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@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20210628113045.045141693@infradead.org

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index bdb0681bece82068634230a13c04af714cf406db..b156e152d6b48d093e4eb1e54290179e0c75743d 100644 (file)
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -316,14 +316,16 @@ static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 }
 
 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++;
        }
 
@@ -562,7 +564,7 @@ static int __jump_label_mod_text_reserved(void *start, void *end)
 
        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);
 
@@ -788,8 +790,9 @@ 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;