[tip:x86/urgent] x86/stacktrace: Prevent access_ok() warnings in arch_stack_walk_user()

[tip-bot for Eiichi Tsukata <tipbot@zytor.com>]

Commit-ID:  2af7c85714d8cafadf925d55441458eae312cd6b
Gitweb:     https://git.kernel.org/tip/2af7c85714d8cafadf925d55441458eae312cd6b
Author:     Eiichi Tsukata <devel@etsukata.com>
AuthorDate: Mon, 22 Jul 2019 17:32:16 +0900
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Mon, 22 Jul 2019 10:42:36 +0200

x86/stacktrace: Prevent access_ok() warnings in arch_stack_walk_user()

When arch_stack_walk_user() is called from atomic contexts, access_ok() can
trigger the following warning if compiled with CONFIG_DEBUG_ATOMIC_SLEEP=y.

Reproducer:

  // CONFIG_DEBUG_ATOMIC_SLEEP=y
  # cd /sys/kernel/debug/tracing
  # echo 1 > options/userstacktrace
  # echo 1 > events/irq/irq_handler_entry/enable

  WARNING: CPU: 0 PID: 2649 at arch/x86/kernel/stacktrace.c:103 arch_stack_walk_user+0x6e/0xf6
  CPU: 0 PID: 2649 Comm: bash Not tainted 5.3.0-rc1+ #99
  RIP: 0010:arch_stack_walk_user+0x6e/0xf6
  Call Trace:
   <IRQ>
   stack_trace_save_user+0x10a/0x16d
   trace_buffer_unlock_commit_regs+0x185/0x240
   trace_event_buffer_commit+0xec/0x330
   trace_event_raw_event_irq_handler_entry+0x159/0x1e0
   __handle_irq_event_percpu+0x22d/0x440
   handle_irq_event_percpu+0x70/0x100
   handle_irq_event+0x5a/0x8b
   handle_edge_irq+0x12f/0x3f0
   handle_irq+0x34/0x40
   do_IRQ+0xa6/0x1f0
   common_interrupt+0xf/0xf
   </IRQ>

Fix it by calling __range_not_ok() directly instead of access_ok() as
copy_from_user_nmi() does. This is fine here because the actual copy is
inside a pagefault disabled region.

Reported-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Eiichi Tsukata <devel@etsukata.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190722083216.16192-2-devel@etsukata.com

---
 arch/x86/kernel/stacktrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 4f36d3241faf..2d6898c2cb64 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -100,7 +100,7 @@ copy_stack_frame(const void __user *fp, struct stack_frame_user *frame)
 {
 	int ret;
 
-	if (!access_ok(fp, sizeof(*frame)))
+	if (__range_not_ok(fp, sizeof(*frame), TASK_SIZE))
 		return 0;
 
 	ret = 1;