KVM: x86: Add BUILD_BUG_ON() to detect bad usage of "scattered" flags

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Add a compile-time assert in the SF() macro to detect improper usage,
i.e. to detect passing in an X86_FEATURE_* flag that isn't actually
scattered by the kernel.  Upcoming feature flags will be 100% KVM-only
and will have X86_FEATURE_* macros that point at a kvm_only_cpuid_leafs
word, not a kernel-defined word.  Using SF() and thus boot_cpu_has() for
such feature flags would access memory beyond x86_capability[NCAPINTS]
and at best incorrectly hide a feature, and at worst leak kernel state to
userspace.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221125125845.1182922-2-jiaxi.chen@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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Sean Christopherson 2022-11-25 20:58:38 +08:00 • committed by Paolo Bonzini

parent 7927e27549

commit c4690d0161

1 changed files with 7 additions and 1 deletions

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arch/x86/kvm/cpuid.c

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