Messages in this thread Patch in this message | | | Date | Thu, 21 Jun 2018 10:44:37 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [PATCH v2] rseq: Avoid infinite recursion when delivering SIGSEGV |
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----- On Jun 21, 2018, at 7:54 AM, Will Deacon will.deacon@arm.com wrote:
> When delivering a signal to a task that is using rseq, we call into > __rseq_handle_notify_resume() so that the registers pushed in the > sigframe are updated to reflect the state of the restartable sequence > (for example, ensuring that the signal returns to the abort handler if > necessary). > > However, if the rseq management fails due to an unrecoverable fault when > accessing userspace or certain combinations of RSEQ_CS_* flags, then we > will attempt to deliver a SIGSEGV. This has the potential for infinite > recursion if the rseq code continuously fails on signal delivery. > > Avoid this problem by using force_sigsegv() instead of force_sig(), which > is explicitly designed to reset the SEGV handler to SIG_DFL in the case > of a recursive fault. In doing so, remove rseq_signal_deliver() from the > internal rseq API and have an optional struct ksignal * parameter to > rseq_handle_notify_resume() instead. > > Signed-off-by: Will Deacon <will.deacon@arm.com> > --- > > RFC v1 -> v2: Kill rseq_signal_deliver()
I actually meant to kill _rseq_handle_notify_resume introduced by your patch, not rseq_signal_deliver().
Please keep rseq_signal_deliver() as a static inline, and just remove the _rseq_handle_notify_resume() by changing the signature of rseq_handle_notify_resume to take an extra sig argument (which can be NULL).
Thanks,
Mathieu
> > arch/arm/kernel/signal.c | 4 ++-- > arch/powerpc/kernel/signal.c | 4 ++-- > arch/x86/entry/common.c | 2 +- > arch/x86/kernel/signal.c | 2 +- > include/linux/sched.h | 27 ++++++++++++--------------- > kernel/rseq.c | 7 ++++--- > 6 files changed, 22 insertions(+), 24 deletions(-) > > diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c > index f09e9d66d605..184f69dcb9f2 100644 > --- a/arch/arm/kernel/signal.c > +++ b/arch/arm/kernel/signal.c > @@ -544,7 +544,7 @@ static void handle_signal(struct ksignal *ksig, struct > pt_regs *regs) > * Increment event counter and perform fixup for the pre-signal > * frame. > */ > - rseq_signal_deliver(regs); > + rseq_handle_notify_resume(ksig, regs); > > /* > * Set up the stack frame > @@ -666,7 +666,7 @@ do_work_pending(struct pt_regs *regs, unsigned int > thread_flags, int syscall) > } else { > clear_thread_flag(TIF_NOTIFY_RESUME); > tracehook_notify_resume(regs); > - rseq_handle_notify_resume(regs); > + rseq_handle_notify_resume(NULL, regs); > } > } > local_irq_disable(); > diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c > index 17fe4339ba59..88bdf243a5bd 100644 > --- a/arch/powerpc/kernel/signal.c > +++ b/arch/powerpc/kernel/signal.c > @@ -134,7 +134,7 @@ static void do_signal(struct task_struct *tsk) > /* Re-enable the breakpoints for the signal stack */ > thread_change_pc(tsk, tsk->thread.regs); > > - rseq_signal_deliver(tsk->thread.regs); > + rseq_handle_notify_resume(&ksig, tsk->thread.regs); > > if (is32) { > if (ksig.ka.sa.sa_flags & SA_SIGINFO) > @@ -170,7 +170,7 @@ void do_notify_resume(struct pt_regs *regs, unsigned long > thread_info_flags) > if (thread_info_flags & _TIF_NOTIFY_RESUME) { > clear_thread_flag(TIF_NOTIFY_RESUME); > tracehook_notify_resume(regs); > - rseq_handle_notify_resume(regs); > + rseq_handle_notify_resume(NULL, regs); > } > > user_enter(); > diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c > index 92190879b228..3b2490b81918 100644 > --- a/arch/x86/entry/common.c > +++ b/arch/x86/entry/common.c > @@ -164,7 +164,7 @@ static void exit_to_usermode_loop(struct pt_regs *regs, u32 > cached_flags) > if (cached_flags & _TIF_NOTIFY_RESUME) { > clear_thread_flag(TIF_NOTIFY_RESUME); > tracehook_notify_resume(regs); > - rseq_handle_notify_resume(regs); > + rseq_handle_notify_resume(NULL, regs); > } > > if (cached_flags & _TIF_USER_RETURN_NOTIFY) > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > index 445ca11ff863..8affeeb74935 100644 > --- a/arch/x86/kernel/signal.c > +++ b/arch/x86/kernel/signal.c > @@ -692,7 +692,7 @@ setup_rt_frame(struct ksignal *ksig, struct pt_regs *regs) > * Increment event counter and perform fixup for the pre-signal > * frame. > */ > - rseq_signal_deliver(regs); > + rseq_handle_notify_resume(ksig, regs); > > /* Set up the stack frame */ > if (is_ia32_frame(ksig)) { > diff --git a/include/linux/sched.h b/include/linux/sched.h > index 87bf02d93a27..fd23a540cd8d 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1799,20 +1799,19 @@ static inline void rseq_set_notify_resume(struct > task_struct *t) > set_tsk_thread_flag(t, TIF_NOTIFY_RESUME); > } > > -void __rseq_handle_notify_resume(struct pt_regs *regs); > +void __rseq_handle_notify_resume(struct ksignal *sig, struct pt_regs *regs); > > -static inline void rseq_handle_notify_resume(struct pt_regs *regs) > +static inline void rseq_handle_notify_resume(struct ksignal *ksig, > + struct pt_regs *regs) > { > - if (current->rseq) > - __rseq_handle_notify_resume(regs); > -} > + if (ksig) { > + preempt_disable(); > + __set_bit(RSEQ_EVENT_SIGNAL_BIT, ¤t->rseq_event_mask); > + preempt_enable(); > + } > > -static inline void rseq_signal_deliver(struct pt_regs *regs) > -{ > - preempt_disable(); > - __set_bit(RSEQ_EVENT_SIGNAL_BIT, ¤t->rseq_event_mask); > - preempt_enable(); > - rseq_handle_notify_resume(regs); > + if (current->rseq) > + __rseq_handle_notify_resume(ksig, regs); > } > > /* rseq_preempt() requires preemption to be disabled. */ > @@ -1864,10 +1863,8 @@ static inline void rseq_execve(struct task_struct *t) > static inline void rseq_set_notify_resume(struct task_struct *t) > { > } > -static inline void rseq_handle_notify_resume(struct pt_regs *regs) > -{ > -} > -static inline void rseq_signal_deliver(struct pt_regs *regs) > +static inline void rseq_handle_notify_resume(struct ksignal *ksig, > + struct pt_regs *regs) > { > } > static inline void rseq_preempt(struct task_struct *t) > diff --git a/kernel/rseq.c b/kernel/rseq.c > index ae306f90c514..22b6acf1ad63 100644 > --- a/kernel/rseq.c > +++ b/kernel/rseq.c > @@ -251,10 +251,10 @@ static int rseq_ip_fixup(struct pt_regs *regs) > * respect to other threads scheduled on the same CPU, and with respect > * to signal handlers. > */ > -void __rseq_handle_notify_resume(struct pt_regs *regs) > +void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs) > { > struct task_struct *t = current; > - int ret; > + int ret, sig; > > if (unlikely(t->flags & PF_EXITING)) > return; > @@ -268,7 +268,8 @@ void __rseq_handle_notify_resume(struct pt_regs *regs) > return; > > error: > - force_sig(SIGSEGV, t); > + sig = ksig ? ksig->sig : 0; > + force_sigsegv(sig, t); > } > > #ifdef CONFIG_DEBUG_RSEQ > -- > 2.1.4
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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