From: Dmitry Vyukov > Sent: 16 January 2017 14:04 > >> >> I've enabled CONFIG_HARDENED_USERCOPY_PAGESPAN on syzkaller fuzzer and ... > >> The code also takes into account compound pages. As far as I > >> understand the intention of the check is to effectively find > >> out-of-bounds copies (e.g. goes beyond the current heap allocation). I > >> would expect that stacks are allocated as compound pages and don't > >> trigger this check. I don't see it is firing in other similar places. > >> > > Honestly, I'm not overly familiar with stack page allocation, at least not so > > far as compound vs. single page allocation is concerned. I suppose the question > > your really asking here is: Have you found a case in which the syscall fuzzer > > has forced the allocation of an insecure non-compound page on the stack, or is > > this a false positive warning. I can't provide the answer to that. > > Yes. I added Kees, author of CONFIG_HARDENED_USERCOPY_PAGESPAN, to To line. > Kees, is this a false positive? I'd guess that the kernel stack is (somehow) allocated page by page rather than by a single multi-page allocate. Or maybe vmalloc() isn't setting the required flag?? David ��.n��������+%������w��{.n�����{������ܨ}���Ơz�j:+v�����w����ޙ��&�)ߡ�a����z�ޗ���ݢj��w�f