Subject: Re: [PATCH][v2] uprobes/x86: emulate push insns for uprobe on x86

From: Oleg Nesterov <[email-masked]>
Date: Tue, 14 Nov 2017 16:34:24 +0100

On 11/13, Yonghong Song wrote:
>
> On 11/13/17 4:59 AM, Oleg Nesterov wrote:
> >>+		switch (opc1) {
> >>+		case 0x50:
> >>+			reg_offset = offsetof(struct pt_regs, r8);
> >>+			break;
> >>+		case 0x51:
> >>+			reg_offset = offsetof(struct pt_regs, r9);
> >>+			break;
> >>+		case 0x52:
> >>+			reg_offset = offsetof(struct pt_regs, r10);
> >>+			break;
> >>+		case 0x53:
> >>+			reg_offset = offsetof(struct pt_regs, r11);
> >>+			break;
> >>+		case 0x54:
> >>+			reg_offset = offsetof(struct pt_regs, r12);
> >>+			break;
> >>+		case 0x55:
> >>+			reg_offset = offsetof(struct pt_regs, r13);
> >>+			break;
> >>+		case 0x56:
> >>+			reg_offset = offsetof(struct pt_regs, r14);
> >>+			break;
> >>+		case 0x57:
> >>+			reg_offset = offsetof(struct pt_regs, r15);
> >>+			break;
> >>+		}
> >>+#else
> >>+		return -ENOSYS;
> >>+#endif
> >
> >OK, but shouldn't we also return ENOSYS if CONFIG_X86_64=y but the probed task is 32bit?
>
> Just tested with a 32bit app on x86 box and segfaults.

Hmm. How did you verify this?

Your v3 doesn't look right and it seems you misunderstood me...

> Yes, we would need to
> return ENOSYS if the app is 32bit on 64bit system.

Only if insn->length == 2. "push bp" and other valid 32bit push'es should be
emulated correctly or your patch is wrong. Confused...

> >Or in this case uprobe_init_insn(x86_64 => false) should fail and push_setup_xol_ops()
> >won't be called?

So it doesn't fail?

Oleg.