[PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

[PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

[Minfei Huang]

From: Minfei Huang <mnfhuang@gmail.com>

The previous patches can be applied, once the corresponding module is
loaded. In general, the patch will do relocation (if necessary) and
obtain/verify function address before we start to enable patch.

There are three different situations in which the coming module notifier
can fail:

1) relocations are not applied for some reason. In this case kallsyms
for module symbol is not called at all. The patch is not applied to the
module. If the user disable and enable patch again, there is possible
bug in klp_enable_func. If the user specified func->old_addr for some
function in the module (and he shouldn't do that, but nevertheless) our
warning would not catch it, ftrace will reject to register the handler
because of wrong address or will register the handler for wrong address.

2) relocations are applied successfully, but kallsyms lookup fails. In
this case func->old_addr can be correct for all previous lookups, 0 for
current failed one, and "unspecified" for the rest. If we undergo the
same scenario as in 1, the behaviour differs for three cases, but the
patch is not enabled anyway.

3) the object is initialized, but klp_enable_object fails in the
notifier due to possible ftrace error. Since it is improbable that
ftrace would heal itself in the future, we would get those errors
everytime the patch is enabled.

In order to fix above situations, we can make obj->mod to NULL, if the
coming modified notifier fails.

Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
---
v4:
- remove the label "out" in function klp_init_object_loaded
v3:
- modify the code style
v2:
- add the error message to make it more friendly
- modify the commit log, base on the mbenes@suse.cz suggesting
v1:
- modify the commit log, describe the issue more details
---
 kernel/livepatch/core.c | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 284e269..4a87765 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -883,7 +883,7 @@ int klp_register_patch(struct klp_patch *patch)
 }
 EXPORT_SYMBOL_GPL(klp_register_patch);
 
-static void klp_module_notify_coming(struct klp_patch *patch,
+static int klp_module_notify_coming(struct klp_patch *patch,
 				     struct klp_object *obj)
 {
 	struct module *pmod = patch->mod;
@@ -891,22 +891,23 @@ static void klp_module_notify_coming(struct klp_patch *patch,
 	int ret;
 
 	ret = klp_init_object_loaded(patch, obj);
-	if (ret)
-		goto err;
+	if (ret) {
+		pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
+			pmod->name, mod->name, ret);
+		return ret;
+	}
 
 	if (patch->state == KLP_DISABLED)
-		return;
+		return 0;
 
 	pr_notice("applying patch '%s' to loading module '%s'\n",
 		  pmod->name, mod->name);
 
 	ret = klp_enable_object(obj);
-	if (!ret)
-		return;
-
-err:
-	pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
-		pmod->name, mod->name, ret);
+	if (ret)
+		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
+			pmod->name, mod->name, ret);
+	return ret;
 }
 
 static void klp_module_notify_going(struct klp_patch *patch,
@@ -930,6 +931,7 @@ disabled:
 static int klp_module_notify(struct notifier_block *nb, unsigned long action,
 			     void *data)
 {
+	int ret;
 	struct module *mod = data;
 	struct klp_patch *patch;
 	struct klp_object *obj;
@@ -955,7 +957,12 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
 
 			if (action == MODULE_STATE_COMING) {
 				obj->mod = mod;
-				klp_module_notify_coming(patch, obj);
+				ret = klp_module_notify_coming(patch, obj);
+				if (ret) {
+					obj->mod = NULL;
+					pr_warn("patch '%s' is in an inconsistent state!\n",
+						patch->mod->name);
+				}
 			} else /* MODULE_STATE_GOING */
 				klp_module_notify_going(patch, obj);
 
-- 
2.2.2

Re: [PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

[Miroslav Benes]

On Fri, 15 May 2015, Minfei Huang wrote:

> From: Minfei Huang <mnfhuang@gmail.com>
> 
> The previous patches can be applied, once the corresponding module is
> loaded. In general, the patch will do relocation (if necessary) and
> obtain/verify function address before we start to enable patch.
> 
> There are three different situations in which the coming module notifier
> can fail:
> 
> 1) relocations are not applied for some reason. In this case kallsyms
> for module symbol is not called at all. The patch is not applied to the
> module. If the user disable and enable patch again, there is possible
> bug in klp_enable_func. If the user specified func->old_addr for some
> function in the module (and he shouldn't do that, but nevertheless) our
> warning would not catch it, ftrace will reject to register the handler
> because of wrong address or will register the handler for wrong address.
> 
> 2) relocations are applied successfully, but kallsyms lookup fails. In
> this case func->old_addr can be correct for all previous lookups, 0 for
> current failed one, and "unspecified" for the rest. If we undergo the
> same scenario as in 1, the behaviour differs for three cases, but the
> patch is not enabled anyway.
> 
> 3) the object is initialized, but klp_enable_object fails in the
> notifier due to possible ftrace error. Since it is improbable that
> ftrace would heal itself in the future, we would get those errors
> everytime the patch is enabled.
> 
> In order to fix above situations, we can make obj->mod to NULL, if the
> coming modified notifier fails.
> 
> Signed-off-by: Minfei Huang <mnfhuang@gmail.com>

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

Regards,
Miroslav


> ---
> v4:
> - remove the label "out" in function klp_init_object_loaded
> v3:
> - modify the code style
> v2:
> - add the error message to make it more friendly
> - modify the commit log, base on the mbenes@suse.cz suggesting
> v1:
> - modify the commit log, describe the issue more details
> ---
>  kernel/livepatch/core.c | 29 ++++++++++++++++++-----------
>  1 file changed, 18 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 284e269..4a87765 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -883,7 +883,7 @@ int klp_register_patch(struct klp_patch *patch)
>  }
>  EXPORT_SYMBOL_GPL(klp_register_patch);
>  
> -static void klp_module_notify_coming(struct klp_patch *patch,
> +static int klp_module_notify_coming(struct klp_patch *patch,
>  				     struct klp_object *obj)
>  {
>  	struct module *pmod = patch->mod;
> @@ -891,22 +891,23 @@ static void klp_module_notify_coming(struct klp_patch *patch,
>  	int ret;
>  
>  	ret = klp_init_object_loaded(patch, obj);
> -	if (ret)
> -		goto err;
> +	if (ret) {
> +		pr_warn("failed to initialize patch '%s' for module '%s' (%d)\n",
> +			pmod->name, mod->name, ret);
> +		return ret;
> +	}
>  
>  	if (patch->state == KLP_DISABLED)
> -		return;
> +		return 0;
>  
>  	pr_notice("applying patch '%s' to loading module '%s'\n",
>  		  pmod->name, mod->name);
>  
>  	ret = klp_enable_object(obj);
> -	if (!ret)
> -		return;
> -
> -err:
> -	pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> -		pmod->name, mod->name, ret);
> +	if (ret)
> +		pr_warn("failed to apply patch '%s' to module '%s' (%d)\n",
> +			pmod->name, mod->name, ret);
> +	return ret;
>  }
>  
>  static void klp_module_notify_going(struct klp_patch *patch,
> @@ -930,6 +931,7 @@ disabled:
>  static int klp_module_notify(struct notifier_block *nb, unsigned long action,
>  			     void *data)
>  {
> +	int ret;
>  	struct module *mod = data;
>  	struct klp_patch *patch;
>  	struct klp_object *obj;
> @@ -955,7 +957,12 @@ static int klp_module_notify(struct notifier_block *nb, unsigned long action,
>  
>  			if (action == MODULE_STATE_COMING) {
>  				obj->mod = mod;
> -				klp_module_notify_coming(patch, obj);
> +				ret = klp_module_notify_coming(patch, obj);
> +				if (ret) {
> +					obj->mod = NULL;
> +					pr_warn("patch '%s' is in an inconsistent state!\n",
> +						patch->mod->name);
> +				}
>  			} else /* MODULE_STATE_GOING */
>  				klp_module_notify_going(patch, obj);
>  
> -- 
> 2.2.2
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Re: [PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

[Josh Poimboeuf]

On Fri, May 15, 2015 at 10:22:48AM +0800, Minfei Huang wrote:
> From: Minfei Huang <mnfhuang@gmail.com>
> 
> The previous patches can be applied, once the corresponding module is
> loaded. In general, the patch will do relocation (if necessary) and
> obtain/verify function address before we start to enable patch.
> 
> There are three different situations in which the coming module notifier
> can fail:
> 
> 1) relocations are not applied for some reason. In this case kallsyms
> for module symbol is not called at all. The patch is not applied to the
> module. If the user disable and enable patch again, there is possible
> bug in klp_enable_func. If the user specified func->old_addr for some
> function in the module (and he shouldn't do that, but nevertheless) our
> warning would not catch it, ftrace will reject to register the handler
> because of wrong address or will register the handler for wrong address.
> 
> 2) relocations are applied successfully, but kallsyms lookup fails. In
> this case func->old_addr can be correct for all previous lookups, 0 for
> current failed one, and "unspecified" for the rest. If we undergo the
> same scenario as in 1, the behaviour differs for three cases, but the
> patch is not enabled anyway.
> 
> 3) the object is initialized, but klp_enable_object fails in the
> notifier due to possible ftrace error. Since it is improbable that
> ftrace would heal itself in the future, we would get those errors
> everytime the patch is enabled.
> 
> In order to fix above situations, we can make obj->mod to NULL, if the
> coming modified notifier fails.
> 
> Signed-off-by: Minfei Huang <mnfhuang@gmail.com>

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

Thanks!

-- 
Josh

Re: [PATCH v5] livepatch: Prevent patch inconsistencies if the coming module notifier fails

[Jiri Kosina]

On Fri, 15 May 2015, Minfei Huang wrote:

> From: Minfei Huang <mnfhuang@gmail.com>
> 
> The previous patches can be applied, once the corresponding module is
> loaded. In general, the patch will do relocation (if necessary) and
> obtain/verify function address before we start to enable patch.
> 
> There are three different situations in which the coming module notifier
> can fail:
> 
> 1) relocations are not applied for some reason. In this case kallsyms
> for module symbol is not called at all. The patch is not applied to the
> module. If the user disable and enable patch again, there is possible
> bug in klp_enable_func. If the user specified func->old_addr for some
> function in the module (and he shouldn't do that, but nevertheless) our
> warning would not catch it, ftrace will reject to register the handler
> because of wrong address or will register the handler for wrong address.
> 
> 2) relocations are applied successfully, but kallsyms lookup fails. In
> this case func->old_addr can be correct for all previous lookups, 0 for
> current failed one, and "unspecified" for the rest. If we undergo the
> same scenario as in 1, the behaviour differs for three cases, but the
> patch is not enabled anyway.
> 
> 3) the object is initialized, but klp_enable_object fails in the
> notifier due to possible ftrace error. Since it is improbable that
> ftrace would heal itself in the future, we would get those errors
> everytime the patch is enabled.
> 
> In order to fix above situations, we can make obj->mod to NULL, if the
> coming modified notifier fails.
> 
> Signed-off-by: Minfei Huang <mnfhuang@gmail.com>
> ---
> v4:
> - remove the label "out" in function klp_init_object_loaded
> v3:
> - modify the code style
> v2:
> - add the error message to make it more friendly
> - modify the commit log, base on the mbenes@suse.cz suggesting
> v1:
> - modify the commit log, describe the issue more details

Applied to for-4.2/upstream branch. Thanks,

-- 
Jiri Kosina
SUSE Labs