Segher Boessenkool <seg...@kernel.crashing.org> writes: > On Thu, Feb 07, 2019 at 10:53:13PM +1100, Michael Ellerman wrote: >> Chandan reported that fstests' generic/026 test hit a crash: > >> The instruction dump decodes as: >> subfic r6,r5,8 >> rlwinm r6,r6,3,0,28 >> ldbrx r9,0,r3 >> ldbrx r10,0,r4 <- >> >> Which shows us doing an 8 byte load from c00000062ac3fff9, which >> crosses the page boundary at c00000062ac40000 and faults. >> >> It's not OK for memcmp to read past the end of the source or >> destination buffers. > > It's not okay to access memory pages unsolicited. Reading past the end > is fine per se.
Yeah I guess that's true. Things like KASAN/valgrind probably disagree, but KASAN at least overrides memcmp AIUI. I guess I feel better about it not reading past the end of the buffers, but maybe I'm being paranoid. The other complication is we support multiple page sizes, so detecting a page boundary is more complicated than it could be. So I guess I'm inclined to stick with this approach, but I can update the change log. cheers
