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

[Kaiyang Wu]

Thanks, v2 addressed this using conditional compilation.

On 2026-07-29 18:16, Fiona Ebner wrote:

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 <wukaiy...@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