linux-kernel - [PATCH tip/x86/asm] uprobes: __create_xol_area() must nullify xol

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Message-ID: <20160227221128.GA29565@redhat.com>
Date:	Sat, 27 Feb 2016 23:11:28 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andy Lutomirski <tipbot@...or.com>, Ingo Molnar <mingo@...nel.org>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pratyush Anand <panand@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH tip/x86/asm] uprobes: __create_xol_area() must nullify
 xol_mapping.fault

As Jiri pointed out, the 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.

Reported-by: Jiri Olsa <jolsa@...hat.com>
Suggested-by: Jiri Olsa <jolsa@...hat.com>
Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 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])
-- 
2.5.0