Add a might_fault() check to validate that the perf sys_enter/sys_exit
probe callbacks are indeed called from a context where page faults can
be handled.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Michael Jeanson <mjeanson@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Yonghong Song <yhs@fb.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: bpf@vger.kernel.org
Cc: Joel Fernandes <joel@joelfernandes.org>
---
 include/trace/perf.h          | 1 +
 kernel/trace/trace_syscalls.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/include/trace/perf.h b/include/trace/perf.h
index 5650c1bad088..321bfd7919f6 100644
--- a/include/trace/perf.h
+++ b/include/trace/perf.h
@@ -84,6 +84,7 @@ perf_trace_##call(void *__data, proto)					\
 	u64 __count __attribute__((unused));				\
 	struct task_struct *__task __attribute__((unused));		\
 									\
+	might_fault();							\
 	guard(preempt_notrace)();					\
 	do_perf_trace_##call(__data, args);				\
 }
diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index 0430890cbb42..53faa791c735 100644
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -600,6 +600,7 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
 	 * Syscall probe called with preemption enabled, but the ring
 	 * buffer and per-cpu data require preemption to be disabled.
 	 */
+	might_fault();
 	guard(preempt_notrace)();
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
@@ -706,6 +707,7 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
 	 * Syscall probe called with preemption enabled, but the ring
 	 * buffer and per-cpu data require preemption to be disabled.
 	 */
+	might_fault();
 	guard(preempt_notrace)();
 
 	syscall_nr = trace_get_syscall_nr(current, regs);
-- 
2.39.2