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@xxxxxxxxxx>
---
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;
break;
case 1:
- entry->ecx = F(MOVBE);
- ++array->nent;
+ entry.ecx = F(MOVBE);
break;
case 7:
- 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);
break;
+ 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@xxxxxxxxxx>
+ if (array->nent >= array->maxnent)
+ return -E2BIG;
+
+ entry.function = func;
+ memcpy(&array->entries[array->nent++], &entry, sizeof(entry));
+
+out:
return 0;
}
--
2.30.2
