Add compile-time assertions to verify that usage of F() and friends in
kvm_set_cpu_caps() is scoped to the correct CPUID word, e.g. to detect
bugs where KVM passes a feature bit from word X into word y.
Add a one-off assertion in the aliased feature macro to ensure that only
word 0x8000_0001.EDX aliased the features defined for 0x1.EDX.
To do so, convert kvm_cpu_cap_init() to a macro and have it define a
local variable to track which CPUID word is being initialized that is
then used to validate usage of F() (all of the inputs are compile-time
constants and thus can be fed into BUILD_BUG_ON()).
Redefine KVM_VALIDATE_CPU_CAP_USAGE after kvm_set_cpu_caps() to be a nop
so that F() can be used in other flows that aren't as easily hardened,
e.g. __do_cpuid_func_emulated() and __do_cpuid_func().
Invoke KVM_VALIDATE_CPU_CAP_USAGE() in SF() and X86_64_F() to ensure the
validation occurs, e.g. if the usage of F() is completely compiled out
(which shouldn't happen for boot_cpu_has(), but could happen in the future,
e.g. if KVM were to use cpu_feature_enabled()).
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/cpuid.c | 55 +++++++++++++++++++++++++++++++-------------
1 file changed, 39 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index a16d6e070c11..1064e4d68718 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -61,18 +61,24 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
return ret;
}
-#define F feature_bit
+#define F(name) \
+({ \
+ KVM_VALIDATE_CPU_CAP_USAGE(name); \
+ feature_bit(name); \
+})
/* Scattered Flag - For features that are scattered by cpufeatures.h. */
#define SF(name) \
({ \
BUILD_BUG_ON(X86_FEATURE_##name >= MAX_CPU_FEATURES); \
+ KVM_VALIDATE_CPU_CAP_USAGE(name); \
(boot_cpu_has(X86_FEATURE_##name) ? F(name) : 0); \
})
/* Features that KVM supports only on 64-bit kernels. */
#define X86_64_F(name) \
({ \
+ KVM_VALIDATE_CPU_CAP_USAGE(name); \
(IS_ENABLED(CONFIG_X86_64) ? F(name) : 0); \
})
@@ -95,6 +101,7 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
#define AF(name) \
({ \
BUILD_BUG_ON(__feature_leaf(X86_FEATURE_##name) != CPUID_1_EDX); \
+ BUILD_BUG_ON(kvm_cpu_cap_init_in_progress != CPUID_8000_0001_EDX); \
feature_bit(name); \
})
@@ -622,22 +629,34 @@ static __always_inline u32 raw_cpuid_get(struct cpuid_reg cpuid)
return *__cpuid_entry_get_reg(&entry, cpuid.reg);
}
-static __always_inline void kvm_cpu_cap_init(u32 leaf, u32 mask)
-{
- const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);
+/*
+ * Assert that the feature bit being declared, e.g. via F(), is in the CPUID
+ * word that's being initialized. Exempt 0x8000_0001.EDX usage of 0x1.EDX
+ * features, as AMD duplicated many 0x1.EDX features into 0x8000_0001.EDX.
+ */
+#define KVM_VALIDATE_CPU_CAP_USAGE(name) \
+do { \
+ u32 __leaf = __feature_leaf(X86_FEATURE_##name); \
+ \
+ BUILD_BUG_ON(__leaf != kvm_cpu_cap_init_in_progress); \
+} while (0)
- /*
- * For kernel-defined leafs, mask the boot CPU's pre-populated value.
- * For KVM-defined leafs, explicitly set the leaf, as KVM is the one
- * and only authority.
- */
- if (leaf < NCAPINTS)
- kvm_cpu_caps[leaf] &= mask;
- else
- kvm_cpu_caps[leaf] = mask;
-
- kvm_cpu_caps[leaf] &= raw_cpuid_get(cpuid);
-}
+/*
+ * For kernel-defined leafs, mask the boot CPU's pre-populated value. For KVM-
+ * defined leafs, explicitly set the leaf, as KVM is the one and only authority.
+ */
+#define kvm_cpu_cap_init(leaf, mask) \
+do { \
+ const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32); \
+ const u32 __maybe_unused kvm_cpu_cap_init_in_progress = leaf; \
+ \
+ if (leaf < NCAPINTS) \
+ kvm_cpu_caps[leaf] &= (mask); \
+ else \
+ kvm_cpu_caps[leaf] = (mask); \
+ \
+ kvm_cpu_caps[leaf] &= raw_cpuid_get(cpuid); \
+} while (0)
/*
* Undefine the MSR bit macro to avoid token concatenation issues when
@@ -870,6 +889,10 @@ void kvm_set_cpu_caps(void)
}
EXPORT_SYMBOL_GPL(kvm_set_cpu_caps);
+#undef kvm_cpu_cap_init
+#undef KVM_VALIDATE_CPU_CAP_USAGE
+#define KVM_VALIDATE_CPU_CAP_USAGE(name)
+
struct kvm_cpuid_array {
struct kvm_cpuid_entry2 *entries;
int maxnent;
--
2.45.0.215.g3402c0e53f-goog
