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SubjectRe: [PATCH] KVM: x86: Fix BUILD_BUG() in __cpuid_entry_get_reg() w/ CONFIG_UBSAN=y
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On 3/25/20 12:12 PM, Sean Christopherson wrote:
> Take the target reg in __cpuid_entry_get_reg() instead of a pointer to a
> struct cpuid_reg. When building with -fsanitize=alignment (enabled by
> CONFIG_UBSAN=y), some versions of gcc get tripped up on the pointer and
> trigger the BUILD_BUG().
>
> Reported-by: Randy Dunlap <rdunlap@infradead.org>
> Fixes: d8577a4c238f8 ("KVM: x86: Do host CPUID at load time to mask KVM cpu caps")
> Fixes: 4c61534aaae2a ("KVM: x86: Introduce cpuid_entry_{get,has}() accessors")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>

LGTM. Thanks.

Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested

> ---
> arch/x86/kvm/cpuid.c | 2 +-
> arch/x86/kvm/cpuid.h | 8 ++++----
> 2 files changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 08280d8a2ac9..16d3ae432420 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -269,7 +269,7 @@ static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
> cpuid_count(cpuid.function, cpuid.index,
> &entry.eax, &entry.ebx, &entry.ecx, &entry.edx);
>
> - kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, &cpuid);
> + kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, cpuid.reg);
> }
>
> void kvm_set_cpu_caps(void)
> diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
> index 23b4cd1ad986..63a70f6a3df3 100644
> --- a/arch/x86/kvm/cpuid.h
> +++ b/arch/x86/kvm/cpuid.h
> @@ -99,9 +99,9 @@ static __always_inline struct cpuid_reg x86_feature_cpuid(unsigned int x86_featu
> }
>
> static __always_inline u32 *__cpuid_entry_get_reg(struct kvm_cpuid_entry2 *entry,
> - const struct cpuid_reg *cpuid)
> + u32 reg)
> {
> - switch (cpuid->reg) {
> + switch (reg) {
> case CPUID_EAX:
> return &entry->eax;
> case CPUID_EBX:
> @@ -121,7 +121,7 @@ static __always_inline u32 *cpuid_entry_get_reg(struct kvm_cpuid_entry2 *entry,
> {
> const struct cpuid_reg cpuid = x86_feature_cpuid(x86_feature);
>
> - return __cpuid_entry_get_reg(entry, &cpuid);
> + return __cpuid_entry_get_reg(entry, cpuid.reg);
> }
>
> static __always_inline u32 cpuid_entry_get(struct kvm_cpuid_entry2 *entry,
> @@ -189,7 +189,7 @@ static __always_inline u32 *guest_cpuid_get_register(struct kvm_vcpu *vcpu,
> if (!entry)
> return NULL;
>
> - return __cpuid_entry_get_reg(entry, &cpuid);
> + return __cpuid_entry_get_reg(entry, cpuid.reg);
> }
>
> static __always_inline bool guest_cpuid_has(struct kvm_vcpu *vcpu,
>


--
~Randy

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