On Fri, Sep 25, 2020 at 2:18 AM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, Sep 25, 2020 at 02:15:50AM +0200, Jann Horn wrote: > > On Fri, Sep 25, 2020 at 2:01 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > > 2) seccomp needs to handle "multiplexed" tables like x86_x32 (distros > > > haven't removed CONFIG_X86_X32 widely yet, so it is a reality that > > > it must be dealt with), which means seccomp's idea of the arch > > > "number" can't be the same as the AUDIT_ARCH. > > > > Sure, distros ship it; but basically nobody uses it, it doesn't have > > to be fast. As long as we don't *break* it, everything's fine. And if > > we ignore the existence of X32 in the fastpath, that'll just mean that > > syscalls with the X32 marker bit always hit the seccomp slowpath > > (because it'll look like the syscall number is out-of-bounds ) - no > > problem. > > You do realize that X32 is amd64 counterpart of mips n32, right? And that's > not "basically nobody uses it"... What makes X32 weird for seccomp is that it has the syscall tables for X86-64 and X32 mushed together, using the single architecture identifier AUDIT_ARCH_X86_64. I believe that's what Kees referred to by "multiplexed tables". As far as I can tell, MIPS is more well-behaved there and uses the separate architecture identifiers AUDIT_ARCH_MIPS|__AUDIT_ARCH_64BIT and AUDIT_ARCH_MIPS|__AUDIT_ARCH_64BIT|__AUDIT_ARCH_CONVENTION_MIPS64_N32. (But no, I did not actually realize that that's what N32 is. Thanks for the explanation, I was wondering why MIPS was the only architecture with three architecture identifiers...)
