[PATCH v14 03/14] kprobes: Protect kprobe_blacklist with RCU

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

__within_kprobe_blacklist() traverses kprobe_blacklist without holding
kprobe_mutex. When a module is unloaded, kprobe_remove_area_blacklist()
removes blacklist entries and immediately frees them with kfree().
A concurrent call to within_kprobe_blacklist() can therefore dereference
freed memory.

Furthermore, within_kprobe_blacklist() can be called in atomic or
non-preemptible contexts where the sleeping kprobe_mutex cannot be taken.

Protect kprobe_blacklist with RCU. Use guard(rcu)() and
list_for_each_entry_rcu() for traversal, list_add_tail_rcu() for
insertions, list_del_rcu() for deletions, and kfree_rcu() to reclaim
entries safely after a grace period.

Assisted-by: Antigravity:gemini-3.7-flash
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v13:
 - Newly added.
---
 include/linux/kprobes.h |    1 +
 kernel/kprobes.c        |   14 ++++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8c4f3bb24429..e6de7ae55bda 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -181,6 +181,7 @@ struct kprobe_blacklist_entry {
 	struct list_head list;
 	unsigned long start_addr;
 	unsigned long end_addr;
+	struct rcu_head rcu;
 };
 
 #ifdef CONFIG_KPROBES
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index bfc89083daa9..6337da5cab9e 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1447,8 +1447,14 @@ static bool __within_kprobe_blacklist(unsigned long addr)
 	/*
 	 * If 'kprobe_blacklist' is defined, check the address and
 	 * reject any probe registration in the prohibited area.
+	 * Note: this can return true during transition period where
+	 * (start_addr, end_addr) in the black list is shrinking
+	 * but old entry has not been removed yet. This is acceptable
+	 * because the worst case is that we reject more probes than
+	 * we should.
 	 */
-	list_for_each_entry(ent, &kprobe_blacklist, list) {
+	guard(rcu)();
+	list_for_each_entry_rcu(ent, &kprobe_blacklist, list) {
 		if (addr >= ent->start_addr && addr < ent->end_addr)
 			return true;
 	}
@@ -2509,7 +2515,7 @@ int kprobe_add_ksym_blacklist(unsigned long entry)
 	ent->start_addr = entry;
 	ent->end_addr = entry + size;
 	INIT_LIST_HEAD(&ent->list);
-	list_add_tail(&ent->list, &kprobe_blacklist);
+	list_add_tail_rcu(&ent->list, &kprobe_blacklist);
 
 	return (int)size;
 }
@@ -2603,8 +2609,8 @@ static void kprobe_remove_area_blacklist(unsigned long start, unsigned long end)
 	list_for_each_entry_safe(ent, n, &kprobe_blacklist, list) {
 		if (ent->start_addr < start || ent->start_addr >= end)
 			continue;
-		list_del(&ent->list);
-		kfree(ent);
+		list_del_rcu(&ent->list);
+		kfree_rcu(ent, rcu);
 	}
 }