rseq: Use pr_warn_once() when deprecated/unknown ABI flags are encountered

These commits use WARN_ON_ONCE() and kill the offending processes when
deprecated and unknown flags are encountered:

commit c17a6ff93213 ("rseq: Kill process when unknown flags are encountered in ABI structures")
commit 0190e4198e47 ("rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags")

The WARN_ON_ONCE() triggered by userspace input prevents use of
Syzkaller to fuzz the rseq system call.

Replace this WARN_ON_ONCE() by pr_warn_once() messages which contain
actually useful information.

Reported-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20221102130635.7379-1-mathieu.desnoyers@efficios.com

diff --git a/kernel/rseq.c b/kernel/rseq.c
index bda8175..d38ab94 100644 (file)
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -171,12 +171,27 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
        return 0;
 }
 
+static bool rseq_warn_flags(const char *str, u32 flags)
+{
+       u32 test_flags;
+
+       if (!flags)
+               return false;
+       test_flags = flags & RSEQ_CS_NO_RESTART_FLAGS;
+       if (test_flags)
+               pr_warn_once("Deprecated flags (%u) in %s ABI structure", test_flags, str);
+       test_flags = flags & ~RSEQ_CS_NO_RESTART_FLAGS;
+       if (test_flags)
+               pr_warn_once("Unknown flags (%u) in %s ABI structure", test_flags, str);
+       return true;
+}
+
 static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
 {
        u32 flags, event_mask;
        int ret;
 
-       if (WARN_ON_ONCE(cs_flags & RSEQ_CS_NO_RESTART_FLAGS) || cs_flags)
+       if (rseq_warn_flags("rseq_cs", cs_flags))
                return -EINVAL;
 
        /* Get thread flags. */
@@ -184,7 +199,7 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)
        if (ret)
                return ret;
 
-       if (WARN_ON_ONCE(flags & RSEQ_CS_NO_RESTART_FLAGS) || flags)
+       if (rseq_warn_flags("rseq", flags))
                return -EINVAL;
 
        /*