On Friday, February 15, 2013 11:02:49 AM H. Peter Anvin wrote: > On 02/15/2013 09:21 AM, Paul Moore wrote: > > Commit fca460f95e928bae373daa8295877b6905bc62b8 simplified the x32 > > implementation by creating a syscall bitmask, equal to 0x40000000, that > > could be applied to x32 syscalls such that the masked syscall number > > would be the same as a x86_64 syscall. While that patch was a nice > > way to simplify the code, it went a bit too far by adding the mask to > > syscall_get_nr(); returning the masked syscall numbers can cause > > confusion with callers that expect syscall numbers matching the x32 > > ABI, e.g. unmasked syscall numbers. > > > > This patch fixes this by simply removing the mask from syscall_get_nr() > > while preserving the other changes from the original commit. While > > there are several syscall_get_nr() callers in the kernel, most simply > > check that the syscall number is greater than zero, in this case this > > patch will have no effect. Of those remaining callers, they appear > > to be few, seccomp and ftrace, and from my testing of seccomp without > > this patch the original commit definitely breaks things; the seccomp > > filter does not correctly filter the syscalls due to the difference in > > syscall numbers in the BPF filter and the value from syscall_get_nr(). > > Applying this patch restores the seccomp BPF filter functionality on > > x32. > > > > I've tested this patch with the seccomp BPF filters as well as ftrace > > and everything looks reasonable to me; needless to say general usage > > seemed fine as well. > > Hi... it isn't 100% clear from the description if you have audited *all* > the callers?
I audited all of the syscall_get_nr() callers using the LXR at http://lxr.free-electrons.com with the 3.7 sources. If you exclude all of the architecture dependent stuff that is non-x86 you arrive at the following list of callers: * kernel/seccomp.c:seccomp_bpf_load() This is where I noticed the problem, broken w/o the patch. * lib/syscall.c:collect_syscall()/task_current_syscall() The task_current_syscall() function is really only called by proc_pid_syscall() which displays the syscall number back to the user via a /proc entry, in which case this patch appears to correct a problem similar to what was seen with seccomp. * kernel/trace/trace_syscalls.c:ftrace_syscall_enter() * kernel/trace/trace_syscalls.c:ftrace_syscall_exit() * kernel/trace/trace_syscalls.c:perf_syscall_enter() * kernel/trace/trace_syscalls.c:perf_syscall_exit() The ftrace/perf is the one user that I am least sure about, as noted above, I did some simple tests based on what I could find via Google but a quick review by someone who is more familiar with this code would be appreciated. I'm most concerned about the syscall_metadata bits ... * include/trace/events/syscall.h Another, what I assume, is a ftrace user; I'm assuming the patch is reasonable based on my testing, but once again further review would be appreciated. * arch/x86/kernel/ptrace.c:putreg32() * arch/x86/kernel/signal.c:handle_signal() * arch/x86/kernel/signal.c:do_signal() Simple grater than zero checks. -- paul moore security and virtualization @ redhat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
