From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Herbert Xu <herbert@gondor.apana.org.au>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andy Lutomirski <luto@kernel.org>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: Re: x86-64: Maintain 16-byte stack alignment
Date: Thu, 12 Jan 2017 14:15:11 -0600 [thread overview]
Message-ID: <20170112201511.yj5ekqmj76r2yv6t@treble> (raw)
In-Reply-To: <CALCETrVz-wEFVUwrpS8-Ln9SWnsF5KxkqJC-Br6wJ+e0LGM9UA@mail.gmail.com>
On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote:
> On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> >>
> >> Just to clarify, I think you're asking if, for versions of gcc which
> >> don't support -mpreferred-stack-boundary=3, objtool can analyze all C
> >> functions to ensure their stacks are 16-byte aligned.
> >>
> >> It's certainly possible, but I don't see how that solves the problem.
> >> The stack will still be misaligned by entry code. Or am I missing
> >> something?
> >
> > I think the argument is that we *could* try to align things, if we
> > just had some tool that actually then verified that we aren't missing
> > anything.
> >
> > I'm not entirely happy with checking the generated code, though,
> > because as Ingo says, you have a 50:50 chance of just getting it right
> > by mistake. So I'd much rather have some static tool that checks
> > things at a code level (ie coccinelle or sparse).
>
> What I meant was checking the entry code to see if it aligns stack
> frames, and good luck getting sparse to do that. Hmm, getting 16-byte
> alignment for real may actually be entirely a lost cause. After all,
> I think we have some inline functions that do asm volatile ("call
> ..."), and I don't see any credible way of forcing alignment short of
> generating an entirely new stack frame and aligning that.
Actually we already found all such cases and fixed them by forcing a new
stack frame, thanks to objtool. For example, see 55a76b59b5fe.
> Ick. This
> whole situation stinks, and I wish that the gcc developers had been
> less daft here in the first place or that we'd noticed and gotten it
> fixed much longer ago.
>
> Can we come up with a macro like STACK_ALIGN_16 that turns into
> __aligned__(32) on bad gcc versions and combine that with your sparse
> patch?
--
Josh
next prev parent reply other threads:[~2017-01-12 20:15 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-10 14:33 x86-64: Maintain 16-byte stack alignment Herbert Xu
2017-01-10 14:39 ` Herbert Xu
2017-01-10 17:05 ` Linus Torvalds
2017-01-10 17:09 ` Andy Lutomirski
2017-01-11 3:11 ` Herbert Xu
2017-01-11 3:30 ` Linus Torvalds
2017-01-11 4:17 ` Linus Torvalds
2017-01-11 4:35 ` Herbert Xu
2017-01-11 6:01 ` Andy Lutomirski
2017-01-12 6:21 ` Andy Lutomirski
2017-01-12 7:40 ` Ingo Molnar
2017-01-12 14:02 ` Josh Poimboeuf
2017-01-12 19:51 ` Linus Torvalds
2017-01-12 20:08 ` Andy Lutomirski
2017-01-12 20:15 ` Josh Poimboeuf [this message]
2017-01-12 20:55 ` Josh Poimboeuf
2017-01-12 21:40 ` Linus Torvalds
2017-01-13 8:38 ` Herbert Xu
2017-01-13 1:46 ` Andy Lutomirski
2017-01-13 3:11 ` Josh Poimboeuf
2017-01-13 3:23 ` Andy Lutomirski
2017-01-13 4:27 ` Josh Poimboeuf
[not found] ` <CA+55aFzRrSwGxxfZk-RUEnsz=xhcSmOwE1CenfCPBWtsS9MwDw@mail.gmail.com>
2017-01-13 5:07 ` Josh Poimboeuf
2017-01-13 8:43 ` Herbert Xu
2017-01-13 8:42 ` Herbert Xu
2017-01-13 8:39 ` Herbert Xu
2017-01-13 8:36 ` Herbert Xu
2017-01-13 13:07 ` Josh Poimboeuf
[not found] ` <CA+55aFw+Z_ieo6DzTVB6_-TvQ0jj60s=T0mvXfqkBVFdKFPw_Q@mail.gmail.com>
2017-01-11 8:06 ` Ard Biesheuvel
2017-01-11 8:09 ` Herbert Xu
2017-01-11 18:20 ` Andy Lutomirski
2017-01-12 7:05 ` Herbert Xu
2017-01-12 7:46 ` Ingo Molnar
2017-01-12 14:49 ` Josh Poimboeuf
2017-01-12 7:51 ` Andy Lutomirski
2017-01-12 8:04 ` Herbert Xu
2017-01-12 8:18 ` Ingo Molnar
2017-01-12 15:03 ` Josh Poimboeuf
2017-01-12 15:06 ` Herbert Xu
2017-01-12 15:18 ` Josh Poimboeuf
2017-01-12 15:10 ` Josh Poimboeuf
2017-01-10 17:30 ` Ard Biesheuvel
2017-01-10 19:00 ` Andy Lutomirski
2017-01-10 19:16 ` Ard Biesheuvel
2017-01-10 19:22 ` Andy Lutomirski
2017-01-10 20:00 ` Ard Biesheuvel
2017-01-10 23:25 ` Andy Lutomirski
2017-01-11 3:26 ` Herbert Xu
2017-01-11 3:26 ` Herbert Xu
2017-01-11 3:16 ` Herbert Xu
2017-01-11 3:15 ` Herbert Xu
2017-01-12 6:12 ` Herbert Xu
2017-01-12 8:01 ` Ard Biesheuvel
2017-01-12 8:06 ` Herbert Xu
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