Messages in this thread | | | Date | Tue, 21 Sep 2021 10:35:58 -0700 | From | Nick Desaulniers <> | Subject | Re: [patch V3 15/20] x86/fpu/signal: Change return type of copy_fpregs_to_sigframe() helpers to boolean |
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On Tue, Sep 21, 2021 at 12:58:34PM +0200, Anders Roxell wrote: > On Wed, 8 Sept 2021 at 15:30, Thomas Gleixner <tglx@linutronix.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@linutronix.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; > > err |= __put_user(FP_XSTATE_MAGIC2, > (__u32 __user *)(buf + fpu_user_xstate_size));
Thank for the report. Our CI watching tip has also been super red over the past day or so; all boot failures.
Andrew Cooper reported this diff to me on IRC; I tested out the above and it fixes the boot failure for us.
Tested-by: Nick Desaulniers <ndesaulniers@google.com> Link: https://github.com/ClangBuiltLinux/linux/issues/1461
Our CI used -cpu Nehalem for qemu since KVM isn't exposed to the bots on github actions, FWIW. https://github.com/ClangBuiltLinux/boot-utils/blob/2edbca214f9a4cabd3f138ea029015d6cf52d110/boot-qemu.sh#L278-L288
> > > > Cheers, > Anders > [1] http://ix.io/3zxf > > > --- > > arch/x86/kernel/fpu/signal.c | 17 +++++++++-------- > > 1 file changed, 9 insertions(+), 8 deletions(-) > > > > --- a/arch/x86/kernel/fpu/signal.c > > +++ b/arch/x86/kernel/fpu/signal.c > > @@ -65,7 +65,7 @@ static inline int check_xstate_in_sigfra > > /* > > * Signal frame handlers. > > */ > > -static inline int save_fsave_header(struct task_struct *tsk, void __user *buf) > > +static inline bool save_fsave_header(struct task_struct *tsk, void __user *buf) > > { > > if (use_fxsr()) { > > struct xregs_state *xsave = &tsk->thread.fpu.state.xsave; > > @@ -82,18 +82,19 @@ static inline int save_fsave_header(stru > > if (__copy_to_user(buf, &env, sizeof(env)) || > > __put_user(xsave->i387.swd, &fp->status) || > > __put_user(X86_FXSR_MAGIC, &fp->magic)) > > - return -1; > > + return false; > > } else { > > struct fregs_state __user *fp = buf; > > u32 swd; > > + > > if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status)) > > - return -1; > > + return false; > > } > > > > - return 0; > > + return true; > > } > > > > -static inline int save_xstate_epilog(void __user *buf, int ia32_frame) > > +static inline bool save_xstate_epilog(void __user *buf, int ia32_frame) > > { > > struct xregs_state __user *x = buf; > > struct _fpx_sw_bytes *sw_bytes; > > @@ -131,7 +132,7 @@ static inline int save_xstate_epilog(voi > > > > err |= __put_user(xfeatures, (__u32 __user *)&x->header.xfeatures); > > > > - return err; > > + return !err; > > } > > > > static inline int copy_fpregs_to_sigframe(struct xregs_state __user *buf) > > @@ -219,10 +220,10 @@ bool copy_fpstate_to_sigframe(void __use > > } > > > > /* Save the fsave header for the 32-bit frames. */ > > - if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf)) > > + if ((ia32_fxstate || !use_fxsr()) && !save_fsave_header(tsk, buf)) > > return false; > > > > - if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate)) > > + if (use_fxsr() && !save_xstate_epilog(buf_fx, ia32_fxstate)) > > return false; > > > > return true; > >
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