rseq: Avoid infinite recursion when delivering SIGSEGV
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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: peterz@infradead.org
Cc: paulmck@linux.vnet.ibm.com
Cc: boqun.feng@gmail.com
Link: https://lkml.kernel.org/r/1529664307-983-1-git-send-email-will.deacon@arm.com
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index f09e9d66..dec130e 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -544,7 +544,7 @@
* 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
@@ -666,7 +666,7 @@
} 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 17fe433..b3e8db3 100644
--- a/arch/powerpc/kernel/signal.c
+++ b/arch/powerpc/kernel/signal.c
@@ -134,7 +134,7 @@
/* 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)
@@ -170,7 +170,7 @@
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 9219087..3b2490b 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -164,7 +164,7 @@
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 445ca11..92a3b31 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -692,7 +692,7 @@
* 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 c188264..9256118 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1799,20 +1799,22 @@
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_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. */
@@ -1861,10 +1863,12 @@
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_handle_notify_resume(struct ksignal *ksig,
+ 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 ae306f9..22b6acf 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -251,10 +251,10 @@
* 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 @@
return;
error:
- force_sig(SIGSEGV, t);
+ sig = ksig ? ksig->sig : 0;
+ force_sigsegv(sig, t);
}
#ifdef CONFIG_DEBUG_RSEQ