linux-kernel - [PATCH v3 2/3] jump_label: Warn on failed jump

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Message-Id: <c0a8f5c22477fb387465ac2ee57aab1d0c35590d.1519002843.git.jpoimboe@redhat.com>
Date:   Sun, 18 Feb 2018 19:17:20 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Jason Baron <jbaron@...mai.com>, Borislav Petkov <bp@...e.de>
Subject: [PATCH v3 2/3] jump_label: Warn on failed jump_label patch

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>
---
 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 3adc3d37623b..250e7e6540cc 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);
+		}
 	}
 }
 
-- 
2.14.3