linux-kernel - Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent

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:   Thu, 14 Sep 2017 10:16:08 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more
 clear and consistent

On Thu, Sep 14, 2017 at 7:48 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> As it turns out, the real problem with this option is that it imposes a
> penalty for CONFIG_FRAME_POINTER=n: even with frame pointers disabled,
> it forces the frame pointer to be saved for each function which uses the
> inline asm "call" statements.  Our current solution doesn't do that.

But couldn't we make the whole stack pointer clobber be dependent on
CONFIG_FRAME_POINTER?

The only reason we do it is to make sure the frame pointer is set up
before the inline asm is emitted, but with frame pointers disabled we
don't need to.

Or was there some other compiler issue?

But yes, talking to the compiler people is a good idea anyway. Both
the clang ones (marking rsp as an in/out register *really* shouldn't
cause them to generate wrong code) and the gcc people (to see if there
are other alternatives).

                      Linus