linux-kernel - [PATCH 2/7] uprobes: change read_opcode() to use FOLL

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Message-ID: <20120529192759.GB8057@redhat.com>
Date:	Tue, 29 May 2012 21:27:59 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <anton@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/7] uprobes: change read_opcode() to use FOLL_FORCE

set_orig_insn()->read_opcode() should not fail if the probed task
did mprotect() after uprobe_register(), change it to use FOLL_FORCE.
Without FOLL_WRITE this doesn't have any "side" effect but allows
to read the !VM_READ memory.

There is another reason for this change, we are going to use
is_swbp_at_addr() from handle_swbp() which can race with another
thread doing mprotect().

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/events/uprobes.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d0f5ec0..a0dbc87 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -312,7 +312,7 @@ static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_
 	void *vaddr_new;
 	int ret;
 
-	ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL);
+	ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
 	if (ret <= 0)
 		return ret;
 
-- 
1.5.5.1


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