linux-kernel - Re: [patch 0/8] x86/fpu: Mop up XSAVES and related damage

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Date:   Wed, 2 Jun 2021 14:28:00 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [patch 0/8] x86/fpu: Mop up XSAVES and related damage

On 6/2/2021 2:55 AM, Thomas Gleixner wrote:
> syszbot reported a warnon for XRSTOR raising #GP:
> 
>   https://lore.kernel.org/r/0000000000004c453905c30f8334@google.com
> 
> with a syzcaller reproducer and a conclusive bisect result.
> 
> It took a while to destill a simple C reproducer out of it which allowed to
> pin point the root cause: The recent addition of supervisor XSTATEs broke
> the signal restore path for the case where the signal handler wreckaged the
> XSTATE on stack because it does not sanitize the XSTATE header which causes
> a subsequent XRSTOR to fail and #GP.
> 
> The following series addresses the problem and fixes related issues which
> were found while inspecting the related changes.
> 
> Thanks to Andy and Dave for working on this with me!
> 
> Thanks,
> 
> 	tglx
> ---
>   arch/x86/include/asm/fpu/xstate.h                     |    4
>   arch/x86/kernel/fpu/core.c                            |   62 ++++++---
>   arch/x86/kernel/fpu/regset.c                          |   43 ++----
>   arch/x86/kernel/fpu/signal.c                          |   30 +++-
>   arch/x86/kernel/fpu/xstate.c                          |   95 +++++----------
>   b/tools/testing/selftests/x86/corrupt_xstate_header.c |  114 ++++++++++++++++++
>   tools/testing/selftests/x86/Makefile                  |    3
>   7 files changed, 234 insertions(+), 117 deletions(-)
> 

With the series applied, glibc pkey test fails sometimes.  I will try to 
find out the cause.

The test:

https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/tst-pkey.c

The output:

error: ../sysdeps/unix/sysv/linux/tst-pkey.c:161: not true: 
!check_page_access (i, false)
error: ../sysdeps/unix/sysv/linux/tst-pkey.c:162: not true: 
!check_page_access (i, true)
error: ../sysdeps/unix/sysv/linux/tst-pkey.c:161: not true: 
!check_page_access (i, false)
error: ../sysdeps/unix/sysv/linux/tst-pkey.c:162: not true: 
!check_page_access (i, true)
error: ../sysdeps/unix/sysv/linux/tst-pkey.c:161: not true: 
!check_page_access (i, false)
error: ../sysdeps/unix/sysv/linux/tst-pkey.c:162: not true: 
!check_page_access (i, true)
../sysdeps/unix/sysv/linux/tst-pkey.c:238: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
../sysdeps/unix/sysv/linux/tst-pkey.c:238: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
../sysdeps/unix/sysv/linux/tst-pkey.c:238: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
../sysdeps/unix/sysv/linux/tst-pkey.c:242: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
../sysdeps/unix/sysv/linux/tst-pkey.c:242: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
../sysdeps/unix/sysv/linux/tst-pkey.c:242: numeric comparison failure
    left: 0 (0x0); from: result->access_rights[i]
   right: 1 (0x1); from: PKEY_DISABLE_ACCESS
error: 12 test failures