Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions

[Naveen N. Rao]

Peter Zijlstra wrote:
> On Tue, Mar 01, 2022 at 11:49:05AM +0900, Masami Hiramatsu wrote:
>
> > - the 'offset' is NOT limited under the symbol size.
> >   (e.g. symbol_name = "_text" and @offset points the offset of target symbol from _text)
> >
> > This means we need to call kallsyms_lookup_size_offset() in this case too.
>
> I'm feeling we should error out in that case. Using sym+offset beyond
> the limits of sym is just daft.
>
> But if you really want/need to retain that, then yes, we need that
> else branch unconditionally :/

I think we will need this. perf always specifies an offset from _text.

Also, I just noticed:

> -static kprobe_opcode_t *_kprobe_addr(kprobe_opcode_t *addr,
> -			const char *symbol_name, unsigned int offset)
> +static kprobe_opcode_t *
> +_kprobe_addr(kprobe_opcode_t *addr, const char *symbol_name,
> +	     unsigned long offset, bool *on_func_entry)
>  {
>  	if ((symbol_name && addr) || (!symbol_name && !addr))
>  		goto invalid;
>  
>  	if (symbol_name) {
> +		/*
> +		 * Input: @sym + @offset
> +		 * Output: @addr + @offset
> +		 *
> +		 * NOTE: kprobe_lookup_name() does *NOT* fold the offset
> +		 *       argument into it's output!
> +		 */
>  		addr = kprobe_lookup_name(symbol_name, offset);
>  		if (!addr)
>  			return ERR_PTR(-ENOENT);
> +	} else {
> +		/*
> +		 * Input: @addr + @offset
> +		 * Output: @addr' + @offset'
> +		 */
> +		if (!kallsyms_lookup_size_offset((unsigned long)addr + offset,
> +						 NULL, &offset))
> +			return ERR_PTR(-ENOENT);
> +		addr = (kprobe_opcode_t *)((unsigned long)addr - offset);
>  	}

This looks wrong. I think you need to retain offset to calculate the 
proper function entry address so that you can do:
	addr = (kprobe_opcode_t *)((unsigned long)(addr + offset) - func_offset);
	offset = func_offset;

>  
> -	addr = (kprobe_opcode_t *)(((char *)addr) + offset);
> +	addr = arch_adjust_kprobe_addr((unsigned long)addr, offset, on_func_entry);
>  	if (addr)
>  		return addr;

- Naveen