linux-kernel - [tip:x86/urgent] x86/unwind: Prevent KASAN false positive warnings in guess unwinder

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Date:   Fri, 18 Nov 2016 01:04:21 -0800
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, eranian@...il.com, acme@...nel.org,
        jpoimboe@...hat.com, linux-kernel@...r.kernel.org,
        vincent.weaver@...ne.edu, mingo@...nel.org, brgerst@...il.com,
        tglx@...utronix.de, bp@...en8.de, luto@...nel.org,
        dvlasenk@...hat.com, torvalds@...ux-foundation.org,
        peterz@...radead.org
Subject: [tip:x86/urgent] x86/unwind: Prevent KASAN false positive warnings
 in guess unwinder

Commit-ID:  c2d75e03d6307bda0e14b616818a6f7b09fd623a
Gitweb:     http://git.kernel.org/tip/c2d75e03d6307bda0e14b616818a6f7b09fd623a
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Thu, 17 Nov 2016 09:57:23 -0600
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 18 Nov 2016 09:38:00 +0100

x86/unwind: Prevent KASAN false positive warnings in guess unwinder

The guess unwinder scans the entire stack, which can cause KASAN
"stack-out-of-bounds" false positive warnings.  Tell KASAN to ignore it.

Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Stephane Eranian <eranian@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Cc: davej@...emonkey.org.uk
Cc: dvyukov@...gle.com
Link: http://lkml.kernel.org/r/61939c0b2b2d63ce97ba59cba3b00fd47c2962cf.1479398226.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/unwind_guess.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
index 2d721e5..b80e8bf 100644
--- a/arch/x86/kernel/unwind_guess.c
+++ b/arch/x86/kernel/unwind_guess.c
@@ -7,11 +7,13 @@
 
 unsigned long unwind_get_return_address(struct unwind_state *state)
 {
+	unsigned long addr = READ_ONCE_NOCHECK(*state->sp);
+
 	if (unwind_done(state))
 		return 0;
 
 	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
-				     *state->sp, state->sp);
+				     addr, state->sp);
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
@@ -23,8 +25,10 @@ bool unwind_next_frame(struct unwind_state *state)
 		return false;
 
 	do {
+		unsigned long addr = READ_ONCE_NOCHECK(*state->sp);
+
 		for (state->sp++; state->sp < info->end; state->sp++)
-			if (__kernel_text_address(*state->sp))
+			if (__kernel_text_address(addr))
 				return true;
 
 		state->sp = info->next_sp;