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

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