On 08/04/2021 22:29, Sean Christopherson wrote:
On Thu, Apr 08, 2021, Emanuele Giuseppe Esposito wrote:
When retrieving emulated CPUID entries, check for an insufficient array size if and only if KVM is actually inserting an entry. If userspace has a priori knowledge of the exact array size, KVM_GET_EMULATED_CPUID will incorrectly fail due to effectively requiring an extra, unused entry.
Fixes: 433f4ba19041 ("KVM: x86: fix out-of-bounds write in KVM_GET_EMULATED_CPUID (CVE-2019-19332)") Signed-off-by: Emanuele Giuseppe Esposito eesposit@redhat.com
arch/x86/kvm/cpuid.c | 33 ++++++++++++++++----------------- 1 file changed, 16 insertions(+), 17 deletions(-)
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 6bd2f8b830e4..d30194081892 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -567,34 +567,33 @@ static struct kvm_cpuid_entry2 *do_host_cpuid(struct kvm_cpuid_array *array, static int __do_cpuid_func_emulated(struct kvm_cpuid_array *array, u32 func) {
- struct kvm_cpuid_entry2 *entry;
- if (array->nent >= array->maxnent)
return -E2BIG;
- struct kvm_cpuid_entry2 entry;
- entry = &array->entries[array->nent];
- entry->function = func;
- entry->index = 0;
- entry->flags = 0;
- memset(&entry, 0, sizeof(entry));
switch (func) { case 0:
entry->eax = 7;++array->nent;
entry.eax = 7;
entry->ecx = F(MOVBE);++array->nent;
entry.ecx = F(MOVBE);
entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;entry->eax = 0;entry->ecx = F(RDPID);++array->nent;- default:
entry.flags = KVM_CPUID_FLAG_SIGNIFCANT_INDEX;entry.ecx = F(RDPID);- default:
goto out;
- /* This check is performed only when func is valid */
Sorry to keep nitpicking and bikeshedding.
No problem at all. Any comment is very welcome :)
Funcs aren't really "invalid", KVM
just doesn't have any features it emulates in other leafs. Maybe be more literal in describing what triggers the check?
/* Check the array capacity iff the entry is being copied over. */
What I mean here is that a func is "valid" if it matches one of the cases of the switch statement. If it is not valid, it ends up in the default case. But I agree, will change the comment your suggestion and resend.
Thank you, Emanuele
Not a sticking point, so either way:
Reviewed-by: Sean Christopherson seanjc@google.com
- if (array->nent >= array->maxnent)
return -E2BIG;- entry.function = func;
- memcpy(&array->entries[array->nent++], &entry, sizeof(entry));
+out: return 0; } -- 2.30.2