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Date: Wed, 3 Nov 2021 09:35:59 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Kees Cook <keescook@chromium.org>, Ard Biesheuvel <ardb@kernel.org>,
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Subject: Re: [PATCH] static_call,x86: Robustify trampoline patching
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On Tue, Nov 02, 2021 at 05:20:05PM -0700, Andy Lutomirski wrote:
> I think that's a big mistake -- any sane ENDBR-using scheme would
> really prefer that ENDBR to be right next to the actual function body,
> and really any scheme would benefit due to better cache locality. 

Agreed, IBT/BTI want the landing pad in front of the actual function.

> But, more importantly, IMO any sane ENDBR-using scheme wants to
> generate the indirect stub as part of code gen for the actual
> function.

Sorta, I really want to be able to not have a landing pad for functions
whose address is never taken. At that point it doesn't matter if it gets
generated along with the function and then stripped/poisoned later, or
generated later.

As such, the landing pad should not be part of the function proper,
direct calls should never observe it.

Less landing pads is more better.