linux-kernel - Re: objtool warnings in prerelease clang-9

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sat, 6 Jul 2019 10:50:01 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kees Cook <keescook@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Craig Topper <craig.topper@...el.com>,
        Alexander Potapenko <glider@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Stephen Hines <srhines@...gle.com>
Subject: Re: objtool warnings in prerelease clang-9

On Tue, Jul 02, 2019 at 11:58:27PM +0200, Thomas Gleixner wrote:
> platform-quirks.o:
> 
>         if (x86_platform.set_legacy_features)
>   74:   4c 8b 1d 00 00 00 00    mov    0x0(%rip),%r11        # 7b <x86_early_init_platform_quirks+0x7b>
>   7b:   4d 85 db                test   %r11,%r11
>   7e:   0f 85 00 00 00 00       jne    84 <x86_early_init_platform_quirks+0x84>
>                 x86_platform.set_legacy_features();
> }
>   84:   c3                      retq   
> 
> That jne jumps to __x86_indirect_thunk_r11, aka. ratpoutine.
> 
> No idea why objtool thinks that the instruction at 0x84 is not
> reachable. Josh?

That's a conditional tail call, which is something GCC never does.
Objtool doesn't understand that, so we'll need to fix it.

-- 
Josh