xref: /openbmc/linux/kernel/livepatch/state.c (revision 7b7b8a2c)
1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3  * system_state.c - State of the system modified by livepatches
4  *
5  * Copyright (C) 2019 SUSE
6  */
7 
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 
10 #include <linux/livepatch.h>
11 #include "core.h"
12 #include "state.h"
13 #include "transition.h"
14 
15 #define klp_for_each_state(patch, state)		\
16 	for (state = patch->states; state && state->id; state++)
17 
18 /**
19  * klp_get_state() - get information about system state modified by
20  *	the given patch
21  * @patch:	livepatch that modifies the given system state
22  * @id:		custom identifier of the modified system state
23  *
24  * Checks whether the given patch modifies the given system state.
25  *
26  * The function can be called either from pre/post (un)patch
27  * callbacks or from the kernel code added by the livepatch.
28  *
29  * Return: pointer to struct klp_state when found, otherwise NULL.
30  */
klp_get_state(struct klp_patch * patch,unsigned long id)31 struct klp_state *klp_get_state(struct klp_patch *patch, unsigned long id)
32 {
33 	struct klp_state *state;
34 
35 	klp_for_each_state(patch, state) {
36 		if (state->id == id)
37 			return state;
38 	}
39 
40 	return NULL;
41 }
42 EXPORT_SYMBOL_GPL(klp_get_state);
43 
44 /**
45  * klp_get_prev_state() - get information about system state modified by
46  *	the already installed livepatches
47  * @id:		custom identifier of the modified system state
48  *
49  * Checks whether already installed livepatches modify the given
50  * system state.
51  *
52  * The same system state can be modified by more non-cumulative
53  * livepatches. It is expected that the latest livepatch has
54  * the most up-to-date information.
55  *
56  * The function can be called only during transition when a new
57  * livepatch is being enabled or when such a transition is reverted.
58  * It is typically called only from pre/post (un)patch
59  * callbacks.
60  *
61  * Return: pointer to the latest struct klp_state from already
62  *	installed livepatches, NULL when not found.
63  */
klp_get_prev_state(unsigned long id)64 struct klp_state *klp_get_prev_state(unsigned long id)
65 {
66 	struct klp_patch *patch;
67 	struct klp_state *state, *last_state = NULL;
68 
69 	if (WARN_ON_ONCE(!klp_transition_patch))
70 		return NULL;
71 
72 	klp_for_each_patch(patch) {
73 		if (patch == klp_transition_patch)
74 			goto out;
75 
76 		state = klp_get_state(patch, id);
77 		if (state)
78 			last_state = state;
79 	}
80 
81 out:
82 	return last_state;
83 }
84 EXPORT_SYMBOL_GPL(klp_get_prev_state);
85 
86 /* Check if the patch is able to deal with the existing system state. */
klp_is_state_compatible(struct klp_patch * patch,struct klp_state * old_state)87 static bool klp_is_state_compatible(struct klp_patch *patch,
88 				    struct klp_state *old_state)
89 {
90 	struct klp_state *state;
91 
92 	state = klp_get_state(patch, old_state->id);
93 
94 	/* A cumulative livepatch must handle all already modified states. */
95 	if (!state)
96 		return !patch->replace;
97 
98 	return state->version >= old_state->version;
99 }
100 
101 /*
102  * Check that the new livepatch will not break the existing system states.
103  * Cumulative patches must handle all already modified states.
104  * Non-cumulative patches can touch already modified states.
105  */
klp_is_patch_compatible(struct klp_patch * patch)106 bool klp_is_patch_compatible(struct klp_patch *patch)
107 {
108 	struct klp_patch *old_patch;
109 	struct klp_state *old_state;
110 
111 	klp_for_each_patch(old_patch) {
112 		klp_for_each_state(old_patch, old_state) {
113 			if (!klp_is_state_compatible(patch, old_state))
114 				return false;
115 		}
116 	}
117 
118 	return true;
119 }
120