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

[Yonghong Song]

On 11/14/17 7:34 AM, Oleg Nesterov wrote:
> 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?

On a x86_32 box, I compiled the test case with static libraries 
(including static libc). And I then run this binary on x86_64 with
uprobe enabled. You will need to install glibc-static package to make it 
work.

> 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.