On 11/24/19 10:52 AM, Pavel Begunkov wrote: > On 24/11/2019 20:10, Jens Axboe wrote: >> On 11/24/19 1:58 AM, Pavel Begunkov wrote: >>> Read/write requests to devices without implemented read/write_iter >>> using fixed buffers causes general protection fault, which totally >>> hangs a machine. >>> >>> io_import_fixed() initialises iov_iter with bvec, but loop_rw_iter() >>> accesses it as iovec, so dereferencing random address. >>> >>> kmap() page by page in this case >> >> This looks good to me, much cleaner/simpler. I've added a few pipe fixed >> buffer tests to liburing as well. Didn't crash for me, but obvious >> garbage coming out. I've flagged this for stable as well. >> > The problem I have is that __user pointer is meant to be checked > for not being a kernel address. I suspect, it could fail in some > device, which double checks the pointer after vfs (e.g. using access_ok()). > Am I wrong? Not a fault at least... > > #define access_ok(...) __range_not_ok(addr, user_addr_max()); They are user pages! So this should be totally fine. The only difference is that we have them pre-mapped. But it's not like we're pretending these kernel pages are user pages, and hence access_ok() should be totally happy with them. > BTW, is there anybody testing it for non x86-64 arch? Would be nice, I've mostly failed at getting other archs interested enough to actually make hardware available. Which seems pretty lame, but only so much I can do there. There _shouldn't_ be anything arch specific, but it would be great to have archs with eg weaker ordering as part of the regular test arsenal. -- Jens Axboe
