Re: [PATCH v2] x86/kprobe: Fix crash when probe cs call

[Jinke Han <jinkehan@didiglobal.com>]

> Thanks for fixing! I have just one comment here;

> [...]
 
> > @@ -2180,8 +2181,14 @@ int3_exception_notify(struct notifier_block *self, unsigned long val, void *data
> >  
> >  	if (regs->ip - INT3_INSN_SIZE != selftest)
> >  		return NOTIFY_DONE;
> > -
> > -	int3_emulate_call(regs, (unsigned long)&int3_selftest_callee);
> > +	/*
> > +	 * As seen in int3_selftest_asm, the effective return address
> > +	 * should be placed immediately after the instruction sequence
> > +	 * [int3; nop; nop; nop; nop.]. Therefore, CALL_INSN_SIZE works
> > +	 * perfectly well here.

> Nit: This explanation is somewhat wrong. alternatives only support 5-byte
> call. The TEXT_POKE_MAX_OPCODE_SIZE is 5. When len == 6, alternative.c
> explicitly reserves this only for 0x0f prefixed Jcc.d32

> See alternative.c 
> > /*
> >  * NOTE: crazy scheme to allow patching Jcc.d32 but not increase the size of
> >  * this thing. When len == 6 everything is prefixed with 0x0f and we map
>  * opcode to Jcc.d8, using len to distinguish.
> >  */

> So we don't need to take care of 6 bytes call here.

Thanks for the correction! I'll fix it in v3 soon.
--
Jinke Han

> Others looks good to me.

> Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

> BTW, can this be picked via tip tree ? or I can pick it.

> Thank you,

> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>