[PATCH v2 2/7] KVM: x86: Add helpers to perform CPUID-based guest vendor check

Sean Christopherson
2020-03-05T01:35:08Z

Add helpers to provide CPUID-based guest vendor checks, i.e. to do the
ugly register comparisons. Use the new helpers to check for an AMD
guest vendor in guest_cpuid_is_amd() as well as in the existing emulator
flows.

Using the new helpers fixes a _very_ theoretical bug where
guest_cpuid_is_amd() would get a false positive on a non-AMD virtual CPU
with a vendor string beginning with "Auth" due to the previous logic
only checking EBX. It also fixes a marginally less theoretically bug
where guest_cpuid_is_amd() would incorrectly return false for a guest
CPU with "AMDisbetter!" as its vendor string.

Fixes: a0c0feb57992c ("KVM: x86: reserve bit 8 of non-leaf PDPEs and PML4Es in 64-bit mode on AMD")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
arch/x86/include/asm/kvm_emulate.h | 24 ++++++++++++++++++++
arch/x86/kvm/cpuid.h | 2 +-
arch/x86/kvm/emulate.c | 36 +++++++-----------------------
3 files changed, 33 insertions(+), 29 deletions(-)

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index bf5f5e476f65..2754972c36e6 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -393,6 +393,30 @@ struct x86_emulate_ctxt {
#define X86EMUL_CPUID_VENDOR_GenuineIntel_ecx 0x6c65746e
#define X86EMUL_CPUID_VENDOR_GenuineIntel_edx 0x49656e69

+static inline bool is_guest_vendor_intel(u32 ebx, u32 ecx, u32 edx)
+{
+ return ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
+}
+
+static inline bool is_guest_vendor_amd(u32 ebx, u32 ecx, u32 edx)
+{
+ return (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx) ||
+ (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx);
+}
+
+static inline bool is_guest_vendor_hygon(u32 ebx, u32 ecx, u32 edx)
+{
+ return ebx == X86EMUL_CPUID_VENDOR_HygonGenuine_ebx &&
+ ecx == X86EMUL_CPUID_VENDOR_HygonGenuine_ecx &&
+ edx == X86EMUL_CPUID_VENDOR_HygonGenuine_edx;
+}
+
enum x86_intercept_stage {
X86_ICTP_NONE = 0, /* Allow zero-init to not match anything */
X86_ICPT_PRE_EXCEPT,
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 7366c618aa04..13eb3e92c6a9 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -145,7 +145,7 @@ static inline bool guest_cpuid_is_amd(struct kvm_vcpu *vcpu)
struct kvm_cpuid_entry2 *best;

best = kvm_find_cpuid_entry(vcpu, 0, 0);
- return best && best->ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx;
+ return best && is_guest_vendor_amd(best->ebx, best->ecx, best->edx);
}

static inline int guest_cpuid_family(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index dd19fb3539e0..9cf303984fe5 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2712,9 +2712,7 @@ static bool vendor_intel(struct x86_emulate_ctxt *ctxt)

eax = ecx = 0;
ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
- return ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx
- && ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx
- && edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx;
+ return is_guest_vendor_intel(ebx, ecx, edx);
}

static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
@@ -2733,34 +2731,16 @@ static bool em_syscall_is_enabled(struct x86_emulate_ctxt *ctxt)
ecx = 0x00000000;
ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx, false);
/*
- * Intel ("GenuineIntel")
- * remark: Intel CPUs only support "syscall" in 64bit
- * longmode. Also an 64bit guest with a
- * 32bit compat-app running will #UD !! While this
- * behaviour can be fixed (by emulating) into AMD
- * response - CPUs of AMD can't behave like Intel.
+ * remark: Intel CPUs only support "syscall" in 64bit longmode. Also a
+ * 64bit guest with a 32bit compat-app running will #UD !! While this
+ * behaviour can be fixed (by emulating) into AMD response - CPUs of
+ * AMD can't behave like Intel.
*/
- if (ebx == X86EMUL_CPUID_VENDOR_GenuineIntel_ebx &&
- ecx == X86EMUL_CPUID_VENDOR_GenuineIntel_ecx &&
- edx == X86EMUL_CPUID_VENDOR_GenuineIntel_edx)
+ if (is_guest_vendor_intel(ebx, ecx, edx))
return false;

- /* AMD ("AuthenticAMD") */
- if (ebx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ebx &&
- ecx == X86EMUL_CPUID_VENDOR_AuthenticAMD_ecx &&
- edx == X86EMUL_CPUID_VENDOR_AuthenticAMD_edx)
- return true;
-
- /* AMD ("AMDisbetter!") */
- if (ebx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ebx &&
- ecx == X86EMUL_CPUID_VENDOR_AMDisbetterI_ecx &&
- edx == X86EMUL_CPUID_VENDOR_AMDisbetterI_edx)
- return true;
-
- /* Hygon ("HygonGenuine") */
- if (ebx == X86EMUL_CPUID_VENDOR_HygonGenuine_ebx &&
- ecx == X86EMUL_CPUID_VENDOR_HygonGenuine_ecx &&
- edx == X86EMUL_CPUID_VENDOR_HygonGenuine_edx)
+ if (is_guest_vendor_amd(ebx, ecx, edx) ||
+ is_guest_vendor_hygon(ebx, ecx, edx))
return true;

/*
--
2.24.1