Re: [PATCH 2/3] [RFC] seccomp: give BPF x32 bit when restoring x32 filter

It includes the X32 bit.

On July 11, 2014 3:52:42 PM PDT, Kees Cook <keescook(a)chromium.org&gt; wrote: >On Fri, Jul 11, 2014 at 3:48 PM, Kees Cook <keescook(a)chromium.org&gt; >wrote: >> On Fri, Jul 11, 2014 at 12:36 PM, Paul Moore <pmoore(a)redhat.com&gt; >wrote: >>> Anyway, getting back to the idea I mentioned earlier ... as many of >you may >>> know, Kees (added to the CC line) is working on some seccomp filter >>> improvements which will result in a new seccomp syscall. Perhaps >one way >>> forward is to preserve everything as it is currently with the >prctl() >>> interface, but with the new seccomp() based interface we fixup x32 >and use the >>> new AUDIT_ARCH_X32 token? It might result in a bit of ugliness in >some of the >>> kernel, but I don't think it would be too bad, and I think it would >address >>> both our concerns. >> >> Adding AUDIT_ARCH_X32: yes please. (On that note, the comment "/* >Both >> x32 and x86_64 are considered "64-bit". */" should be changed...) >> >> Just so I understand: currently x86_64 and x32 both present as >> AUDIT_ARCH_X86_64. The x32 syscalls are seen as in a different range >> (due to the set high bit). >> >> The seccomp used in Chrome, Chrome OS, and vsftpd should all only do >> whitelisting by both arch and syscall, so adding AUDIT_ARCH_X32 >> without setting __X32_SYSCALL_BIT would be totally fine (it would >> catch the arch instead of the syscall). This sounds similar to how >> libseccomp is doing things, so these should be fine. > >I should clarify: seccomp expects to find whatever is sent as the >syscall nr... as in the __NR_read used like this: > > BPF_STMT(BPF_LD+BPF_W+BPF_ABS, > offsetof(struct seccomp_data, nr)), > BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, __NR_read, 0, 1), > BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_KILL), > BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW), > >Are there native x32 users yet? What does __NR_read resolve to via the >uapi on a native x32 userspace? > >-Kees > >> The only project I know of doing blacklisting is lxc, and Eric's >> example looks a lot like a discussion I saw with lxc and init_module. >> :) So it sounds like we can get this right there. >> >> I'd like to avoid carrying a delta on filter logic based on the prctl >> vs syscall entry. Can we find any userspace filters being used that a >> "correct" fix would break? (If so, then yes, we'll need to do this >> proposed "via prctl or via syscall?" change.) >> >> -Kees >> >> -- >> Kees Cook >> Chrome OS Security -- Sent from my mobile phone. Please pardon brevity and lack of formatting.