From: Ingo Molnar <mingo@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>,
"x86@kernel.org" <x86@kernel.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: rwx mapping between ex_table and rodata
Date: Fri, 25 Sep 2015 09:22:59 +0200 [thread overview]
Message-ID: <20150925072259.GA17639@gmail.com> (raw)
In-Reply-To: <CAGXu5j+tTR=x9RTOFvqQP7+W7DFR6N+GUP__uvAicrfTBU1B7w@mail.gmail.com>
* Kees Cook <keescook@chromium.org> wrote:
> On Thu, Sep 24, 2015 at 1:26 PM, Stephen Smalley <sds@tycho.nsa.gov> wrote:
> > Hi,
> >
> > With the attached config and 4.3-rc2 on x86_64, I see the following in /sys/kernel/debug/kernel_page_tables:
> > ...
> > ---[ High Kernel Mapping ]---
> > 0xffffffff80000000-0xffffffff81000000 16M pmd
> > 0xffffffff81000000-0xffffffff81600000 6M ro PSE GLB x pmd
> > 0xffffffff81600000-0xffffffff81775000 1492K ro GLB x pte
> > 0xffffffff81775000-0xffffffff81800000 556K RW GLB x pte
> > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > 0xffffffff81800000-0xffffffff81a00000 2M ro PSE GLB NX pmd
> > 0xffffffff81a00000-0xffffffff81b43000 1292K ro GLB NX pte
> > 0xffffffff81b43000-0xffffffff82000000 4852K RW GLB NX pte
> > 0xffffffff82000000-0xffffffff82200000 2M RW PSE GLB NX pmd
> > 0xffffffff82200000-0xffffffffa0000000 478M pmd
> > ...
> >
> > This region seems to be between the end of ex_table and the start of rodata,
> > $ objdump -x vmlinux | sort
> > ...
> > ffffffff817728b0 g __ex_table 0000000000000000 __start___ex_table
> > ffffffff817728b0 l d __ex_table 0000000000000000 __ex_table
> > ffffffff81774998 g __ex_table 0000000000000000 __stop___ex_table
> > ffffffff81800000 g .rodata 0000000000000000 __start_rodata
> > ffffffff81800000 l d .rodata 0000000000000000 .rodata
> > ...
> >
> > $ readelf -a vmlinux
> > ...
> > Section Headers:
> > [Nr] Name Type Address Offset
> > Size EntSize Flags Link Info Align
> > ...
> > [ 3] __ex_table PROGBITS ffffffff817728b0 009728b0
> > 00000000000020e8 0000000000000000 A 0 0 8
> > [ 4] .rodata PROGBITS ffffffff81800000 00a00000
> > 00000000002eefd2 0000000000000000 A 0 0 64
> > ...
> >
> > I see a similar rwx mapping with the stock Fedora kernels (e.g. 4.1.6), so it isn't new to 4.3.
>
> To me it looks like another alignment/padding issue like got fixed
> before. The space between __ex_table and rodata is (seems?) unused, so
> the default page table permissions end up being W+X. Can we fix the
> default to be NX instead? It'll make these bugs stay gone.
Yeah. Wanna send a patch for that?
Thanks,
Ingo
next prev parent reply other threads:[~2015-09-25 7:23 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-24 20:23 rwx mapping between ex_table and rodata Stephen Smalley
2015-09-24 20:26 ` Fwd: " Stephen Smalley
2015-09-24 22:25 ` Kees Cook
2015-09-25 7:22 ` Ingo Molnar [this message]
2015-09-26 16:49 ` Kees Cook
2015-09-28 21:16 ` H. Peter Anvin
2015-09-28 22:05 ` Kees Cook
2015-09-28 22:20 ` H. Peter Anvin
2015-09-25 7:25 ` Ingo Molnar
2015-09-28 14:11 ` Stephen Smalley
2015-09-28 18:27 ` Kees Cook
2015-10-01 7:09 ` Ingo Molnar
2015-10-01 9:03 ` Thomas Gleixner
2015-10-01 9:12 ` Ingo Molnar
2015-10-01 17:45 ` Kees Cook
2015-10-02 7:19 ` Ingo Molnar
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