On Fri, Aug 07, 2026, Gokul K wrote:
> compare_xsave() stops at index 4094, so the last byte of the XSAVE state
> is never compared. Both buffers handed to it are 4096 bytes: the host
> copy is a struct kvm_xsave, whose region[] member is 1024 u32s, and the
> guest copy is the PAGE_SIZE shared page that guest_code_xsave() runs
> XSAVE into. A VMSA synchronization bug that corrupted only that final
> byte would go unreported and the test would still pass.
>
> Bound the loop with sizeof(struct kvm_xsave) rather than an open-coded
> length, and make the index unsigned so it does not mix signedness with
> sizeof.
>
> Fixes: 8c53183dbaa2 ("selftests: kvm: add test for transferring FPU state
> into VMSA")
> Signed-off-by: Gokul K <[email protected]>
> ---
> tools/testing/selftests/kvm/x86/sev_smoke_test.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/x86/sev_smoke_test.c
> b/tools/testing/selftests/kvm/x86/sev_smoke_test.c
> index 6b2cbe2a90b7..c7af27954356 100644
> --- a/tools/testing/selftests/kvm/x86/sev_smoke_test.c
> +++ b/tools/testing/selftests/kvm/x86/sev_smoke_test.c
> @@ -90,9 +90,10 @@ asm("guest_code_xsave:\n"
>
> static void compare_xsave(u8 *from_host, u8 *from_guest)
> {
> - int i;
> + unsigned int i;
> bool bad = false;
> - for (i = 0; i < 4095; i++) {
The fix looks right, but this is so bizarrely wrong that I can't help but wonder
if it was somehow intentional.
Paolo?
> +
> + for (i = 0; i < sizeof(struct kvm_xsave); i++) {
> if (from_host[i] != from_guest[i]) {
> printf("mismatch at %u | %02hhx %02hhx\n",
> i, from_host[i], from_guest[i]);
> --
> 2.54.0
>
>
