1 // SPDX-License-Identifier: MIT
2 /*
3  * Copyright © 2021 Intel Corporation
4  */
5 
6 #include <linux/kernel.h>
7 #include <linux/moduleparam.h>
8 #include <linux/slab.h>
9 #include <linux/string.h>
10 
11 #include "i915_driver.h"
12 #include "i915_drv.h"
13 #include "i915_mitigations.h"
14 
15 static unsigned long mitigations __read_mostly = ~0UL;
16 
17 enum {
18 	CLEAR_RESIDUALS = 0,
19 };
20 
21 static const char * const names[] = {
22 	[CLEAR_RESIDUALS] = "residuals",
23 };
24 
25 bool i915_mitigate_clear_residuals(void)
26 {
27 	return READ_ONCE(mitigations) & BIT(CLEAR_RESIDUALS);
28 }
29 
30 static int mitigations_set(const char *val, const struct kernel_param *kp)
31 {
32 	unsigned long new = ~0UL;
33 	char *str, *sep, *tok;
34 	bool first = true;
35 	int err = 0;
36 
37 	BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
38 
39 	str = kstrdup(val, GFP_KERNEL);
40 	if (!str)
41 		return -ENOMEM;
42 
43 	for (sep = str; (tok = strsep(&sep, ","));) {
44 		bool enable = true;
45 		int i;
46 
47 		/* Be tolerant of leading/trailing whitespace */
48 		tok = strim(tok);
49 
50 		if (first) {
51 			first = false;
52 
53 			if (!strcmp(tok, "auto"))
54 				continue;
55 
56 			new = 0;
57 			if (!strcmp(tok, "off"))
58 				continue;
59 		}
60 
61 		if (*tok == '!') {
62 			enable = !enable;
63 			tok++;
64 		}
65 
66 		if (!strncmp(tok, "no", 2)) {
67 			enable = !enable;
68 			tok += 2;
69 		}
70 
71 		if (*tok == '\0')
72 			continue;
73 
74 		for (i = 0; i < ARRAY_SIZE(names); i++) {
75 			if (!strcmp(tok, names[i])) {
76 				if (enable)
77 					new |= BIT(i);
78 				else
79 					new &= ~BIT(i);
80 				break;
81 			}
82 		}
83 		if (i == ARRAY_SIZE(names)) {
84 			pr_err("Bad \"%s.mitigations=%s\", '%s' is unknown\n",
85 			       DRIVER_NAME, val, tok);
86 			err = -EINVAL;
87 			break;
88 		}
89 	}
90 	kfree(str);
91 	if (err)
92 		return err;
93 
94 	WRITE_ONCE(mitigations, new);
95 	return 0;
96 }
97 
98 static int mitigations_get(char *buffer, const struct kernel_param *kp)
99 {
100 	unsigned long local = READ_ONCE(mitigations);
101 	int count, i;
102 	bool enable;
103 
104 	if (!local)
105 		return scnprintf(buffer, PAGE_SIZE, "%s\n", "off");
106 
107 	if (local & BIT(BITS_PER_LONG - 1)) {
108 		count = scnprintf(buffer, PAGE_SIZE, "%s,", "auto");
109 		enable = false;
110 	} else {
111 		enable = true;
112 		count = 0;
113 	}
114 
115 	for (i = 0; i < ARRAY_SIZE(names); i++) {
116 		if ((local & BIT(i)) != enable)
117 			continue;
118 
119 		count += scnprintf(buffer + count, PAGE_SIZE - count,
120 				   "%s%s,", enable ? "" : "!", names[i]);
121 	}
122 
123 	buffer[count - 1] = '\n';
124 	return count;
125 }
126 
127 static const struct kernel_param_ops ops = {
128 	.set = mitigations_set,
129 	.get = mitigations_get,
130 };
131 
132 module_param_cb_unsafe(mitigations, &ops, NULL, 0600);
133 MODULE_PARM_DESC(mitigations,
134 "Selectively enable security mitigations for all Intel® GPUs in the system.\n"
135 "\n"
136 "  auto -- enables all mitigations required for the platform [default]\n"
137 "  off  -- disables all mitigations\n"
138 "\n"
139 "Individual mitigations can be enabled by passing a comma-separated string,\n"
140 "e.g. mitigations=residuals to enable only clearing residuals or\n"
141 "mitigations=auto,noresiduals to disable only the clear residual mitigation.\n"
142 "Either '!' or 'no' may be used to switch from enabling the mitigation to\n"
143 "disabling it.\n"
144 "\n"
145 "Active mitigations for Ivybridge, Baytrail, Haswell:\n"
146 "  residuals -- clear all thread-local registers between contexts"
147 );
148