linux-kernel - Re: [tip: x86/fpu] x86/fpu/xstate: Define new functions for clearing fpregs and xstates

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Date:   Tue, 29 Nov 2022 13:19:41 +0200
From:   Ivan Zahariev <famzah@...soft.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     linux-tip-commits@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, x86 <x86@...nel.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>
Subject: Re: [tip: x86/fpu] x86/fpu/xstate: Define new functions for clearing
 fpregs and xstates

Hello gentlemen,
Hello Yu-cheng Yu,

Can you please take a look into this bug which syzbot tracked to a 
commit of yours (b860eb8dce5906b14e3a7f3c771e0b3d6ef61b94). Even since 
we switched from kernel 4.14 to 5.15 we are experiencing often random 
segmentation faults with the following error in "dmesg":

    post.sh[2237] bad frame in rt_sigreturn frame:00007ad24b2f8df8 
ip:733cfa4351d1 sp:7ad24b2f9398 orax:ffffffffffffffff in 
libc-2.28.so[733cfa36d000+147000]

Most commonly Bash is getting hit by this problem but other binaries 
also experience the it less often.

Thomas Gleixner has already provided some insight and a simple 
reproducer: 
https://groups.google.com/g/syzkaller-bugs/c/rbdQkahfwE4/m/RyWIrlA0BQAJ

If there is no simple fix, can we simply revert the faulty commit?

Best regards.
--Ivan