linux-kernel - Re: 3.14-rc2 XFS backtrace because irqs

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, 15 Feb 2014 14:43:03 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>, Dave Chinner <david@...morbit.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Sandeen <sandeen@...deen.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.

On Sat, Feb 15, 2014 at 2:28 PM, Dave Jones <davej@...hat.com> wrote:
>
> I've got a shitload of debug options enabled, which may explain it.
> Or perhaps that new STACK_PROTECTOR_STRONG stuff ?

Well, a lot of it is just the callee-saved registers. The compiler
will tend to preferentially allocate registers in the callee-trashed
registers, but if the function isn't a leaf function, any registers
that are live around a function call will have to be saved somewhere -
either explicitly around the function call, or - more likely - in
callee-saved registers that then get saved in the prologue/epilogue of
the function. And this will happen even in leaf functions when there
is enough register pressure that the callee-trashed registers aren't
sufficient (which is pretty common).

So saving 5-6 registers on the stack (in addition to any actual stack
frame) is pretty much the norm for anything but the very simplest
cases.

But yeah, I'm sure some config options make it worse.
STACK_PROTECTOR_STRONG could easily be one of those.

            Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/