Re: [PATCH v5] x86/entry_32: Use stack segment selector for VERW operand

[Dave Hansen]

On 7/11/24 15:03, Pawan Gupta wrote:
> +/*
> + * Safer version of CLEAR_CPU_BUFFERS that uses %ss to reference VERW operand
> + * mds_verw_sel. This ensures VERW will not #GP for an arbitrary user %ds.
> + */
> +.macro CLEAR_CPU_BUFFERS_SAFE
> +	ALTERNATIVE "", __stringify(verw %ss:_ASM_RIP(mds_verw_sel)), X86_FEATURE_CLEAR_CPU_BUF
> +.endm

One other thing...

Instead of making a "_SAFE" variant, let's just make the 32-bit version
always safe.

Also, is there any downside to using %ss: on 64-bit?  If not, let's just
update the one and only CLEAR_CPU_BUFFERS use %ss:.