linux-kernel - Re: [PATCH] x86: Remove compat vdso support

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Date:	Mon, 10 Mar 2014 17:58:46 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Jones <davej@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	X86 ML <x86@...nel.org>, Stefani Seibold <stefani@...bold.net>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Remove compat vdso support

On Mon, Mar 10, 2014 at 5:38 PM, Dave Jones <davej@...hat.com> wrote:
> On Mon, Mar 10, 2014 at 05:19:27PM -0700, Andy Lutomirski wrote:
>  > On Mon, Mar 10, 2014 at 5:13 PM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>  > > On 03/10/2014 05:12 PM, Andy Lutomirski wrote:
>  > >> The compat vDSO is a complicated hack that's needed to maintain
>  > >> compatibility with a small range of never-released glibc versions.
>  > >>
>  > >> This removes it and replaces it with a much simpler hack: a config
>  > >> option to disable the 32-bit vDSO by default.
>  > >>
>  > >> Signed-off-by: Andy Lutomirski <luto@...capital.net>
>  > >
>  > > Can we verify this works correctly on the affected distributions?
>  >
>  > It works correctly on Fedora 20 32-bit and 64-bit.
>
> I went and dug through the SRPMs at https://archives.fedoraproject.org
> Fedora hasn't ever shipped with COMPAT_VDSO enabled.
> Before FC6 (kernel 2.6.18), the option never existed.
>

What I mean is: a kernel with this patch can boot Fedora 20.

It looks like OpenSUSE 9 is the affected distribution.  I bootstrapped
a minimal OpenSUSE 9 32-bit chroot (filesystem, glibc, ncurses,
readline, bash).  If there's a non-compat vDSO, it says:

Inconsistency detected by ld.so: rtld.c: 1250: dl_main: Assertion
`(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!

With 'echo 0 >/proc/sys/abi/vsyscall32', it works.  With vdso32=2, it
works.  With CONFIG_ENABLE_VDSO32_BY_DEFAULT=n, it works.  I also
checked an unpatched kernel with compat vdso on.  That also works.

So, the upshot of my patch is that the default becomes sane for
everyone except users of OpenSUSE 9 and similar.  OpenSUSE 9 users
will need to fiddle with their settings or config.

And it looks like I need to spruce up virtme a bit to make this kind
of testing easier :)

I'll respin the patch to note that OpenSUSE 9 is affected.

NB: I've only tested a 64-bit kernel.  Testing a 32-bit kernel will
involve considerably more effort.

>         Dave
>

-- 
Andy Lutomirski
AMA Capital Management, LLC
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