Messages in this thread | | | From | Paul Moore <> | Subject | Re: [PATCH 2/3] [RFC] seccomp: give BPF x32 bit when restoring x32 filter | Date | Fri, 11 Jul 2014 12:32:05 -0400 |
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On Friday, July 11, 2014 12:23:33 PM Eric Paris wrote: > On Fri, 2014-07-11 at 12:21 -0400, Paul Moore wrote: > > On Friday, July 11, 2014 12:16:47 PM Eric Paris wrote: > > > On Fri, 2014-07-11 at 12:11 -0400, Paul Moore wrote: > > > > On Thursday, July 10, 2014 09:06:02 PM H. Peter Anvin wrote: > > > > > Incidentally: do seccomp users know that on an x86-64 system you can > > > > > recevie system calls from any of the x86 architectures, regardless > > > > > of > > > > > how the program is invoked? (This is unusual, so normally denying > > > > > those > > > > > "alien" calls is the right thing to do.) > > > > > > > > I obviously can't speak for all seccomp users, but libseccomp handles > > > > this > > > > by checking the seccomp_data->arch value at the start of the filter > > > > and > > > > killing (by default) any non-native architectures. If you want, you > > > > can > > > > change this default behavior or add support for other architectures > > > > (e.g. > > > > create a filter that allows both x86-64 and x32 but disallows x86, or > > > > any > > > > combination of the three for that matter). > > > > > > Maybe libseccomp does some HORRIFIC contortions under the hood, but the > > > interface is crap... Since seccomp_data->arch can't distinguish between > > > X32 and X86_64. If I write a seccomp filter which says > > > > > > KILL arch != x86_64 > > > KILL init_module > > > ALLOW everything else > > > > > > I can still call init_module, I just have to use the X32 variant. > > > > > > If libseccomp is translating: > > > > > > KILL arch != x86_64 into: > > > > > > KILL arch != x86_64 > > > KILL syscall_nr >= 2000 > > > > > > That's just showing how dumb the kernel interface is... Good for you > > > guys, but the kernel is just being dumb :) > > > > You're not going to hear me ever say that I like how the x32 ABI was done, > > it is a real mess from a seccomp filter point of view and we have to do > > some nasty stuff in libseccomp to make it all work correctly (see my > > comments on the libseccomp-devel list regarding my severe displeasure > > over x32), but what's done is done. > > > > I think it's too late to change the x32 seccomp filter ABI. > > So we have a security interface that is damn near impossible to get > right. Perfect.
What? Having to do two comparisons instead of one is "damn near impossible"? I think that might be a bit of an overreaction don't you think?
> I think this explains exactly why I support this idea. Make X32 look > like everyone else ...
You do realize that this patch set makes x32 the odd man out by having syscall_get_nr() return a different syscall number than what was used to make the syscall? I don't understand how that makes "x32 look like everyone else".
> ... and put these custom horrific hacks in seccomp if we are unwilling to > 'do it right'
If you want to add the new x32 audit arch #define, go for it, like I said that was something that I feel should have been in there from the beginning. As far as I'm concerned you can even put a hack in kernel/seccomp.c to rewrite the arch token value if it makes your life easier.
> Honestly, how many people are using seccomp on X32 and would be horribly > pissed if we just fixed it?
Okay, please stop suggesting we break the x32 kernel/user interface to workaround a flaw in audit. I get that it sucks for audit, I really do, but this is audit's problem.
-- paul moore security and virtualization @ redhat
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