i386/hvf: Fix for UB in handling CPUID function 0xD

The handling for CPUID function 0xD (supported XSAVE features) was
improved in a recent patch. Unfortunately, this appears to have
introduced undefined behaviour for cases where ecx > 30, as the result
of (1 << idx) is undefined if idx > 30.

Per Intel SDM section 13.2, the behaviour for ecx values up to and
including 62 are specified. This change therefore specifically sets
all registers returned by the CPUID instruction to 0 for 63 and higher.
Furthermore, the bit shift uses uint64_t, where behaviour for the entire
range of 2..62 is safe and correct.

Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
Link: https://lore.kernel.org/r/20241105155800.5461-3-phil@philjordan.eu
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/hvf/x86_cpuid.c b/target/i386/hvf/x86_cpuid.c
index 3f16b0f363d5b8056e109a452d8d4cbcf7571f42..af9ee17a111d6d1dfd02dae38d2917b0d8b54584 100644 (file)
--- a/target/i386/hvf/x86_cpuid.c
+++ b/target/i386/hvf/x86_cpuid.c
@@ -119,8 +119,8 @@ uint32_t hvf_get_supported_cpuid(uint32_t func, uint32_t idx,
         eax = 0;
         break;
     case 0xD:
-        if (!supported_xcr0 ||
-            (idx > 1 && !(supported_xcr0 & (1 << idx)))) {
+        if (!supported_xcr0 || idx >= 63 ||
+            (idx > 1 && !(supported_xcr0 & (UINT64_C(1) << idx)))) {
             eax = ebx = ecx = edx = 0;
             break;
         }