On Wed, Feb 22, 2012 at 3:38 PM, Andrew Lutomirski <luto@xxxxxxx> wrote: > On Wed, Feb 22, 2012 at 11:48 AM, Will Drewry <wad@xxxxxxxxxxxx> wrote: >> On Wed, Feb 22, 2012 at 2:34 AM, Indan Zupancic <indan@xxxxxx> wrote: >>> On Tue, February 21, 2012 18:30, Will Drewry wrote: >>>> This change enables SIGSYS, defines _sigfields._sigsys, and adds >>>> x86 (compat) arch support. _sigsys defines fields which allow >>>> a signal handler to receive the triggering system call number, >>>> the relevant AUDIT_ARCH_* value for that number, and the address >>>> of the callsite. >>>> >>>> To ensure that SIGSYS delivery occurs on return from the triggering >>>> system call, SIGSYS is added to the SYNCHRONOUS_MASK macro. I'm >>>> this is enough to ensure it will be synchronous or if it is explicitly >>>> required to ensure an immediate delivery of the signal upon return from >>>> the blocked system call. >>>> >>>> The first consumer of SIGSYS would be seccomp filter. In particular, >>>> a filter program could specify a new return value, SECCOMP_RET_TRAP, >>>> which would result in the system call being denied and the calling >>>> thread signaled. This also means that implementing arch-specific >>>> support can be dependent upon HAVE_ARCH_SECCOMP_FILTER. >>> >>> I think others said this is useful, but I don't see how. Easier >>> debugging compared to checking return values? >>> >>> I suppose SIGSYS can be blocked, so there is no guarantee the process >>> will be killed. >> >> Yeah, this allows for in-process system call emulation, if desired, or >> for the process to dump core/etc. With RET_ERRNO or RET_KILL, there >> isn't any feedback to the system about the state of the process. Kill >> populates audit_seccomp and dmesg, but if the application >> user/developer isn't the system admin, installing audit bits or >> checking system logs seems onerous. > > [Warning: this suggestion may be bad for any number of reasons] > > I wonder if it would be helpful to change the semantics of RET_KILL > slightly. Rather than killing via do_exit, what if it killed via a > forcibly-fatal SIGSYS? That way, the parent's waitid() / SIGCHLD > would indicate CLD_KILLED with si_status == SIGSYS. The parent could > check that and report that the child was probably compromised. > > --Andy I'd prefer sticking with do_exit. This provides much less chance of things going wrong. A parent seeing a child killed with SIGKILL is already pretty distinct, IMO. -Kees -- Kees Cook ChromeOS Security -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
