[tip:x86/asm] uprobes: __create_xol_area() must nullify xol_mapping.fault

[tip-bot for Oleg Nesterov <tipbot@zytor.com>]

Commit-ID:  869ae76147ffdf21ad24f0e599303cd58a2bb39f
Gitweb:     http://git.kernel.org/tip/869ae76147ffdf21ad24f0e599303cd58a2bb39f
Author:     Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sat, 27 Feb 2016 23:11:28 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 29 Feb 2016 08:47:51 +0100

uprobes: __create_xol_area() must nullify xol_mapping.fault

As Jiri pointed out, this recent commit:

 f872f5400cc0 ("mm: Add a vm_special_mapping.fault() method")

breaks uprobes: __create_xol_area() doesn't initialize the new ->fault()
method and this obviously leads to kernel crash when the application
tries to execute the probed insn after bp hit.

We probably want to add uprobes_special_mapping_fault(), this allows to
turn xol_area->xol_mapping into a single instance of vm_special_mapping.
But we need a simple fix, so lets change __create_xol() to nullify the
new member as Jiri suggests.

Suggested-by: Jiri Olsa <jolsa@redhat.com>
Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <tipbot@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160227221128.GA29565@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/events/uprobes.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 0167679..5f6ce93 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1178,6 +1178,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr)
 		goto free_area;
 
 	area->xol_mapping.name = "[uprobes]";
+	area->xol_mapping.fault = NULL;
 	area->xol_mapping.pages = area->pages;
 	area->pages[0] = alloc_page(GFP_HIGHUSER);
 	if (!area->pages[0])