Re: [PATCH v3 2/6] x86/entry_64: Add VERW just before userspace transition

[Pawan Gupta]

On Thu, Oct 26, 2023 at 07:25:27PM +0300, Nikolay Borisov wrote:
> 
> 
> On 25.10.23 г. 23:52 ч., Pawan Gupta wrote:
> 
> <snip>
> 
> > @@ -1520,6 +1530,7 @@ SYM_CODE_START(ignore_sysret)
> >   	UNWIND_HINT_END_OF_STACK
> >   	ENDBR
> >   	mov	$-ENOSYS, %eax
> > +	CLEAR_CPU_BUFFERS
> 
> nit: Just out of curiosity is it really needed in this case or it's doesn
> for the sake of uniformity so that all ring3 transitions are indeed
> covered??

Interrupts returning to kernel don't clear the CPU buffers. I believe
interrupts will be enabled here, and getting an interrupt here could
leak the data that interrupt touched.