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

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