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 01:40:16 -0700 [thread overview]
Message-ID: <CAObL_7HYnDVUyLA=FQ-qmuh=J=H=JOQTBMP_wt_zwzOfe9-7Hg@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFyMXgzywjXCtS1a5F-BDu_XP4ecg3Tw7zLuawZs0QNYaw@mail.gmail.com>
On Wed, Oct 12, 2011 at 11:19 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Oct 12, 2011 at 5:24 AM, Andrew Lutomirski <luto@mit.edu> wrote:
>>
>> So here's a different approach. It's not perfect: it always blames
>> SEGV_MAPERR instead of SEGV_ACCERR. I implemented it for vgettimeofday
>> but not the other two vsyscalls.
>>
>> What do you think of this approach? If it seems good, I'll finish the
>> patch and submit it.
>
> I think the approach is valid, but you should *not* do this as some
> kind of crazy byte-by-byte copy_to_user() emulation.
>
> Do the "copy tz to user mode" as individual "put_user()" calls for
> tv_sec/tv_usec/timezone. IOW, there are three words being written to
> user mode, not "two memcpy's".
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.
To handle that case, I'll need 4- and 8- byte versions of put_user_sig
(IIRC vgetcpu uses unsigneds) that check whether their destinations
span page boundaries and complain accordingly, which will end up as
more code than I have now.
--Andy
>
> Other than that, there doesn't seem to be anything wrong.
>
> Linus
>
next prev parent reply other threads:[~2011-10-13 8:40 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 [this message]
2011-10-14 4:46 ` Linus Torvalds
2011-10-14 6:30 ` Andrew Lutomirski
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_7HYnDVUyLA=FQ-qmuh=J=H=JOQTBMP_wt_zwzOfe9-7Hg@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).