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

From: tip-bot for Josh Poimboeuf
Date: Fri Nov 18 2016 - 04:07:05 EST

Commit-ID: c2d75e03d6307bda0e14b616818a6f7b09fd623a
Gitweb: http://git.kernel.org/tip/c2d75e03d6307bda0e14b616818a6f7b09fd623a
Author: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Thu, 17 Nov 2016 09:57:23 -0600
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vince Weaver <vincent.weaver@xxxxxxxxx>
Cc: davej@xxxxxxxxxxxxxxxxx
Cc: dvyukov@xxxxxxxxxx
Link: http://lkml.kernel.org/r/61939c0b2b2d63ce97ba59cba3b00fd47c2962cf.1479398226.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
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);

@@ -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;