rseq: Optimise rseq_get_rseq_cs() and clear_rseq_cs()

Commit ec9c82e03a74 ("rseq: uapi: Declare rseq_cs field as union,
update includes") added regressions for our servers.

Using copy_from_user() and clear_user() for 64bit values
is suboptimal.

We can use faster put_user() and get_user() on 64bit arches.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lkml.kernel.org/r/20210413203352.71350-4-eric.dumazet@gmail.com

diff --git a/kernel/rseq.c b/kernel/rseq.c
index cfe01ab..35f7bd0 100644 (file)
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -127,8 +127,13 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs)
        u32 sig;
        int ret;
 
+#ifdef CONFIG_64BIT
+       if (get_user(ptr, &t->rseq->rseq_cs.ptr64))
+               return -EFAULT;
+#else
        if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr)))
                return -EFAULT;
+#endif
        if (!ptr) {
                memset(rseq_cs, 0, sizeof(*rseq_cs));
                return 0;
@@ -211,9 +216,13 @@ static int clear_rseq_cs(struct task_struct *t)
         *
         * Set rseq_cs to NULL.
         */
+#ifdef CONFIG_64BIT
+       return put_user(0UL, &t->rseq->rseq_cs.ptr64);
+#else
        if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64)))
                return -EFAULT;
        return 0;
+#endif
 }
 
 /*