RE: [PATCH 1/3] Revert "x86/retpoline: Remove .text..__x86.return_thunk section"

[Kaplan, David]

[AMD Official Use Only - General]

> -----Original Message-----
> From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Sent: Tuesday, October 10, 2023 3:19 PM
> To: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>; Kaplan, David
> <David.Kaplan@xxxxxxx>; x86@xxxxxxxxxx; luto@xxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH 1/3] Revert "x86/retpoline: Remove
> .text..__x86.return_thunk section"
>
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>
> On Tue, Oct 10, 2023 at 10:04:29PM +0200, Borislav Petkov wrote:
> > On Tue, Oct 10, 2023 at 12:57:21PM -0700, Josh Poimboeuf wrote:
> > > Also we could make objtool properly detect the non-relocated jump
> > > target.
> >
> > I was wondering about that... I guess it can compute the JMP target
> > and compare it to the address of __x86_return_thunk?
>
> Fine, you twisted my arm ;-)
>
> This seems to do the trick.  Lemme write up a proper patch.
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c index
> e308d1ba664e..6cbc9812a36e 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -1610,6 +1610,11 @@ static int add_jump_destinations(struct
> objtool_file *file)
>                         return -1;
>                 }
>
> +               if (jump_dest->sym && jump_dest->sym->return_thunk) {
> +                       add_return_call(file, insn, true);
> +                       continue;
> +               }
> +
>                 /*
>                  * Cross-function jump.
>                  */

This looks good to me in my testing so far.

--David Kaplan