Re: [PATCH 1/3] jump_label: Fix jump_label_text_reserved() vs __init

[Masami Hiramatsu <mhiramat@kernel.org>]

On Mon, 28 Jun 2021 13:24:10 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> 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>

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Thank you,

> ---
>  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;
> 
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>