LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andy Lutomirski <luto@amacapital.net>
To: "H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <andi@firstfloor.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>
Subject: [PATCH 0/2] x86_64,signal: Fix the set of saved segment registers
Date: Fri, 11 Jul 2014 09:29:21 -0700	[thread overview]
Message-ID: <cover.1405095200.git.luto@amacapital.net> (raw)

The x86_64 signal code claims to save and restore CS, FS, and GS,
and it further claims that this is the minimal set that's needed.

Neither of these claims is true.  The code does not, and AFAICT
never has, saved or restored FS and GS, nor does it need to.  On the
other hand, all 64-bit syscalls (and rt_sigreturn in particular)
clobber SS, making it impossible for signal handlers to correctly
restore SS without using a trampoline or ptracing themselves.

This patchset saves and restores SS in the __pad0 slot and renames
the FS and GS slots __pad1 and __pad2 to more accurately document
their purpose.

I discovered this while writing a test for espfix64.

Andy Lutomirski (2):
  x86_64,signal: Save and restore SS in signal frames
  x86_64,signal: Remove 'fs' and 'gs' from sigcontext

 arch/x86/include/asm/sigcontext.h      |  6 +++---
 arch/x86/include/uapi/asm/sigcontext.h |  6 +++---
 arch/x86/kernel/signal.c               | 12 +++---------
 3 files changed, 9 insertions(+), 15 deletions(-)

-- 
1.9.3


             reply	other threads:[~2014-07-11 16:29 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-11 16:29 Andy Lutomirski [this message]
2014-07-11 16:29 ` [PATCH 1/2] x86_64,signal: Save and restore SS in signal frames Andy Lutomirski
2015-03-09 20:15   ` Andy Lutomirski
2014-07-11 16:29 ` [PATCH 2/2] x86_64,signal: Remove 'fs' and 'gs' from sigcontext Andy Lutomirski
2014-07-11 18:12   ` Andi Kleen
2014-07-11 18:39     ` Andy Lutomirski
2014-07-12  2:09       ` H. Peter Anvin
2014-07-12  2:04   ` H. Peter Anvin
2014-07-12  2:21   ` Linus Torvalds
2014-07-12  2:26     ` H. Peter Anvin
2014-07-12  8:39     ` Andy Lutomirski
2014-07-12 18:37       ` Andi Kleen
2014-07-12 18:40         ` H. Peter Anvin
2014-07-12 18:52           ` Andi Kleen
2014-07-12 21:17             ` Andy Lutomirski
2014-07-18  1:13               ` Andy Lutomirski

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=cover.1405095200.git.luto@amacapital.net \
    --to=luto@amacapital.net \
    --cc=andi@firstfloor.org \
    --cc=hpa@zytor.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=viro@ZenIV.linux.org.uk \
    --cc=x86@kernel.org \
    --subject='Re: [PATCH 0/2] x86_64,signal: Fix the set of saved segment registers' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).