From: Andrew Lutomirski <luto@mit.edu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>,
richard -rw- weinberger <richard.weinberger@gmail.com>,
Adrian Bunk <bunk@stusta.de>,
"H. Peter Anvin" <hpa@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] fixing the UML failure root cause
Date: Thu, 13 Oct 2011 23:30:00 -0700 [thread overview]
Message-ID: <CAObL_7ED+qwOgSH+WsLXvZqC83MX1Q-_1NtcgH-cPe9ghLveZg@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzoDi-WP-2Uq-33FAGfMPZbrsvg6_QWEKm1zczET539PQ@mail.gmail.com>
On Thu, Oct 13, 2011 at 9:46 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Oct 13, 2011 at 8:40 PM, Andrew Lutomirski <luto@mit.edu> wrote:
>>
>> How does that work? The tricky case is when one of those three words
>> spans a page boundary if the access to the first page is valid, but
>> the access to the second page is not. When that happens, if we report
>> the fault as coming from the first page, then UML is likely to get
>> think the fault was spurious and enter an infinite loop.
>
> Hmm. Gaah, I just find that memcpy loop disgusting.
>
Yeah, it's not pretty.
> We already have that ugly "uaccess_error" crap in handle_exception(),
> we might as well do something like the attached and just say "hey, now
> you can catch the page fault information for a get_user/put_user
> fault".
>
> Isn't that much nicer?
I actually tried this. To really get it right, though, I also need to
either hook the access_ok failure paths (either every single one or
just the ones that matter for those three syscalls, which could be
fragile) or to check access_ok separately in the vsyscall emulation
code. This also takes up 16 bytes of stack just to support a corner
case of a legacy code path.
Another idea is to have a flag that asks the fault handlers to call
force_sig_info for us. That's just one bit of per-thread state. Then
the vsyscall emulation code could check access_ok, force a signal if
access is not ok, then set the flag and do the syscall. And maybe
some processes would want to opt in to that mode anyway -- arguably
EFAULT is a serious programmer error and should be dealt with more
harshly than other syscall misuses.
Admittedly, UML probably doesn't care about recovering vgettimeofday
pointed at kernel space...
--Andy
next prev parent reply other threads:[~2011-10-14 6:30 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-03 9:08 [3.1 patch] x86: default to vsyscall=native Adrian Bunk
2011-10-03 13:04 ` Andrew Lutomirski
2011-10-03 17:33 ` Adrian Bunk
2011-10-03 18:06 ` Andrew Lutomirski
2011-10-03 18:41 ` Adrian Bunk
2011-10-05 22:13 ` Andrew Lutomirski
2011-10-05 22:22 ` richard -rw- weinberger
2011-10-05 22:30 ` Adrian Bunk
2011-10-05 22:41 ` richard -rw- weinberger
2011-10-05 22:46 ` Andrew Lutomirski
2011-10-05 23:36 ` Andrew Lutomirski
2011-10-06 3:06 ` Andrew Lutomirski
2011-10-06 12:12 ` richard -rw- weinberger
2011-10-06 15:37 ` richard -rw- weinberger
2011-10-06 18:16 ` Andrew Lutomirski
2011-10-06 18:34 ` Linus Torvalds
2011-10-07 0:48 ` Andrew Lutomirski
2011-10-10 11:19 ` richard -rw- weinberger
2011-10-10 11:48 ` Ingo Molnar
2011-10-10 15:31 ` Andrew Lutomirski
2011-10-11 6:22 ` Ingo Molnar
2011-10-11 17:24 ` [RFC] fixing the UML failure root cause Andrew Lutomirski
2011-10-13 6:19 ` Linus Torvalds
2011-10-13 8:40 ` Andrew Lutomirski
2011-10-14 4:46 ` Linus Torvalds
2011-10-14 6:30 ` Andrew Lutomirski [this message]
2011-10-14 20:10 ` Linus Torvalds
2011-10-21 21:01 ` [PATCH] x86-64: Set siginfo and context on vsyscall emulation faults Andy Lutomirski
2011-10-22 4:46 ` Linus Torvalds
2011-10-22 9:07 ` Andy Lutomirski
2011-11-08 0:33 ` [PATCH 0/2] Fix and re-enable vsyscall=emulate Andy Lutomirski
2011-11-08 0:33 ` [PATCH 1/2] x86-64: Set siginfo and context on vsyscall emulation faults Andy Lutomirski
2011-12-05 13:23 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2011-11-08 0:33 ` [PATCH 2/2] x86: Default to vsyscall=emulate Andy Lutomirski
2011-12-05 13:24 ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2011-12-02 22:47 ` [PATCH 0/2] Fix and re-enable vsyscall=emulate Andy Lutomirski
2011-12-05 11:18 ` H. Peter Anvin
2011-10-14 19:53 ` [RFC] fixing the UML failure root cause richard -rw- weinberger
2011-10-14 20:17 ` Andrew Lutomirski
2011-10-14 20:23 ` richard -rw- weinberger
2011-10-14 20:31 ` Andrew Lutomirski
2011-10-14 20:39 ` richard -rw- weinberger
2011-10-14 22:28 ` richard -rw- weinberger
2011-10-15 16:57 ` Ingo Molnar
2011-10-05 22:24 ` [3.1 patch] x86: default to vsyscall=native Adrian Bunk
2011-10-03 13:19 ` richard -rw- weinberger
2011-10-03 17:46 ` Adrian Bunk
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=CAObL_7ED+qwOgSH+WsLXvZqC83MX1Q-_1NtcgH-cPe9ghLveZg@mail.gmail.com \
--to=luto@mit.edu \
--cc=bunk@stusta.de \
--cc=hpa@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=mingo@redhat.com \
--cc=richard.weinberger@gmail.com \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=x86@kernel.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).