for each #VC exit reason to verify the
instruction which raised the #VC exception is actually the right one.
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
arch/x86/boot/compressed/sev.c | 4 ++
arch/x86/kernel/sev-shared.c | 102 ++++++++++++++++++++++++++++++++-
arch/x86/kernel/sev.c | 9 ++-
3 files changed, 108 insertions(+), 7 deletions(-)
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 454acd7a2daf..073291832f44 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -304,6 +304,10 @@ void do_boot_stage2_vc(struct pt_regs *regs, unsigned long exit_code)
if (result != ES_OK)
goto finish;
+ result = vc_check_opcode_bytes(&ctxt, exit_code);
+ if (result != ES_OK)
+ goto finish;
+
switch (exit_code) {
case SVM_EXIT_RDTSC:
case SVM_EXIT_RDTSCP:
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index ccb0915e84e1..ec17931bf3cd 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -10,11 +10,15 @@
*/
#ifndef __BOOT_COMPRESSED
-#define error(v) pr_err(v)
-#define has_cpuflag(f) boot_cpu_has(f)
+#define error(v) pr_err(v)
+#define has_cpuflag(f) boot_cpu_has(f)
+#define sev_printk(fmt, ...) printk(fmt, ##__VA_ARGS__)
+#define sev_printk_rtl(fmt, ...) printk_ratelimited(fmt, ##__VA_ARGS__)
#else
#undef WARN
#define WARN(condition, format...) (!!(condition))
+#define sev_printk(fmt, ...)
+#define sev_printk_rtl(fmt, ...)
#endif
/* I/O parameters for CPUID-related helpers */
@@ -574,6 +578,7 @@ void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
{
unsigned int subfn = lower_bits(regs->cx, 32);
unsigned int fn = lower_bits(regs->ax, 32);
+ u16 opcode = *(unsigned short *)regs->ip;
struct cpuid_leaf leaf;
int ret;
@@ -581,6 +586,10 @@ void __init do_vc_no_ghcb(struct pt_regs *regs, unsigned long exit_code)
if (exit_code != SVM_EXIT_CPUID)
goto fail;
+ /* Is it really a CPUID insn? */
+ if (opcode != 0xa20f)
+ goto fail;
+
leaf.fn = fn;
leaf.subfn = subfn;
@@ -1170,3 +1179,92 @@ static int vmgexit_psc(struct ghcb *ghcb, struct snp_psc_desc *desc)
out:
return ret;
}
+
+static enum es_result vc_check_opcode_bytes(struct es_em_ctxt *ctxt,
+ unsigned long exit_code)
+{
+ unsigned int opcode = (unsigned int)ctxt->insn.opcode.value;
+ u8 modrm = ctxt->insn.modrm.value;
+
+ switch (exit_code) {
+
+ case SVM_EXIT_IOIO:
+ case SVM_EXIT_NPF:
+ /* handled separately */
+ return ES_OK;
+
+ case SVM_EXIT_CPUID:
+ if (opcode == 0xa20f)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_INVD:
+ sev_printk_rtl(KERN_ERR "#VC exception for INVD??? Seriously???\n");
+ return ES_UNSUPPORTED;
+ break;
+
+ case SVM_EXIT_MONITOR:
+ if (opcode == 0x010f && modrm == 0xc8)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_MWAIT:
+ if (opcode == 0x010f && modrm == 0xc9)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_MSR:
+ /* RDMSR */
+ if (opcode == 0x320f ||
+ /* WRMSR */
+ opcode == 0x300f)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_RDPMC:
+ if (opcode == 0x330f)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_RDTSC:
+ if (opcode == 0x310f)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_RDTSCP:
+ if (opcode == 0x010f && modrm == 0xf9)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_READ_DR7:
+ if (opcode == 0x210f &&
+ X86_MODRM_REG(ctxt->insn.modrm.value) == 7)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_VMMCALL:
+ if (opcode == 0x010f && modrm == 0xd9)
+ return ES_OK;
+
+ break;
+
+ case SVM_EXIT_WRITE_DR7:
+ if (opcode == 0x230f &&
+ X86_MODRM_REG(ctxt->insn.modrm.value) == 7)
+ return ES_OK;
+ break;
+
+ case SVM_EXIT_WBINVD:
+ if (opcode == 0x90f)
+ return ES_OK;
+ break;
+
+ default:
+ break;
+ }
+
+ sev_printk(KERN_ERR "Wrong/unhandled opcode bytes: 0x%x, exit_code: 0x%lx, rIP: 0x%lx\n",
+ opcode, exit_code, ctxt->regs->ip);
+
+ return ES_UNSUPPORTED;
+}
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index c67285824e82..541a1f87b4f1 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -1752,7 +1752,10 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
struct ghcb *ghcb,
unsigned long exit_code)
{
- enum es_result result;
+ enum es_result result = vc_check_opcode_bytes(ctxt, exit_code);
+
+ if (result != ES_OK)
+ return result;
switch (exit_code) {
case SVM_EXIT_READ_DR7:
@@ -1771,10 +1774,6 @@ static enum es_result vc_handle_exitcode(struct es_em_ctxt *ctxt,
case SVM_EXIT_RDPMC:
result = vc_handle_rdpmc(ghcb, ctxt);
break;
- case SVM_EXIT_INVD:
- pr_err_ratelimited("#VC exception for INVD??? Seriously???\n");
- result = ES_UNSUPPORTED;
- break;
case SVM_EXIT_CPUID:
result = vc_handle_cpuid(ghcb, ctxt);
break;
--
2.42.0.rc0.25.ga82fb66fed25
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