Re: [PATCH v9 02/15] livepatch: use `-z unique-symbol` if available to nuke pos-based search

[Miroslav Benes <mbenes@suse.cz>]

> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -143,11 +143,13 @@ static int klp_find_callback(void *data, const char *name,
>  	args->count++;
>  
>  	/*
> -	 * Finish the search when the symbol is found for the desired position
> -	 * or the position is not defined for a non-unique symbol.
> +	 * Finish the search when unique symbol names are enabled
> +	 * or the symbol is found for the desired position or the
> +	 * position is not defined for a non-unique symbol.
>  	 */
> -	if ((args->pos && (args->count == args->pos)) ||
> -	    (!args->pos && (args->count > 1)))
> +	if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL) ||
> +	    (args->pos && args->count == args->pos) ||
> +	    (!args->pos && args->count > 1))
>  		return 1;
>  
>  	return 0;
> @@ -171,17 +173,21 @@ static int klp_find_object_symbol(const char *objname, const char *name,
>  
>  	/*
>  	 * Ensure an address was found. If sympos is 0, ensure symbol is unique;
> -	 * otherwise ensure the symbol position count matches sympos.
> +	 * otherwise ensure the symbol position count matches sympos. If the LD
> +	 * `-z unique` flag is enabled, sympos checks are not relevant.
>  	 */
> -	if (args.addr == 0)
> +	if (args.addr == 0) {
>  		pr_err("symbol '%s' not found in symbol table\n", name);
> -	else if (args.count > 1 && sympos == 0) {
> +	} else if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL)) {
> +		goto out_ok;
> +	} else if (args.count > 1 && sympos == 0) {
>  		pr_err("unresolvable ambiguity for symbol '%s' in object '%s'\n",
>  		       name, objname);
>  	} else if (sympos != args.count && sympos > 0) {
>  		pr_err("symbol position %lu for symbol '%s' in object '%s' not found\n",
>  		       sympos, name, objname ? objname : "vmlinux");
>  	} else {
> +out_ok:
>  		*addr = args.addr;
>  		return 0;
>  	}

I think it would be better to return to something like

if (IS_ENABLED(CONFIG_LD_HAS_Z_UNIQUE_SYMBOL))
        sympos = 0;

in klp_find_object_symbol() just after kallsyms search is performed.

You would not need the above changes at all. I did not like it before when 
sympos clearing was proposed, but the situation was different back then. 
'-z unique-symbol' was not available. It has changed and we have a 
guarantee that symbols are unique now. There would not be any impact on 
the user.

What do you think?

Miroslav