Re: [PATCH 2/5] i386/hvf: Fix for UB in handling CPUID function 0xD

[Roman Bolshakov]

On Tue, Nov 05, 2024 at 04:57:57PM +0100, Phil Dennis-Jordan wrote:
> 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.
> 

Thanks for correcting the regression.

Reviewed-by: Roman Bolshakov <rbolshakov@ddn.com>