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livepatch-patch-hook: add comments

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Add some commentary to the livepatch-patch-hook file to explain what
it's doing.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
This commit is contained in:
Joe Lawrence 2020-07-24 15:33:28 -04:00 committed by Artem Savkov
parent cc5200fbf8
commit 607ee53e1e
1 changed files with 106 additions and 0 deletions
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106
kmod/patch/livepatch-patch-hook.c
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@ -104,10 +104,28 @@
* done, the scaffold structs are no longer needed.
*/
/*
* lpatch is the kernel data structure that will be created on patch
* init, registered with the livepatch API on init, and finally
* unregistered when the patch exits. Its struct klp_object *objs
* member must be dynamically allocated according to the number of
* target objects it will be patching.
*/
static struct klp_patch *lpatch;
static LIST_HEAD(patch_objects);
static int patch_objects_nr;
/**
* struct patch_object - scaffolding structure tracking patch target objects
* @list: list of patch_object (threaded onto patch_objects)
* @funcs: list of patch_func associated with this object
* @relocs: list of patch_reloc associated with this object
* @callbacks: kernel struct of object callbacks
* @name: patch target object name (NULL for vmlinux)
* @funcs_nr: count of kpatch_patch_func added to @funcs
* @relocs_nr: count of patch_reloc added to @relocs
*/
struct patch_object {
struct list_head list;
struct list_head funcs;
@ -119,16 +137,36 @@ struct patch_object {
int funcs_nr, relocs_nr;
};
/**
* struct patch_func - scaffolding structure for kpatch_patch_func
* @list: list of patch_func (threaded onto patch_object.funcs)
* @kfunc: array of kpatch_patch_func
*/
struct patch_func {
struct list_head list;
struct kpatch_patch_func *kfunc;
};
/**
* struct patch_reloc - scaffolding structure for kpatch_patch_dynrela
* @list: list of patch_reloc (threaded onto patch_object.relocs)
* @kdynrela: array of kpatch_patch_dynrela
*/
struct patch_reloc {
struct list_head list;
struct kpatch_patch_dynrela *kdynrela;
};
/**
* patch_alloc_new_object() - creates and initializes a new patch_object
* @name: target object name
*
* Return: pointer to new patch_object, NULL on failure.
*
* Does not check for previously created patch_objects with the same
* name. Updates patch_objects_nr and threads new data structure onto
* the patch_objects list.
*/
static struct patch_object *patch_alloc_new_object(const char *name)
{
struct patch_object *object;
@ -147,6 +185,16 @@ static struct patch_object *patch_alloc_new_object(const char *name)
return object;
}
/**
* patch_find_object_by_name() - find or create a patch_object with a
* given name
* @name: target object name
*
* Return: pointer to patch_object, NULL on failure.
*
* Searches the patch_objects list for an already created instance with
* @name, otherwise tries to create it via patch_alloc_new_object()
*/
static struct patch_object *patch_find_object_by_name(const char *name)
{
struct patch_object *object;
@ -158,6 +206,17 @@ static struct patch_object *patch_find_object_by_name(const char *name)
return patch_alloc_new_object(name);
}
/**
* patch_add_func_to_object() - create scaffolding from kpatch_patch_func data
*
* @kfunc: Individual kpatch_patch_func pointer
*
* Return: 0 on success, -ENOMEM on failure.
*
* Builds scaffolding data structures from .kpatch.funcs section's array
* of kpatch_patch_func structures. Updates the associated
* patch_object's funcs_nr count.
*/
static int patch_add_func_to_object(struct kpatch_patch_func *kfunc)
{
struct patch_func *func;
@ -180,6 +239,17 @@ static int patch_add_func_to_object(struct kpatch_patch_func *kfunc)
}
#ifndef HAVE_ELF_RELOCS
/**
* patch_add_reloc_to_object() - create scaffolding from kpatch_patch_dynrela data
*
* @kdynrela: Individual kpatch_patch_dynrela pointer
*
* Return: 0 on success, -ENOMEM on failure.
*
* Builds scaffolding data structures from .kpatch.dynrelas section's array
* of kpatch_patch_dynrela structures. Updates the associated
* patch_object's relocs_nr count.
*/
static int patch_add_reloc_to_object(struct kpatch_patch_dynrela *kdynrela)
{
struct patch_reloc *reloc;
@ -202,6 +272,9 @@ static int patch_add_reloc_to_object(struct kpatch_patch_dynrela *kdynrela)
}
#endif
/**
* patch_free_scaffold() - tear down the temporary kpatch scaffolding
*/
static void patch_free_scaffold(void) {
struct patch_func *func, *safefunc;
struct patch_object *object, *safeobject;
@ -227,6 +300,9 @@ static void patch_free_scaffold(void) {
}
}
/**
* patch_free_livepatch() - release the klp_patch and friends
*/
static void patch_free_livepatch(struct klp_patch *patch)
{
struct klp_object *object;
@ -246,12 +322,21 @@ static void patch_free_livepatch(struct klp_patch *patch)
}
}
/* Defined by kpatch.lds.S */
extern struct kpatch_pre_patch_callback __kpatch_callbacks_pre_patch[], __kpatch_callbacks_pre_patch_end[];
extern struct kpatch_post_patch_callback __kpatch_callbacks_post_patch[], __kpatch_callbacks_post_patch_end[];
extern struct kpatch_pre_unpatch_callback __kpatch_callbacks_pre_unpatch[], __kpatch_callbacks_pre_unpatch_end[];
extern struct kpatch_post_unpatch_callback __kpatch_callbacks_post_unpatch[], __kpatch_callbacks_post_unpatch_end[];
#ifdef HAVE_CALLBACKS
/**
* add_callbacks_to_patch_objects() - create patch_objects that have callbacks
*
* Return: 0 on success, -ENOMEM or -EINVAL on failure
*
* Iterates through all kpatch pre/post-(un)patch callback data
* structures and creates scaffolding patch_objects for them.
*/
static int add_callbacks_to_patch_objects(void)
{
struct kpatch_pre_patch_callback *p_pre_patch_callback;
@ -341,6 +426,7 @@ static inline int add_callbacks_to_patch_objects(void)
}
#endif /* HAVE_CALLBACKS */
/* Defined by kpatch.lds.S */
extern struct kpatch_patch_func __kpatch_funcs[], __kpatch_funcs_end[];
#ifndef HAVE_ELF_RELOCS
extern struct kpatch_patch_dynrela __kpatch_dynrelas[], __kpatch_dynrelas_end[];
@ -360,6 +446,12 @@ static int __init patch_init(void)
struct klp_reloc *lrelocs, *lreloc;
#endif
/*
* Step 1 - read from output.o, create temporary scaffolding
* data-structures
*/
/* organize functions and relocs by object in scaffold */
for (kfunc = __kpatch_funcs;
kfunc != __kpatch_funcs_end;
@ -386,6 +478,16 @@ static int __init patch_init(void)
/* past this point, only possible return code is -ENOMEM */
ret = -ENOMEM;
/*
* Step 2 - create livepatch klp_patch and friends
*
* There are two dynamically allocated parts:
*
* klp_patch
* klp_object objs [patch_objects_nr] <= i
* klp_func funcs [object->funcs_nr] <= j
*/
/* allocate and fill livepatch structures */
lpatch = kzalloc(sizeof(*lpatch), GFP_KERNEL);
if (!lpatch)
@ -456,6 +558,10 @@ static int __init patch_init(void)
i++;
}
/*
* Step 3 - throw away scaffolding
*/
/*
* Once the patch structure that the live patching API expects
* has been built, we can release the scaffold structure.