release/5.2.43/x86-unwind-orc-Fix-error-handling-in-__unwind_start.patch

From bb1473ad47c809331691da42a23b884130e7922d Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Thu, 14 May 2020 15:31:10 -0500
Subject: [PATCH] x86/unwind/orc: Fix error handling in __unwind_start()

commit 71c95825289f585014fe9741b051d32a7a916680 upstream.

The unwind_state 'error' field is used to inform the reliable unwinding
code that the stack trace can't be trusted.  Set this field for all
errors in __unwind_start().

Also, move the zeroing out of the unwind_state struct to before the ORC
table initialization check, to prevent the caller from reading
uninitialized data if the ORC table is corrupted.

Fixes: af085d9084b4 ("stacktrace/x86: add function for detecting reliable stack traces")
Fixes: d3a09104018c ("x86/unwinder/orc: Dont bail on stack overflow")
Fixes: 98d0c8ebf77e ("x86/unwind/orc: Prevent unwinding before ORC initialization")
Reported-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d6ac7215a84ca92b895fdd2e1aa546729417e6e6.1589487277.git.jpoimboe@redhat.com
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index fb37221a1532..647e6af0883d 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -608,23 +608,23 @@ 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;
 
+	if (!orc_init)
+		goto err;
+
 	/*
 	 * Refuse to unwind the stack of a task while it's executing on another
 	 * CPU.  This check is racy, but that's ok: the unwinder has other
 	 * checks to prevent it from going off the rails.
 	 */
 	if (task_on_another_cpu(task))
-		goto done;
+		goto err;
 
 	if (regs) {
 		if (user_mode(regs))
-			goto done;
+			goto the_end;
 
 		state->ip = regs->ip;
 		state->sp = regs->sp;
@@ -657,6 +657,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 		 * generate some kind of backtrace if this happens.
 		 */
 		void *next_page = (void *)PAGE_ALIGN((unsigned long)state->sp);
+		state->error = true;
 		if (get_stack_info(next_page, state->task, &state->stack_info,
 				   &state->stack_mask))
 			return;
@@ -682,8 +683,9 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 
 	return;
 
-done:
+err:
+	state->error = true;
+the_end:
 	state->stack_info.type = STACK_TYPE_UNKNOWN;
-	return;
 }
 EXPORT_SYMBOL_GPL(__unwind_start);
-- 
2.7.4