linux-kernel - Re: [POC 03/23] livepatch: Better checks of struct klp

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Date:   Tue, 21 Jan 2020 11:27:17 +0000
From:   Julien Thierry <jthierry@...hat.com>
To:     Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>,
        Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [POC 03/23] livepatch: Better checks of struct klp_object
 definition

Hi Petr,

On 1/17/20 3:03 PM, Petr Mladek wrote:
> The number of user defined fields increased in struct klp_object after
> spliting per-object livepatches. It was sometimes unclear why exactly
> the module could not get loded when returned -EINVAL.
> 
> Add more checks for the split modules and write useful error
> messages on particular errors.
> 
> Signed-off-by: Petr Mladek <pmladek@...e.com>
> ---
>   kernel/livepatch/core.c | 91 ++++++++++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 82 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index bb62c5407b75..ec7ffc7db3a7 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -756,9 +756,6 @@ static int klp_init_object(struct klp_patch *patch, struct klp_object *obj)
>   	int ret;
>   	const char *name;
>   
> -	if (klp_is_module(obj) && strlen(obj->name) >= MODULE_NAME_LEN)
> -		return -EINVAL;
> -
>   	obj->patched = false;
>   
>   	name = obj->name ? obj->name : "vmlinux";
> @@ -851,8 +848,86 @@ static int klp_init_patch(struct klp_patch *patch)
>   	return 0;
>   }
>   
> +static int klp_check_module_name(struct klp_object *obj, bool is_module)
> +{
> +	char mod_name[MODULE_NAME_LEN];
> +	const char *expected_name;
> +
> +	if (is_module) {
> +		snprintf(mod_name, sizeof(mod_name), "%s__%s",
> +			 obj->patch_name, obj->name);
> +		expected_name = mod_name;
> +	} else {
> +		expected_name = obj->patch_name;
> +	}
> +
> +	if (strcmp(expected_name, obj->mod->name)) {

I'm not sure I understand the point of enforcing this.

> +		pr_err("The module name %s does not match with obj->patch_name and obj->name. The expected name is: %s\n",
> +		       obj->mod->name, expected_name);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int klp_check_object(struct klp_object *obj, bool is_module)
> +{
> +
> +	if (!obj->mod)
> +		return -EINVAL;
> +
> +	if (!is_livepatch_module(obj->mod)) {
> +		pr_err("module %s is not marked as a livepatch module\n",
> +		       obj->mod->name);
> +		return -EINVAL;
> +	}
> +
> +	if (!obj->patch_name) {
> +		pr_err("module %s does not have set obj->patch_name\n",
> +		       obj->mod->name);
> +		return -EINVAL;
> +	}
> +
> +	if (strlen(obj->patch_name) >= MODULE_NAME_LEN) {
> +		pr_err("module %s has too long obj->patch_name\n",
> +		       obj->mod->name);
> +		return -EINVAL;
> +	}
> +
> +	if (is_module) {
> +		if (!obj->name) {
> +			pr_err("module %s does not have set obj->name\n",
> +			       obj->mod->name);
> +			return -EINVAL;
> +		}
> +		if (strlen(obj->name) >= MODULE_NAME_LEN) {
> +			pr_err("module %s has too long obj->name\n",
> +			       obj->mod->name);
> +			return -EINVAL;
> +		}
> +	} else if (obj->name) {
> +		pr_err("module %s for vmlinux must not have set obj->name\n",
> +		       obj->mod->name);
> +		return -EINVAL;
> +	}
> +
> +	if (!obj->funcs) {
> +		pr_err("module %s does not have set obj->funcs\n",
> +		       obj->mod->name);
> +		return -EINVAL;
> +	}
> +
> +	return klp_check_module_name(obj, is_module);
> +}
> +
>   int klp_add_object(struct klp_object *obj)
>   {
> +	int ret;
> +
> +	ret = klp_check_object(obj, true);
> +	if (ret)
> +		return ret;
> +
>   	return 0;
>   }
>   EXPORT_SYMBOL_GPL(klp_add_object);
> @@ -958,14 +1033,12 @@ int klp_enable_patch(struct klp_patch *patch)
>   {
>   	int ret;
>   
> -	if (!patch || !patch->obj || !patch->obj->mod)
> +	if (!patch || !patch->obj)
>   		return -EINVAL;
>   
> -	if (!is_livepatch_module(patch->obj->mod)) {
> -		pr_err("module %s is not marked as a livepatch module\n",
> -		       patch->obj->patch_name);
> -		return -EINVAL;
> -	}
> +	ret = klp_check_object(patch->obj, false);
> +	if (ret)
> +		return ret;
>   
>   	if (!klp_initialized())
>   		return -ENODEV;
> 

Otherwise this looks good to me.

Cheers,

-- 
Julien Thierry