linux-kernel - [PATCH 1/3] jump_label: Fix jump_label_text_reserved() vs _

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Message-ID: <20210628113045.045141693@infradead.org>
Date:   Mon, 28 Jun 2021 13:24:10 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     jpoimboe@...hat.com, jbaron@...mai.com, rostedt@...dmis.org,
        ardb@...nel.org, naveen.n.rao@...ux.ibm.com,
        anil.s.keshavamurthy@...el.com, mhiramat@...nel.org,
        davem@...emloft.net
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        kernel test robot <oliver.sang@...el.com>
Subject: [PATCH 1/3] jump_label: Fix jump_label_text_reserved() vs __init

It turns out that jump_label_text_reserved() was reporting __init text
as being reserved past the time when the __init text was freed and
re-used.

For a long time, this resulted in, at worst, not being able to kprobe
text that happened to land at the re-used address. However a recent
commit e7bf1ba97afd ("jump_label, x86: Emit short JMP") made it a
fatal mistake because it now needs to read the instruction in order to
determine the conflict -- an instruction that's no longer there.

Fixes: 4c3ef6d79328 ("jump label: Add jump_label_text_reserved() to reserve jump points")
Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/jump_label.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -316,14 +316,16 @@ static int addr_conflict(struct jump_ent
 }
 
 static int __jump_label_text_reserved(struct jump_entry *iter_start,
-		struct jump_entry *iter_stop, void *start, void *end)
+		struct jump_entry *iter_stop, void *start, void *end, bool init)
 {
 	struct jump_entry *iter;
 
 	iter = iter_start;
 	while (iter < iter_stop) {
-		if (addr_conflict(iter, start, end))
-			return 1;
+		if (init || !jump_entry_is_init(iter)) {
+			if (addr_conflict(iter, start, end))
+				return 1;
+		}
 		iter++;
 	}
 
@@ -561,7 +563,7 @@ static int __jump_label_mod_text_reserve
 
 	ret = __jump_label_text_reserved(mod->jump_entries,
 				mod->jump_entries + mod->num_jump_entries,
-				start, end);
+				start, end, mod->state == MODULE_STATE_COMING);
 
 	module_put(mod);
 
@@ -786,8 +788,9 @@ early_initcall(jump_label_init_module);
  */
 int jump_label_text_reserved(void *start, void *end)
 {
+	bool init = system_state < SYSTEM_RUNNING;
 	int ret = __jump_label_text_reserved(__start___jump_table,
-			__stop___jump_table, start, end);
+			__stop___jump_table, start, end, init);
 
 	if (ret)
 		return ret;