diff options
| author | Sean Christopherson <seanjc@google.com> | 2021-09-29 15:24:26 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-09-30 04:27:08 -0400 |
| commit | 25b9784586a41f1fccc4d2cf7f210252b9df149c (patch) | |
| tree | 3d84be6282e401d3c028bdc88080dcc2ba949904 | |
| parent | 62dd57dd67d74ff5bfdfc28260a35cc4a31babb3 (diff) | |
KVM: x86: Manually retrieve CPUID.0x1 when getting FMS for RESET/INIT
Manually look for a CPUID.0x1 entry instead of bouncing through
kvm_cpuid() when retrieving the Family-Model-Stepping information for
vCPU RESET/INIT. This fixes a potential undefined behavior bug due to
kvm_cpuid() using the uninitialized "dummy" param as the ECX _input_,
a.k.a. the index.
A more minimal fix would be to simply zero "dummy", but the extra work in
kvm_cpuid() is wasteful, and KVM should be treating the FMS retrieval as
an out-of-band access, e.g. same as how KVM computes guest.MAXPHYADDR.
Both Intel's SDM and AMD's APM describe the RDX value at RESET/INIT as
holding the CPU's FMS information, not as holding CPUID.0x1.EAX. KVM's
usage of CPUID entries to get FMS is simply a pragmatic approach to avoid
having yet another way for userspace to provide inconsistent data.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20210929222426.1855730-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
| -rw-r--r-- | arch/x86/kvm/x86.c | 12 |
1 files changed, 5 insertions, 7 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 833300fc78e3..25bfc12c0d08 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10779,9 +10779,9 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu) void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) { + struct kvm_cpuid_entry2 *cpuid_0x1; unsigned long old_cr0 = kvm_read_cr0(vcpu); unsigned long new_cr0; - u32 eax, dummy; /* * Several of the "set" flows, e.g. ->set_cr0(), read other registers @@ -10862,13 +10862,11 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) * Fall back to KVM's default Family/Model/Stepping of 0x600 (P6/Athlon) * if no CPUID match is found. Note, it's impossible to get a match at * RESET since KVM emulates RESET before exposing the vCPU to userspace, - * i.e. it'simpossible for kvm_cpuid() to find a valid entry on RESET. - * But, go through the motions in case that's ever remedied. + * i.e. it's impossible for kvm_find_cpuid_entry() to find a valid entry + * on RESET. But, go through the motions in case that's ever remedied. */ - eax = 1; - if (!kvm_cpuid(vcpu, &eax, &dummy, &dummy, &dummy, true)) - eax = 0x600; - kvm_rdx_write(vcpu, eax); + cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0); + kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600); vcpu->arch.ia32_xss = 0; |