[PATCH for 4.18 2/6] rseq: use get_user/put_user rather than __get_user/__put_user

[Mathieu Desnoyers]

In preparation to use __u64 for the rseq_cs pointer field, 32-bit
architectures need to read this 64-bit value located in user-space
addresses.

__get_user is used to read this value, given that its access check has
already been performed with access_ok() on rseq registration.

arm does not implement 8-byte __get_user. Rather than trying to
improve __get_user on ARM, use get_user/put_user across rseq instead.

If those end up showing up in benchmarks, the proper approach would be to
use user_access_begin() / unsafe_get/put_user() / user_access_end()
anyway.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
CC: Thomas Gleixner <t...@linutronix.de>
Cc: Joel Fernandes <joe...@google.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Dave Watson <davejwat...@fb.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Andi Kleen <a...@firstfloor.org>
Cc: "H . Peter Anvin" <h...@zytor.com>
Cc: Chris Lameter <c...@linux.com>
Cc: Russell King <li...@arm.linux.org.uk>
Cc: Andrew Hunter <a...@google.com>
Cc: Michael Kerrisk <mtk.manpa...@gmail.com>
Cc: "Paul E . McKenney" <paul...@linux.vnet.ibm.com>
Cc: Paul Turner <p...@google.com>
Cc: Boqun Feng <boqun.f...@gmail.com>
Cc: Josh Triplett <j...@joshtriplett.org>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Ben Maurer <bmau...@fb.com>
Cc: linux-...@vger.kernel.org
CC: linux-arm-ker...@lists.infradead.org
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
---
 kernel/rseq.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/rseq.c b/kernel/rseq.c
index 16b38c5342f9..2c8463acb50d 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -85,9 +85,9 @@ static int rseq_update_cpu_id(struct task_struct *t)
 {
        u32 cpu_id = raw_smp_processor_id();
 
-       if (__put_user(cpu_id, &t->rseq->cpu_id_start))
+       if (put_user(cpu_id, &t->rseq->cpu_id_start))
                return -EFAULT;
-       if (__put_user(cpu_id, &t->rseq->cpu_id))
+       if (put_user(cpu_id, &t->rseq->cpu_id))
                return -EFAULT;
        trace_rseq_update(t);
        return 0;
@@ -100,14 +100,14 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t)
        /*
         * Reset cpu_id_start to its initial state (0).
         */
-       if (__put_user(cpu_id_start, &t->rseq->cpu_id_start))
+       if (put_user(cpu_id_start, &t->rseq->cpu_id_start))
                return -EFAULT;
        /*
         * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming
         * in after unregistration can figure out that rseq needs to be
         * registered again.
         */
-       if (__put_user(cpu_id, &t->rseq->cpu_id))
+       if (put_user(cpu_id, &t->rseq->cpu_id))
                return -EFAULT;
        return 0;
 }
@@ -120,7 +120,7 @@ static int rseq_get_rseq_cs(struct task_struct *t, struct 
rseq_cs *rseq_cs)
        u32 sig;
        int ret;
 
-       ret = __get_user(ptr, &t->rseq->rseq_cs);
+       ret = get_user(ptr, &t->rseq->rseq_cs);
        if (ret)
                return ret;
        if (!ptr) {
@@ -163,7 +163,7 @@ static int rseq_need_restart(struct task_struct *t, u32 
cs_flags)
        int ret;
 
        /* Get thread flags. */
-       ret = __get_user(flags, &t->rseq->flags);
+       ret = get_user(flags, &t->rseq->flags);
        if (ret)
                return ret;
 
@@ -203,7 +203,7 @@ static int clear_rseq_cs(struct task_struct *t)
         *
         * Set rseq_cs to NULL with single-copy atomicity.
         */
-       return __put_user(0UL, &t->rseq->rseq_cs);
+       return put_user(0UL, &t->rseq->rseq_cs);
 }
 
 /*
-- 
2.11.0