linux-kernel - [PATCH urgent] Revert "x86/unwind: Detect bad stack return address"

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Message-Id: <02f296848fbf49fb72dfeea706413ecbd9d4caf6.1482418739.git.jpoimboe@redhat.com>
Date:   Thu, 22 Dec 2016 09:02:49 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH urgent] Revert "x86/unwind: Detect bad stack return address"

This reverts commit b6959a362177 ("x86/unwind: Detect bad stack return
address").

Andrey Konovalov reported an unwinder warning:

  WARNING: unrecognized kernel stack return address ffffffffa0000001 at ffff88006377fa18 in a.out:4467

The unwind was initiated from an interrupt which occurred while running in the
generated code for a kprobe.  The unwinder printed the warning because it
expected regs->ip to point to a valid text address, but instead it pointed to
the generated code.

Eventually we may want come up with a way to identify generated kprobe
code so the unwinder can know that it's a valid return address.  Until
then, just remove the warning.

Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/unwind_frame.c | 11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 20d4b4e..4443e49 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -51,16 +51,7 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
 	addr = ftrace_graph_ret_addr(state->task, &state->graph_idx, *addr_p,
 				     addr_p);
 
-	if (!__kernel_text_address(addr)) {
-		printk_deferred_once(KERN_WARNING
-			"WARNING: unrecognized kernel stack return address %p at %p in %s:%d\n",
-			(void *)addr, addr_p, state->task->comm,
-			state->task->pid);
-		unwind_dump(state, addr_p);
-		return 0;
-	}
-
-	return addr;
+	return __kernel_text_address(addr) ? addr : 0;
 }
 EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
-- 
2.7.4