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

Pawan Gupta
2023-10-23T19:13:41Z

On Mon, Oct 23, 2023 at 11:22:11AM -0700, Josh Poimboeuf wrote:
> On Fri, Oct 20, 2023 at 01:45:03PM -0700, Pawan Gupta wrote:
> > + /* Mitigate CPU data sampling attacks .e.g. MDS */
> > + USER_CLEAR_CPU_BUFFERS
> > +
> > jmp .Lnative_iret
> >
> >
> > @@ -774,6 +780,9 @@ native_irq_return_ldt:
> > */
> > popq %rax /* Restore user RAX */
> >
> > + /* Mitigate CPU data sampling attacks .e.g. MDS */
> > + USER_CLEAR_CPU_BUFFERS
> > +
>
> I'm thinking the comments add unnecessary noise here. The macro name is
> self-documenting enough.
>
> The detail about what mitigations are being done can go above the macro
> definition itself, which the reader can refer to if they want more
> detail about what the macro is doing and why.

Sure, I will move the comments to definition.

> Speaking of the macro name, I think just "CLEAR_CPU_BUFFERS" is
> sufficient. The "USER_" prefix makes it harder to read IMO.

Ok, will drop "USER_".