linux-kernel - Re: [3.1 patch] x86: default to vsyscall=native

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Message-ID: <CAObL_7FJy=BFmtuTd+CE_uF2+ra6LnQWGUp=g+1py_V9ukYvJg@mail.gmail.com>
Date:	Thu, 6 Oct 2011 11:16:59 -0700
From:	Andrew Lutomirski <luto@....edu>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Adrian Bunk <bunk@...sta.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [3.1 patch] x86: default to vsyscall=native

On Thu, Oct 6, 2011 at 8:37 AM, richard -rw- weinberger
<richard.weinberger@...il.com> wrote:
> On Thu, Oct 6, 2011 at 5:06 AM, Andrew Lutomirski <luto@....edu> wrote:
>> I'll see how ugly the patch to get this all correct is.  It may not be
>> all that pretty because we won't be able to use sys_gettimeofday
>> anymore.
>
> BTW: The attached program triggers the issue.
>
> on 3.1-rc8+:
> # ./sig.dyn
> faulting address: 0xdeadbeef
> # ./sig.static
> [   19.075106] sig.static[863] vsyscall fault (exploit attempt?)
> ip:ffffffffff600000 cs:33 sp:7fff9e53d8c8 ax:ffffffffff600000 si:0
> di:deadbeef
> faulting address: 0x0
>
> I guess UML is not the only user of this feature...

I assume you wrote this to detect the problem :)

Fixing it will be annoying because the attached fancier version needs
to work, too.  I could implement the whole mess in software, but it
might be nicer to arrange for uaccess errors to stash some information
somewhere (like in the thread_struct cr2 variable).

--Andy

View attachment "sig.c" of type "text/x-csrc" (691 bytes)