From: Linus Torvalds <torvalds@linux-foundation.org>
To: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Gerald Schaefer <gerald.schaefer@de.ibm.com>,
linux-kernel@vger.kernel.org, schwidefsky@de.ibm.com,
heiko.carstens@de.ibm.com
Subject: Re: [BUG] binfmt_elf: get_user() called in vma_dump_size() after set_fs(KERNEL_DS)
Date: Fri, 6 Feb 2009 14:19:31 -0800 (PST) [thread overview]
Message-ID: <alpine.LFD.2.00.0902061416070.3048@localhost.localdomain> (raw)
In-Reply-To: <20090206220717.AE750FC3AD@magilla.sf.frob.com>
On Fri, 6 Feb 2009, Roland McGrath wrote:
>
> set_fs is quite cheap at least on most machines. So a pair of set_fs calls
> around that get_user call doesn't seem so bad. OTOH, on the machines where
> this actually matters at all (maybe just sparc, arm, s390?) it is
> presumably (much?) more costly. But it seems like the best solution, and
> certainly is straightforward.
Yes, I suspect just surrounding the load with set_fs(USER_DS) and then
set_fs(KERNEL_DS) to put it back is likely the right thing to do.
The address is "safe" in that it does come from the vma, but we obviously
do play games with things like the call gate mappings etc. Should we also
perhaps do this only if the vma is marked readable and executable? That
way we could avoid taking unnecessary faults there.
Probably doesn't really matter.
Linus
next prev parent reply other threads:[~2009-02-06 22:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-06 17:10 Gerald Schaefer
2009-02-06 21:44 ` Andrew Morton
2009-02-06 21:57 ` Linus Torvalds
2009-02-06 22:07 ` Roland McGrath
2009-02-06 22:18 ` David Miller
2009-02-06 22:19 ` Linus Torvalds [this message]
2009-02-07 1:55 ` [PATCH] elf core dump: fix get_user use Roland McGrath
2009-02-07 1:55 ` [BUG] binfmt_elf: get_user() called in vma_dump_size() after set_fs(KERNEL_DS) Roland McGrath
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