Re: [PATCH 5.10/5.15 1/1] kprobes: Fix to handle forcibly unoptimized kprobes on freeing_list

[Greg KH]

On Mon, Jan 22, 2024 at 02:30:31PM +0300, Fedor Pchelkin wrote:
> From: "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx>
> 
> commit 4fbd2f83fda0ca44a2ec6421ca3508b355b31858 upstream.
> 
> Since forcibly unoptimized kprobes will be put on the freeing_list directly
> in the unoptimize_kprobe(), do_unoptimize_kprobes() must continue to check
> the freeing_list even if unoptimizing_list is empty.
> 
> This bug can happen if a kprobe is put in an instruction which is in the
> middle of the jump-replaced instruction sequence of an optprobe, *and* the
> optprobe is recently unregistered and queued on unoptimizing_list.
> In this case, the optprobe will be unoptimized forcibly (means immediately)
> and put it into the freeing_list, expecting the optprobe will be handled in
> do_unoptimize_kprobe().
> But if there is no other optprobes on the unoptimizing_list, current code
> returns from the do_unoptimize_kprobe() soon and does not handle the
> optprobe which is on the freeing_list. Then the optprobe will hit the
> WARN_ON_ONCE() in the do_free_cleaned_kprobes(), because it is not handled
> in the latter loop of the do_unoptimize_kprobe().
> 
> To solve this issue, do not return from do_unoptimize_kprobes() immediately
> even if unoptimizing_list is empty.
> 
> Moreover, this change affects another case. kill_optimized_kprobes() expects
> kprobe_optimizer() will just free the optprobe on freeing_list.
> So I changed it to just do list_move() to freeing_list if optprobes are on
> unoptimizing list. And the do_unoptimize_kprobe() will skip
> arch_disarm_kprobe() if the probe on freeing_list has gone flag.
> 
> Link: https://lore.kernel.org/all/Y8URdIfVr3pq2X8w@xxxxxxxxxxxxxxxx/
> Link: https://lore.kernel.org/all/167448024501.3253718.13037333683110512967.stgit@devnote3/
> 
> Fixes: e4add247789e ("kprobes: Fix optimize_kprobe()/unoptimize_kprobe() cancellation logic")
> Reported-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> [fp: adjust comment conflict regarding commit 223a76b268c9 ("kprobes: Fix
>  coding style issues")]
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>
> ---
>  kernel/kprobes.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)

Now queued up, thanks.

greg k-h