linux-kernel - Re: [PATCH] x86/fpu: Simplify fpu__activate_fpstate

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Date:   Sat, 23 Sep 2017 13:29:32 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Kevin Hao <haokexin@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: Re: [PATCH] x86/fpu: Simplify fpu__activate_fpstate_read()


* Ingo Molnar <mingo@...nel.org> wrote:

> 
> * Eric Biggers <ebiggers3@...il.com> wrote:
> 
> > On Fri, Sep 22, 2017 at 07:33:14AM +0200, Ingo Molnar wrote:
> > > 
> > > * Eric Biggers <ebiggers3@...il.com> wrote:
> > > 
> > > > From: Eric Biggers <ebiggers@...gle.com>
> > > > 
> > > > This series fixes the bug found by syzkaller where the ptrace syscall
> > > > can be used to set invalid bits in a task's FPU state.  I also found
> > > > that an equivalent bug was reachable using the sigreturn syscall, so the
> > > > first patch fixes the bug in both cases.
> > > > 
> > > > The other two patches start validating the other parts of the
> > > > xstate_header and make it so that invalid FPU states can no longer be
> > > > abused to leak the FPU registers of other processes.
> > > > 
> > > > Changes since v2:
> > > >     - Use an exception handler to handle invalid FPU states
> > > >       (suggested by Andy Lutomirski)
> > > >     - Check the size of xstate_header.reserved at build time
> > > >       (suggested by Dave Hansen)
> > > > 
> > > > Eric Biggers (3):
> > > >   x86/fpu: don't let userspace set bogus xcomp_bv
> > > >   x86/fpu: tighten validation of user-supplied xstate_header
> > > >   x86/fpu: reinitialize FPU registers if restoring FPU state fails
> > > > 
> > > >  arch/x86/include/asm/fpu/internal.h | 51 +++++++++++--------------------------
> > > >  arch/x86/include/asm/fpu/xstate.h   | 25 ++++++++++++++++++
> > > >  arch/x86/kernel/fpu/regset.c        | 20 +++++++--------
> > > >  arch/x86/kernel/fpu/signal.c        | 15 ++++++++---
> > > >  arch/x86/kernel/fpu/xstate.c        | 27 ++++++++------------
> > > >  arch/x86/mm/extable.c               | 24 +++++++++++++++++
> > > >  6 files changed, 94 insertions(+), 68 deletions(-)
> > > 
> > > Ok - could you please rebase these to to tip:master that is at:
> > > 
> > > 	git git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git master
> > > 
> > > In particular this has a WIP.x86/fpu branch with FPU fixes+changes queued up but 
> > > not merged upstream (yet), which conflict with these changes. I'd like to merge 
> > > them all together.
> > > 
> > 
> > Working on it, but there is a problem with current tip.  PTRACE_GETREGSET is
> > causing the following warning:
> 
> Yes, the warning should be harmless, and I fixed it locally earlier today - does 
> the patch below solve it for you as well?

Note that this fix is now part of tip:master as well, so if you re-test -tip you 
should get all the latest fixes as well (including yours!).

Thanks,

	Ingo