Hi Kees, I'm struggling to see the bug in the current code, so apologies if my questions aren't helpful.
On Wed, Jun 18, 2014 at 09:27:48PM +0100, Kees Cook wrote: > An x86 tracer wanting to change the syscall uses PTRACE_SETREGS > (stored to regs->orig_ax), and an ARM tracer uses PTRACE_SET_SYSCALL > (stored to current_thread_info()->syscall). When this happens, the > syscall can change across the call to secure_computing(), since it may > block on tracer notification, and the tracer can then make changes > to the process, before we return from secure_computing(). This > means the code must respect the changed syscall after the > secure_computing() call in syscall_trace_enter(). The same is true > for tracehook_report_syscall_entry() which may also block and change > the syscall. I don't think I understand what you mean by `the code must respect the changed syscall'. The current code does indeed issue the new syscall, so are you more concerned with secure_computing changing ->syscall, then the debugger can't see the new syscall when it sees the trap from tracehook? Are these even supposed to inter-operate? > The x86 code handles this (it expects orig_ax to always be the > desired syscall). In the ARM case, this means we should not be touching > current_thread_info()->syscall after its initial assignment. All failures > should result in a -1 syscall, though. The only time we explicitly touch ->syscall is when we're aborting the call (i.e. writing -1), which I think is fine. Will -- 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/
