linux-kernel - [PATCH for 4.18 2/6] rseq: use get_user/put_user rather than __get_user/__put

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Message-Id: <20180708210330.27324-3-mathieu.desnoyers@efficios.com>
Date:   Sun,  8 Jul 2018 17:03:26 -0400
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
        Ben Maurer <bmaurer@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Andrew Hunter <ahh@...gle.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH for 4.18 2/6] rseq: use get_user/put_user rather than __get_user/__put_user

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.desnoyers@...icios.com>
CC: Thomas Gleixner <tglx@...utronix.de>
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Dave Watson <davejwatson@...com>
Cc: Will Deacon <will.deacon@....com>
Cc: Andi Kleen <andi@...stfloor.org>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: Chris Lameter <cl@...ux.com>
Cc: Russell King <linux@....linux.org.uk>
Cc: Andrew Hunter <ahh@...gle.com>
Cc: Michael Kerrisk <mtk.manpages@...il.com>
Cc: "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Paul Turner <pjt@...gle.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Josh Triplett <josh@...htriplett.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Maurer <bmaurer@...com>
Cc: linux-api@...r.kernel.org
CC: linux-arm-kernel@...ts.infradead.org
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-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