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?
I'm not sure what portion of my code you mentioned as "completely different", but
1) setting x0 to -ENOSYS is necessary because, otherwise, user-issued syscall(-1) will return a bogus value when audit tracing is on.
Please note that, on arm, not traced traced ------ ------ syscall(-1) aborted OOPs(BUG_ON) syscall(-3000) aborted aborted syscall(1000) ENOSYS ENOSYS
So, anyhow, its a bit difficult and meaningless to mimic these invalid cases.
2) branching a new label, syscall_trace_return_skip (see entry.S), after syscall_trace_enter() is necessary in order to avoid OOPS in audit_syscall_enter() as we discussed.
Did I make it clear?
-Takahiro AKASHI
Will