1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Intel Memory Protection Keys management
4 * Copyright (c) 2015, Intel Corporation.
5 */
6 #include <linux/debugfs.h> /* debugfs_create_u32() */
7 #include <linux/mm_types.h> /* mm_struct, vma, etc... */
8 #include <linux/pkeys.h> /* PKEY_* */
9 #include <uapi/asm-generic/mman-common.h>
10
11 #include <asm/cpufeature.h> /* boot_cpu_has, ... */
12 #include <asm/mmu_context.h> /* vma_pkey() */
13
14 int __execute_only_pkey(struct mm_struct *mm)
15 {
16 bool need_to_set_mm_pkey = false;
17 int execute_only_pkey = mm->context.execute_only_pkey;
18 int ret;
19
20 /* Do we need to assign a pkey for mm's execute-only maps? */
21 if (execute_only_pkey == -1) {
22 /* Go allocate one to use, which might fail */
23 execute_only_pkey = mm_pkey_alloc(mm);
24 if (execute_only_pkey < 0)
25 return -1;
26 need_to_set_mm_pkey = true;
27 }
28
29 /*
30 * We do not want to go through the relatively costly
31 * dance to set PKRU if we do not need to. Check it
32 * first and assume that if the execute-only pkey is
33 * write-disabled that we do not have to set it
34 * ourselves.
35 */
36 if (!need_to_set_mm_pkey &&
37 !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
38 return execute_only_pkey;
39 }
40
41 /*
42 * Set up PKRU so that it denies access for everything
43 * other than execution.
44 */
45 ret = arch_set_user_pkey_access(current, execute_only_pkey,
46 PKEY_DISABLE_ACCESS);
47 /*
48 * If the PKRU-set operation failed somehow, just return
49 * 0 and effectively disable execute-only support.
50 */
51 if (ret) {
52 mm_set_pkey_free(mm, execute_only_pkey);
53 return -1;
54 }
55
56 /* We got one, store it and use it from here on out */
57 if (need_to_set_mm_pkey)
58 mm->context.execute_only_pkey = execute_only_pkey;
59 return execute_only_pkey;
60 }
61
62 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
63 {
64 /* Do this check first since the vm_flags should be hot */
65 if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC)
66 return false;
67 if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey)
68 return false;
69
70 return true;
71 }
72
73 /*
74 * This is only called for *plain* mprotect calls.
75 */
76 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey)
77 {
78 /*
79 * Is this an mprotect_pkey() call? If so, never
80 * override the value that came from the user.
81 */
82 if (pkey != -1)
83 return pkey;
84
85 /*
86 * The mapping is execute-only. Go try to get the
87 * execute-only protection key. If we fail to do that,
88 * fall through as if we do not have execute-only
89 * support in this mm.
90 */
91 if (prot == PROT_EXEC) {
92 pkey = execute_only_pkey(vma->vm_mm);
93 if (pkey > 0)
94 return pkey;
95 } else if (vma_is_pkey_exec_only(vma)) {
96 /*
97 * Protections are *not* PROT_EXEC, but the mapping
98 * is using the exec-only pkey. This mapping was
99 * PROT_EXEC and will no longer be. Move back to
100 * the default pkey.
101 */
102 return ARCH_DEFAULT_PKEY;
103 }
104
105 /*
106 * This is a vanilla, non-pkey mprotect (or we failed to
107 * setup execute-only), inherit the pkey from the VMA we
108 * are working on.
109 */
110 return vma_pkey(vma);
111 }
112
113 #define PKRU_AD_MASK(pkey) (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY))
114
115 /*
116 * Make the default PKRU value (at execve() time) as restrictive
117 * as possible. This ensures that any threads clone()'d early
118 * in the process's lifetime will not accidentally get access
119 * to data which is pkey-protected later on.
120 */
121 u32 init_pkru_value = PKRU_AD_MASK( 1) | PKRU_AD_MASK( 2) |
122 PKRU_AD_MASK( 3) | PKRU_AD_MASK( 4) |
123 PKRU_AD_MASK( 5) | PKRU_AD_MASK( 6) |
124 PKRU_AD_MASK( 7) | PKRU_AD_MASK( 8) |
125 PKRU_AD_MASK( 9) | PKRU_AD_MASK(10) |
126 PKRU_AD_MASK(11) | PKRU_AD_MASK(12) |
127 PKRU_AD_MASK(13) | PKRU_AD_MASK(14) |
128 PKRU_AD_MASK(15);
129
130 static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf,
131 size_t count, loff_t *ppos)
132 {
133 char buf[32];
134 unsigned int len;
135
136 len = sprintf(buf, "0x%x\n", init_pkru_value);
137 return simple_read_from_buffer(user_buf, count, ppos, buf, len);
138 }
139
140 static ssize_t init_pkru_write_file(struct file *file,
141 const char __user *user_buf, size_t count, loff_t *ppos)
142 {
143 char buf[32];
144 ssize_t len;
145 u32 new_init_pkru;
146
147 len = min(count, sizeof(buf) - 1);
148 if (copy_from_user(buf, user_buf, len))
149 return -EFAULT;
150
151 /* Make the buffer a valid string that we can not overrun */
152 buf[len] = '\0';
153 if (kstrtouint(buf, 0, &new_init_pkru))
154 return -EINVAL;
155
156 /*
157 * Don't allow insane settings that will blow the system
158 * up immediately if someone attempts to disable access
159 * or writes to pkey 0.
160 */
161 if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT))
162 return -EINVAL;
163
164 WRITE_ONCE(init_pkru_value, new_init_pkru);
165 return count;
166 }
167
168 static const struct file_operations fops_init_pkru = {
169 .read = init_pkru_read_file,
170 .write = init_pkru_write_file,
171 .llseek = default_llseek,
172 };
173
174 static int __init create_init_pkru_value(void)
175 {
176 /* Do not expose the file if pkeys are not supported. */
177 if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
178 return 0;
179
180 debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR,
181 arch_debugfs_dir, NULL, &fops_init_pkru);
182 return 0;
183 }
184 late_initcall(create_init_pkru_value);
185
186 static __init int setup_init_pkru(char *opt)
187 {
188 u32 new_init_pkru;
189
190 if (kstrtouint(opt, 0, &new_init_pkru))
191 return 1;
192
193 WRITE_ONCE(init_pkru_value, new_init_pkru);
194
195 return 1;
196 }
197 __setup("init_pkru=", setup_init_pkru);
198
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