linux-kernel - [tip:x86/pti] jump_label: Warn on failed jump

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Message-ID: <tip-5400c00440061515c5bda299c19b6e86b81be798@git.kernel.org>
Date:   Wed, 21 Feb 2018 02:49:00 -0800
From:   tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
        tglx@...utronix.de, jbaron@...mai.com, rostedt@...dmis.org,
        mingo@...nel.org, peterz@...radead.org, hpa@...or.com, bp@...e.de,
        jpoimboe@...hat.com
Subject: [tip:x86/pti] jump_label: Warn on failed jump_label patching
 attempt

Commit-ID:  5400c00440061515c5bda299c19b6e86b81be798
Gitweb:     https://git.kernel.org/tip/5400c00440061515c5bda299c19b6e86b81be798
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Tue, 20 Feb 2018 11:37:52 -0600
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 21 Feb 2018 10:11:39 +0100

jump_label: Warn on failed jump_label patching attempt

Currently when the jump label code encounters an address which isn't
recognized by kernel_text_address(), it just silently fails.

This can be dangerous because jump labels are used in a variety of
places, and are generally expected to work.  Convert the silent failure
to a warning.

This won't warn about attempted writes to tracepoints in __init code
after initmem has been freed, as those are already guarded by the
entry->code check.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...e.de>
Cc: Jason Baron <jbaron@...mai.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/de3a271c93807adb7ed48f4e946b4f9156617680.1519051220.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/jump_label.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index b717765..b2f0b47 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -367,12 +367,15 @@ static void __jump_label_update(struct static_key *key,
 {
 	for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
 		/*
-		 * entry->code set to 0 invalidates module init text sections
-		 * kernel_text_address() verifies we are not in core kernel
-		 * init code, see jump_label_invalidate_module_init().
+		 * An entry->code of 0 indicates an entry which has been
+		 * disabled because it was in an init text area.
 		 */
-		if (entry->code && kernel_text_address(entry->code))
-			arch_jump_label_transform(entry, jump_label_type(entry));
+		if (entry->code) {
+			if (kernel_text_address(entry->code))
+				arch_jump_label_transform(entry, jump_label_type(entry));
+			else
+				WARN_ONCE(1, "can't patch jump_label at %pS", (void *)entry->code);
+		}
 	}
 }