lkml.org 
[lkml]   [2017]   [May]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] crypto: x86/aes - Don't use %rbp as temporary register
On Wed, May 17, 2017 at 03:44:27PM -0500, Josh Poimboeuf wrote:
> On Tue, May 16, 2017 at 09:03:08PM -0700, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> >
> > When using the "aes-asm" implementation of AES (*not* the AES-NI
> > implementation) on an x86_64, v4.12-rc1 kernel with lockdep enabled, the
> > following warning was reported, along with a long unwinder dump:
> >
> > WARNING: kernel stack regs at ffffc90000643558 in kworker/u4:2:155 has bad 'bp' value 000000000000001c
> >
> > The problem is that aes_enc_block() and aes_dec_block() use %rbp as a
> > temporary register, which breaks stack traces if an interrupt occurs.
> >
> > Fix this by replacing %rbp with %r9, which was being used to hold the
> > saved value of %rbp. This required rearranging the AES round macro
> > slightly since %r9d cannot be used as the target of a move from %ah-%dh.
> >
> > Performance is essentially unchanged --- actually about 0.2% faster than
> > before. Interestingly, I also measured aes-generic as being nearly 7%
> > faster than aes-asm, so perhaps aes-asm has outlived its usefulness...
> >
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
>
> Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
>

Hmm, it looks like a number of other algorithms in arch/x86/crypto/ use %rbp (or
%ebp), e.g. blowfish, camellia, cast5, and aes-i586. Presumably they have the
same problem. I'm a little confused: do these all need to be fixed, and
when/why did this start being considered broken?

Eric

\
 
 \ /
  Last update: 2017-05-18 00:22    [W:0.069 / U:0.452 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site