Emanuele Giuseppe Esposito <eesposit@xxxxxxxxxx> writes:
> 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.
>
> 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..27059ddf9f0a 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));
> + entry.function = func;
>
> 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.eax = 0;
Nitpick: there's no need to set entry.eax = 0 as the whole structure was
zeroed. Also, '|=' for flags could be just '='.
> + entry.ecx = F(RDPID);
> break;
> + default:
> + goto out;
> }
>
> + if (array->nent >= array->maxnent)
> + return -E2BIG;
> +
> + memcpy(&array->entries[array->nent++], &entry, sizeof(entry));
> +
> +out:
> return 0;
> }
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
--
Vitaly
