Re: [PATCH qemu-server] query-machine-capabilities: check vendor string length for strncmp

[Fiona Ebner <f.ebner@proxmox.com>]

Am 29.07.26 um 10:41 AM schrieb Kaiyang Wu:
> Gentle ping.
> 
> Kaiyang
> 
> On 2026-07-16 10:31, Kaiyang Wu wrote:
>> Intel TDX and AMD SEV are both x86_64 only extensions [0] [1]. I
>> wonder if the best approach for this issue is to just add a
>> conditional compilation check for x86_64 target architecture.
>>
>> If that works I will switch to compile time architecture check in v2.
>>
>> [0]: https://docs.kernel.org/arch/x86/tdx.html
>> [1]: https://docs.kernel.org/virt/kvm/x86/amd-memory-encryption.html
>>

Yes, I think the checks for AuthenticAMD and GenuineIntel can be put
into conditional compilation for x86_64 right now. There already is a
conditional inside query_cpu_capabilities_sev() but that can be dropped
afterwards.

>> On 2026-07-13 22:15, Fabian Grünbichler wrote:
>>> On June 3, 2026 7:50 am, Kaiyang Wu wrote:
>>>> Fix build error on unknown vendors ('fallback'):
>>>>
>>>>     error: ‘strncmp’ of strings of length 7 and 12 and bound of 12
>>>> evaluates to nonzero [-Werror=string-compare]
>>>>
>>>> Signed-off-by: Kaiyang Wu <wukaiyang@loongfans.cn>
>>>> ---
>>>>   src/query-machine-capabilities/query-machine-capabilities.c | 4 ++--
>>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/src/query-machine-capabilities/query-machine-
>>>> capabilities.c b/src/query-machine-capabilities/query-machine-
>>>> capabilities.c
>>>> index abb47acd..25d06db7 100644
>>>> --- a/src/query-machine-capabilities/query-machine-capabilities.c
>>>> +++ b/src/query-machine-capabilities/query-machine-capabilities.c
>>>> @@ -204,7 +204,7 @@ int main() {
>>>>           eprintf("Error writing to file '" OUTPUT_PATH "': %s\n",
>>>> strerror(errno));
>>>>       }
>>>> -    if (strncmp(vendor, "AuthenticAMD", 12) == 0) {
>>>> +    if (strncmp(vendor, "AuthenticAMD", strnlen(vendor, 12)) == 0) {
>>>
>>> this is wrong - if the vendor is "Authentic" the code would now think
>>> it's AMD.. the same would be true if vendor is "AuthenticAMDsomething",
>>> because it would only look at the first 12 bytes (granted, that is a
>>> pre-existing issue ;)).
>>>
>>> instead, we'd first need to check for the length, and if it is 12, do
>>> the existing checks, if not, either add checks for other vendors, or
>>> reject/abort..
>>>
>>>>           cpu_caps_amd_sev_t caps_sev;
>>>>           query_cpu_capabilities_sev(&caps_sev);
>>>> @@ -222,7 +222,7 @@ int main() {
>>>>               caps_sev.sev_es_support ? "true" : "false",
>>>>               caps_sev.sev_snp_support ? "true" : "false"
>>>>           );
>>>> -    } else if (strncmp(vendor, "GenuineIntel", 12) == 0) {
>>>> +    } else if (strncmp(vendor, "GenuineIntel", strnlen(vendor, 12))
>>>> == 0) {
>>>
>>> same applies here, but with `Genuine` (or any other substring prefix of
>>> `GenuineIntel`)..
>>>
>>>>           cpu_caps_intel_tdx_t caps_tdx;
>>>>           if (query_cpu_capabilities_tdx(&caps_tdx) == 0) {
>>>>               ret = fprintf(file,
>>>> -- 
>>>> 2.52.0
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>
> 
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