linux-hardening - Re: [PATCH] x86: Allow for exclusions in checking RETHUNK

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Message-ID: <20220714185006.6brfnnzhz7p7zw3u@treble>
Date:   Thu, 14 Jul 2022 11:50:06 -0700
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel test robot <oliver.sang@...el.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] x86: Allow for exclusions in checking RETHUNK

On Thu, Jul 14, 2022 at 09:18:12AM +0200, Peter Zijlstra wrote:
> On Wed, Jul 13, 2022 at 04:55:56PM -0700, Josh Poimboeuf wrote:
> > Here's the ANNOTATE_UNSAFE_RET idea.
> 
> Right, I suppose that strictly speaking the compiler can do whatever and
> there's no actual guarantee the annotation hits the RET instruction, in
> practise it should work, esp. since noinstr.

Hm, KASAN is introducing a weird function, resulting in a naked return
warning since we have RETHUNK_CFLAGS removed on that file.

0000000000000000 <_sub_I_00099_0>:
   0:	e8 00 00 00 00       	call   5 <_sub_I_00099_0+0x5>	1: R_X86_64_PLT32	__tsan_init-0x4
   5:	c3                   	ret    


Looks like the "KASAN_SANITIZE_rodata.o := n" isn't working somehow?

-- 
Josh