linux-kernel - Re: [patch V3 15/20] x86/fpu/signal: Change return type of copy_fpregs_to

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Message-ID: <871r5h7km4.ffs@tglx>
Date:   Tue, 21 Sep 2021 22:13:23 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tony Luck <tony.luck@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Peter Ziljstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [patch V3 15/20] x86/fpu/signal: Change return type of
 copy_fpregs_to_sigframe() helpers to boolean

On Tue, Sep 21 2021 at 12:58, Anders Roxell wrote:
> On Wed, 8 Sept 2021 at 15:30, Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> Now that copy_fpregs_to_sigframe() returns boolean the individual return
>> codes in the related helper functions do not make sense anymore. Change
>> them to return boolean success/fail.
>>
>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>
> When I build and boot (qemu_x86_64) a defconfig kernel on from todays
> next tag next-20210921 I see the following segmentation fault
>
> 2021-09-21T10:11:45 <6>[    1.622922] mount (89) used greatest stack
> depth: 14384 bytes left
> 2021-09-21T10:11:45 <6>[    1.664760] EXT4-fs (sda): re-mounted. Opts:
> (null). Quota mode: none.
> 2021-09-21T10:11:45 <6>[    1.691041] mkdir (92) used greatest stack
> depth: 14312 bytes left
> 2021-09-21T10:11:45 <6>[    1.713201] mount (93) used greatest stack
> depth: 13720 bytes left
> 2021-09-21T10:11:46 Starting syslogd: /etc/init.d/rcS: line 12:   101
> Segmentation fault      $i start
>
>
> I did a bisection and found this as the faulty patch [1]. When I
> revert this patch I can't see the issue.
>
> We noticed that function 'save_xstate_epilog()' changes the polarity
> of its return code for one of the return statements, and for its only
> caller. but not for the other return statement.
>
> I tried this patch and I couldn't see the segmentation fault.
>
> diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> index 445c57c9c539..61eeebc04427 100644
> --- a/arch/x86/kernel/fpu/signal.c
> +++ b/arch/x86/kernel/fpu/signal.c
> @@ -104,7 +104,7 @@ static inline int save_xstate_epilog(void __user
> *buf, int ia32_frame)
>         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
>
>         if (!use_xsave())
> -               return err;
> +               return !err;

Oops. Good catch. Care to send a proper patch for this?

Thanks,

        tglx