Re: [PATCH][v3] uprobes/x86: emulate push insns for uprobe on x86

On 11/14/17 8:03 AM, Oleg Nesterov wrote:

On 11/14, Oleg Nesterov wrote:

quoted

quoted

+#ifdef CONFIG_X86_64
+	if (test_thread_flag(TIF_ADDR32))
+		return -ENOSYS;
+#endif

No, this doesn't look right, see my previous email. You should do this
check in the "if (insn->length == 2)" branch below, "push bp" should be
emulated correctly.

And test_thread_flag(TIF_ADDR32) is not right too. The caller is not
necessarily the probed task. See is_64bit_mm(mm) in arch_uprobe_analyze_insn().

And again... please check if uprobe_init_insn() fails or not in this case
(32bit task does, say, "push r8"). If it fails, your V2 should be fine.


To remind, uprobes && 32-bit is broken, let me quote my another email:

	The 3rd bug means that you simply can't uprobe a 32bit task on a 64bit
	system, the in_compat_syscall() logic in get_unmapped_area() looks very
	wrong although I need to re-check.

Yes,

quoted

I didn't have time for this problem so far. But emulation should work, so
you can hopefully test your patch.

Ah, no, sizeof_long() is broken by the same reason, so you can't test it...

Right. I hacked the emulate_push_stack (original name: push_ret_address) 
with sizeof_long = 4, and 32bit binary uprobe works fine on x86_64 
platform then... But that will involve a bigger change to propogate
the is_64bit_mm() along the call graph.

OK, I'll try to do something tomorrow, then we will see what can we do
with your patch...

Thanks for reviewing! I will wait for your further comments/direction
before next step.

But it would be nice if you can check what uprobe_init_insn() does in this
case, see above.

As mentioned in my previous email, for 32bit application,
compiler won't generate "push %r8" as "%r8" is only available on
x86_64 platform. For 32bit app, I see "push %bp" etc which does not
have rex_prefix. They cannot be emulated right now due to 
emulate_push_stack needs change.

Oleg.