linux-kernel - [tip:x86/urgent] x86/unwind: Disable KASAN checking in the ORC unwinder

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Message-ID: <tip-881125bfe65bb772f34f4fcb04a35dfe117e186a@git.kernel.org>
Date:   Wed, 8 Nov 2017 01:46:52 -0800
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     mingo@...nel.org, torvalds@...ux-foundation.org,
        bauerman@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, peterz@...radead.org, hpa@...or.com,
        jpoimboe@...hat.com, fengguang.wu@...el.com
Subject: [tip:x86/urgent] x86/unwind: Disable KASAN checking in the ORC
 unwinder

Commit-ID:  881125bfe65bb772f34f4fcb04a35dfe117e186a
Gitweb:     https://git.kernel.org/tip/881125bfe65bb772f34f4fcb04a35dfe117e186a
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Tue, 7 Nov 2017 20:19:34 -0600
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 8 Nov 2017 10:21:49 +0100

x86/unwind: Disable KASAN checking in the ORC unwinder

Fengguang reported a KASAN warning:

  Kprobe smoke test: started
  ==================================================================
  BUG: KASAN: stack-out-of-bounds in deref_stack_reg+0xb5/0x11a
  Read of size 8 at addr ffff8800001c7cd8 by task swapper/1

  CPU: 0 PID: 1 Comm: swapper Not tainted 4.14.0-rc8 #26
  Call Trace:
   <#DB>
   ...
   save_trace+0xd9/0x1d3
   mark_lock+0x5f7/0xdc3
   __lock_acquire+0x6b4/0x38ef
   lock_acquire+0x1a1/0x2aa
   _raw_spin_lock_irqsave+0x46/0x55
   kretprobe_table_lock+0x1a/0x42
   pre_handler_kretprobe+0x3f5/0x521
   kprobe_int3_handler+0x19c/0x25f
   do_int3+0x61/0x142
   int3+0x30/0x60
  [...]

The ORC unwinder got confused by some kprobes changes, which isn't
surprising since the runtime code no longer matches vmlinux and the
stack was modified for kretprobes.

Until we have a way for generated code to register changes with the
unwinder, these types of warnings are inevitable.  So just disable KASAN
checks for stack accesses in the ORC unwinder.

Reported-by: Fengguang Wu <fengguang.wu@...el.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thiago Jung Bauermann <bauerman@...ux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20171108021934.zbl6unh5hpugybc5@treble
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/unwind_orc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index b95007e..a3f973b 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -279,7 +279,7 @@ static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
 	if (!stack_access_ok(state, addr, sizeof(long)))
 		return false;
 
-	*val = READ_ONCE_TASK_STACK(state->task, *(unsigned long *)addr);
+	*val = READ_ONCE_NOCHECK(*(unsigned long *)addr);
 	return true;
 }