linux-kernel - Re: [PATCH] crypto: x86/aes - Don't use %rbp as temporary register

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Date:   Thu, 18 May 2017 19:50:17 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-crypto@...r.kernel.org,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] crypto: x86/aes - Don't use %rbp as temporary register

On Thu, May 18, 2017 at 08:56:32PM -0500, Josh Poimboeuf wrote:
> > 
> > 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?
> 
> This warning was only recently added, with the goal of flushing out
> these types of issues with hand-coded asm to make frame pointer based
> stack traces more reliable.  I can take a look at fixing the rest of
> them if you want.
> 

Okay.  I'm worried you might run into one that is difficult to fix due to lack
of spare registers.  But if you're interested in looking into it, please go
ahead.  Thanks!

Eric