> On May 18, 2022, at 10:09 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Sun, May 15, 2022 at 10:40:48PM -0700, Song Liu wrote: >> Introduce a memset like API for text_poke. This will be used to fill the >> unused RX memory with illegal instructions. > > FWIW, you're going to use it to set INT3 (0xCC), that's not an illegal > instruction. INTO (0xCE) would be an illegal instruction (in 64bit > mode). Hmm… we have been using INT3 as illegal/invalid/special instructions in the JIT. I guess they are equally good for this job? > > >> + return addr; >> +} >> + >> +/** >> + * text_poke_set - memset into (an unused part of) RX memory >> + * @addr: address to modify >> + * @c: the byte to fill the area with >> + * @len: length to copy, could be more than 2x PAGE_SIZE >> + * >> + * Not safe against concurrent execution; useful for JITs to dump >> + * new code blocks into unused regions of RX memory. Can be used in >> + * conjunction with synchronize_rcu_tasks() to wait for existing >> + * execution to quiesce after having made sure no existing functions >> + * pointers are live. > > That comment suffers from copy-pasta and needs an update because it > clearly isn't correct. Will fix in the next version. > >> + */ > > Other than that, seems fine. > > Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Thanks, Song
