Re: [patch V3 15/20] x86/fpu/signal: Change return type of copy_fpregs_to_sigframe() helpers to boolean

[Anders Roxell]

On Tue, 21 Sept 2021 at 22:13, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> On Tue, Sep 21 2021 at 12:58, Anders Roxell wrote:
> > On Wed, 8 Sept 2021 at 15:30, Thomas Gleixner <tglx@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx>
> >
> > 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?

Yes I can try to do that.

Cheers,
Anders