Will,
When I was looking into syscall_trace_exit() more closely, I found another (big) problem. There are two system calls, execve() and rt_sigreturn(), which change 'syscallno' in pt_regs to -1 in start_thread() and restore_sigframe(), respectively.
Since syscallno is not valid anymore in syscall_trace_exit() for these system calls, we cannot create a correct syscall exit record for tracepoint in trace_sys_exit() (=> ftrace_syscall_exit()) and for audit in audit_syscall_exit().
This does not happen on arm because syscall numbers are kept in thread_info on arm.
How can we deal with this issue?
-Takahiro AKASHI
On 08/27/2014 02:51 AM, Will Deacon wrote:
On Fri, Aug 22, 2014 at 01:35:17AM +0100, AKASHI Takahiro wrote:
On 08/22/2014 02:08 AM, Kees Cook wrote:
On Thu, Aug 21, 2014 at 3:56 AM, AKASHI Takahiro takahiro.akashi@linaro.org wrote:
diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 8876049..c54dbcc 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -1121,9 +1121,29 @@ static void tracehook_report_syscall(struct pt_regs *regs,
asmlinkage int syscall_trace_enter(struct pt_regs *regs) {
unsigned int saved_syscallno = regs->syscallno;if (test_thread_flag(TIF_SYSCALL_TRACE)) tracehook_report_syscall(regs, PTRACE_SYSCALL_ENTER);if (IS_SKIP_SYSCALL(regs->syscallno)) {/** RESTRICTION: we can't modify a return value of user* issued syscall(-1) here. In order to ease this flavor,* we need to treat whatever value in x0 as a return value,* but this might result in a bogus value being returned.*//** NOTE: syscallno may also be set to -1 if fatal signal is* detected in tracehook_report_syscall_entry(), but since* a value set to x0 here is not used in this case, we may* neglect the case.*/if (!test_thread_flag(TIF_SYSCALL_TRACE) ||(IS_SKIP_SYSCALL(saved_syscallno)))regs->regs[0] = -ENOSYS;}I don't have a runtime environment yet for arm64, so I can't test this directly myself, so I'm just trying to eyeball this. :)
Once the seccomp logic is added here, I don't think using -2 as a special value will work. Doesn't this mean the Oops is possible by the user issuing a "-2" syscall? As in, if TIF_SYSCALL_WORK is set, and the user passed -2 as the syscall, audit will be called only on entry, and then skipped on exit?
Oops, you're absolutely right. I didn't think of this case. syscall_trace_enter() should not return a syscallno directly, but always return -1 if syscallno < 0. (except when secure_computing() returns with -1) This also implies that tracehook_report_syscall() should also have a return value.
Will, is this fine with you?
Well, the first thing that jumps out at me is why this is being done completely differently for arm64 and arm. I thought adding the new ptrace requests would reconcile the differences?
Will