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

[Kaiyang Wu <wukaiyang2003@gmail.com>]

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
> 
> 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
>>>
>>>
>>>
>>>
>>>
>>
>