linux-kernel - [PATCH 4.19 41/48] x86/unwind/orc: Prevent unwinding before ORC initialization

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Date:   Wed, 13 May 2020 11:45:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Miroslav Benes <mbenes@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andy Lutomirski <luto@...nel.org>, Dave Jones <dsj@...com>,
        Jann Horn <jannh@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vince Weaver <vincent.weaver@...ne.edu>
Subject: [PATCH 4.19 41/48] x86/unwind/orc: Prevent unwinding before ORC initialization

From: Josh Poimboeuf <jpoimboe@...hat.com>

commit 98d0c8ebf77e0ba7c54a9ae05ea588f0e9e3f46e upstream.

If the unwinder is called before the ORC data has been initialized,
orc_find() returns NULL, and it tries to fall back to using frame
pointers.  This can cause some unexpected warnings during boot.

Move the 'orc_init' check from orc_find() to __unwind_init(), so that it
doesn't even try to unwind from an uninitialized state.

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Reviewed-by: Miroslav Benes <mbenes@...e.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Jones <dsj@...com>
Cc: Jann Horn <jannh@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vince Weaver <vincent.weaver@...ne.edu>
Link: https://lore.kernel.org/r/069d1499ad606d85532eb32ce39b2441679667d5.1587808742.git.jpoimboe@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/kernel/unwind_orc.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -131,9 +131,6 @@ static struct orc_entry *orc_find(unsign
 {
 	static struct orc_entry *orc;
 
-	if (!orc_init)
-		return NULL;
-
 	if (ip == 0)
 		return &null_orc_entry;
 
@@ -563,6 +560,9 @@ EXPORT_SYMBOL_GPL(unwind_next_frame);
 void __unwind_start(struct unwind_state *state, struct task_struct *task,
 		    struct pt_regs *regs, unsigned long *first_frame)
 {
+	if (!orc_init)
+		goto done;
+
 	memset(state, 0, sizeof(*state));
 	state->task = task;