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Date: Tue, 6 Feb 2018 22:51:32 +0000
From: Luis Henriques <lhenriques@...e.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Greg KH <gregkh@...uxfoundation.org>, X86 ML <x86@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH v4 07/10] x86: narrow out of bounds syscalls to sys_read
under speculation
On Tue, Feb 06, 2018 at 11:48:45AM -0800, Dan Williams wrote:
> On Tue, Feb 6, 2018 at 11:29 AM, Luis Henriques <lhenriques@...e.com> wrote:
> > On Thu, Jan 18, 2018 at 04:02:21PM -0800, Dan Williams wrote:
> >> The syscall table base is a user controlled function pointer in kernel
> >> space. Like, 'get_user, use 'MASK_NOSPEC' to prevent any out of bounds
> >> speculation. While retpoline prevents speculating into the user
> >> controlled target it does not stop the pointer de-reference, the concern
> >> is leaking memory relative to the syscall table base.
> >
> > This patch seems to cause a regression. An easy way to reproduce what
> > I'm seeing is to run the samples/statx/test-statx. Here's what I see
> > when I have this patchset applied:
> >
> > # ./test-statx /tmp
> > statx(/tmp) = -1
> > /tmp: Bad file descriptor
> >
> > Reverting this single patch seems to fix it.
>
> Just to clarify, when you say "this patch" you mean:
>
> 2fbd7af5af86 x86/syscall: Sanitize syscall table de-references
> under speculation
>
> ...not this early MASK_NOSPEC version of the patch, right?
*sigh*
Looks like I spent some good amount of time hunting a non-issue just
because I have enough old branches hanging around to confusing me :-(
Sorry for the noise.
Cheers,
--
Luís
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