----- On Jun 20, 2018, at 12:36 PM, Will Deacon [email protected] 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.
Your approach looks good. One nit below implementation-wise: > > Signed-off-by: Will Deacon <[email protected]> > --- > > Sending as an RFC since I only spotted this via code inspection and haven't > tried to trigger it yet. > > arch/arm/kernel/signal.c | 2 +- > arch/powerpc/kernel/signal.c | 2 +- > arch/x86/kernel/signal.c | 2 +- > include/linux/sched.h | 20 ++++++++++++++------ > kernel/rseq.c | 7 ++++--- > 5 files changed, 21 insertions(+), 12 deletions(-) > > diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c > index f09e9d66d605..6434a62591e8 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_signal_deliver(ksig, regs); > > /* > * Set up the stack frame > diff --git a/arch/powerpc/kernel/signal.c b/arch/powerpc/kernel/signal.c > index 17fe4339ba59..af822e764569 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_signal_deliver(&ksig, tsk->thread.regs); > > if (is32) { > if (ksig.ka.sa.sa_flags & SA_SIGINFO) > diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c > index 445ca11ff863..92a3b312a53c 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_signal_deliver(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..277f8ccb0661 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -1799,20 +1799,27 @@ 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); > + __rseq_handle_notify_resume(ksig, regs); > +} > + > +static inline void rseq_handle_notify_resume(struct pt_regs *regs) > +{ > + _rseq_handle_notify_resume(NULL, regs); > } If we add _rseq_handle_notify_resume() here, we'd need the CONFIG_RSEQ=n code to also have an empty static inline for it. So I'm not sure we want all 3 of: void __rseq_handle_notify_resume(struct ksignal *sig, struct pt_regs *regs); static inline void _rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs) static inline void rseq_handle_notify_resume(struct pt_regs *regs) Instead, can we just have: __rseq_handle_notify_resume(struct ksignal *sig, struct pt_regs *regs); static inline void rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs) and change the callers to rseq_handle_notify_resume to pass a NULL pointer when they are not within signal delivery ? Thanks, Mathieu > > -static inline void rseq_signal_deliver(struct pt_regs *regs) > +static inline void rseq_signal_deliver(struct ksignal *ksig, > + struct pt_regs *regs) > { > preempt_disable(); > __set_bit(RSEQ_EVENT_SIGNAL_BIT, ¤t->rseq_event_mask); > preempt_enable(); > - rseq_handle_notify_resume(regs); > + _rseq_handle_notify_resume(ksig, regs); > } > > /* rseq_preempt() requires preemption to be disabled. */ > @@ -1867,7 +1874,8 @@ 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_signal_deliver(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
