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Date: Thu, 4 Apr 2019 10:03:58 -0700
From: Kees Cook <keescook@...omium.org>
To: "Reshetova, Elena" <elena.reshetova@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, Kernel Hardening <kernel-hardening@...ts.openwall.com>, 
	Andy Lutomirski <luto@...capital.net>, Josh Poimboeuf <jpoimboe@...hat.com>, Jann Horn <jannh@...gle.com>, 
	"Perla, Enrico" <enrico.perla@...el.com>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, 
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH] x86/entry/64: randomize kernel stack offset upon syscall

On Thu, Apr 4, 2019 at 4:41 AM Reshetova, Elena
<elena.reshetova@...el.com> wrote:
> What I still don't fully understand here (due to my little knowledge of
> compilers) and afraid of is that the asm code that alloca generates (see my version)
> and the alignment might differ on the different targets, etc.

I guess it's possible, but for x86_64, since appears to be consistent.

> If you tried it on yours, can you send me the asm code that it produced for you?
> Is it different from mine?

You can compare compiler outputs here. Here's gcc vs clang for this code:
https://godbolt.org/z/WJSbN8
You can adjust compiler versions, etc.

-- 
Kees Cook

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