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Subject[tip:x86/urgent] x86/unwind: Fix guess-unwinder regression
Commit-ID:  55f856e640560494518eaf24fe9d2d2089fba71a
Gitweb: http://git.kernel.org/tip/55f856e640560494518eaf24fe9d2d2089fba71a
Author: Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Sun, 27 Nov 2016 23:13:07 -0600
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 28 Nov 2016 07:47:54 +0100

x86/unwind: Fix guess-unwinder regression

My attempt at fixing some KASAN false positive warnings was rather brain
dead, and it broke the guess unwinder. With frame pointers disabled,
/proc/<pid>/stack is broken:

# cat /proc/1/stack
[<ffffffffffffffff>] 0xffffffffffffffff

Restore the code flow to more closely resemble its previous state, while
still using READ_ONCE_NOCHECK() macros to silence KASAN false positives.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c2d75e03d630 ("x86/unwind: Prevent KASAN false positive warnings in guess unwinder")
Link: http://lkml.kernel.org/r/b824f92c2c22eca5ec95ac56bd2a7c84cf0b9df9.1480309971.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/unwind_guess.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
index b80e8bf..22881dd 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);
+ unsigned long addr;

if (unwind_done(state))
return 0;

+ addr = READ_ONCE_NOCHECK(*state->sp);
+
return ftrace_graph_ret_addr(state->task, &state->graph_idx,
addr, state->sp);
}
@@ -25,11 +27,12 @@ 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++) {
+ unsigned long addr = READ_ONCE_NOCHECK(*state->sp);

- for (state->sp++; state->sp < info->end; state->sp++)
if (__kernel_text_address(addr))
return true;
+ }

state->sp = info->next_sp;

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