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62b5f7d0 DH |
1 | /* |
2 | * Intel Memory Protection Keys management | |
3 | * Copyright (c) 2015, Intel Corporation. | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify it | |
6 | * under the terms and conditions of the GNU General Public License, | |
7 | * version 2, as published by the Free Software Foundation. | |
8 | * | |
9 | * This program is distributed in the hope it will be useful, but WITHOUT | |
10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for | |
12 | * more details. | |
13 | */ | |
76de9937 | 14 | #include <linux/debugfs.h> /* debugfs_create_u32() */ |
62b5f7d0 DH |
15 | #include <linux/mm_types.h> /* mm_struct, vma, etc... */ |
16 | #include <linux/pkeys.h> /* PKEY_* */ | |
17 | #include <uapi/asm-generic/mman-common.h> | |
18 | ||
19 | #include <asm/cpufeature.h> /* boot_cpu_has, ... */ | |
20 | #include <asm/mmu_context.h> /* vma_pkey() */ | |
62b5f7d0 DH |
21 | |
22 | int __execute_only_pkey(struct mm_struct *mm) | |
23 | { | |
e8c24d3a DH |
24 | bool need_to_set_mm_pkey = false; |
25 | int execute_only_pkey = mm->context.execute_only_pkey; | |
62b5f7d0 DH |
26 | int ret; |
27 | ||
e8c24d3a DH |
28 | /* Do we need to assign a pkey for mm's execute-only maps? */ |
29 | if (execute_only_pkey == -1) { | |
30 | /* Go allocate one to use, which might fail */ | |
31 | execute_only_pkey = mm_pkey_alloc(mm); | |
32 | if (execute_only_pkey < 0) | |
33 | return -1; | |
34 | need_to_set_mm_pkey = true; | |
35 | } | |
36 | ||
62b5f7d0 DH |
37 | /* |
38 | * We do not want to go through the relatively costly | |
39 | * dance to set PKRU if we do not need to. Check it | |
40 | * first and assume that if the execute-only pkey is | |
41 | * write-disabled that we do not have to set it | |
42 | * ourselves. We need preempt off so that nobody | |
43 | * can make fpregs inactive. | |
44 | */ | |
45 | preempt_disable(); | |
e8c24d3a | 46 | if (!need_to_set_mm_pkey && |
e4a81bfc | 47 | current->thread.fpu.initialized && |
e8c24d3a | 48 | !__pkru_allows_read(read_pkru(), execute_only_pkey)) { |
62b5f7d0 | 49 | preempt_enable(); |
e8c24d3a | 50 | return execute_only_pkey; |
62b5f7d0 DH |
51 | } |
52 | preempt_enable(); | |
e8c24d3a DH |
53 | |
54 | /* | |
55 | * Set up PKRU so that it denies access for everything | |
56 | * other than execution. | |
57 | */ | |
58 | ret = arch_set_user_pkey_access(current, execute_only_pkey, | |
62b5f7d0 DH |
59 | PKEY_DISABLE_ACCESS); |
60 | /* | |
61 | * If the PKRU-set operation failed somehow, just return | |
62 | * 0 and effectively disable execute-only support. | |
63 | */ | |
e8c24d3a DH |
64 | if (ret) { |
65 | mm_set_pkey_free(mm, execute_only_pkey); | |
66 | return -1; | |
67 | } | |
62b5f7d0 | 68 | |
e8c24d3a DH |
69 | /* We got one, store it and use it from here on out */ |
70 | if (need_to_set_mm_pkey) | |
71 | mm->context.execute_only_pkey = execute_only_pkey; | |
72 | return execute_only_pkey; | |
62b5f7d0 DH |
73 | } |
74 | ||
75 | static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma) | |
76 | { | |
77 | /* Do this check first since the vm_flags should be hot */ | |
78 | if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC) | |
79 | return false; | |
e8c24d3a | 80 | if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey) |
62b5f7d0 DH |
81 | return false; |
82 | ||
83 | return true; | |
84 | } | |
85 | ||
86 | /* | |
87 | * This is only called for *plain* mprotect calls. | |
88 | */ | |
89 | int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey) | |
90 | { | |
91 | /* | |
92 | * Is this an mprotect_pkey() call? If so, never | |
93 | * override the value that came from the user. | |
94 | */ | |
95 | if (pkey != -1) | |
96 | return pkey; | |
97 | /* | |
98 | * Look for a protection-key-drive execute-only mapping | |
99 | * which is now being given permissions that are not | |
100 | * execute-only. Move it back to the default pkey. | |
101 | */ | |
102 | if (vma_is_pkey_exec_only(vma) && | |
103 | (prot & (PROT_READ|PROT_WRITE))) { | |
104 | return 0; | |
105 | } | |
106 | /* | |
107 | * The mapping is execute-only. Go try to get the | |
108 | * execute-only protection key. If we fail to do that, | |
109 | * fall through as if we do not have execute-only | |
110 | * support. | |
111 | */ | |
112 | if (prot == PROT_EXEC) { | |
113 | pkey = execute_only_pkey(vma->vm_mm); | |
114 | if (pkey > 0) | |
115 | return pkey; | |
116 | } | |
117 | /* | |
118 | * This is a vanilla, non-pkey mprotect (or we failed to | |
119 | * setup execute-only), inherit the pkey from the VMA we | |
120 | * are working on. | |
121 | */ | |
122 | return vma_pkey(vma); | |
123 | } | |
acd547b2 DH |
124 | |
125 | #define PKRU_AD_KEY(pkey) (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY)) | |
126 | ||
127 | /* | |
128 | * Make the default PKRU value (at execve() time) as restrictive | |
129 | * as possible. This ensures that any threads clone()'d early | |
130 | * in the process's lifetime will not accidentally get access | |
131 | * to data which is pkey-protected later on. | |
132 | */ | |
133 | u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) | | |
134 | PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) | | |
135 | PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) | | |
136 | PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) | | |
137 | PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15); | |
138 | ||
139 | /* | |
140 | * Called from the FPU code when creating a fresh set of FPU | |
141 | * registers. This is called from a very specific context where | |
142 | * we know the FPU regstiers are safe for use and we can use PKRU | |
e6365084 | 143 | * directly. |
acd547b2 DH |
144 | */ |
145 | void copy_init_pkru_to_fpregs(void) | |
146 | { | |
147 | u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value); | |
148 | /* | |
149 | * Any write to PKRU takes it out of the XSAVE 'init | |
150 | * state' which increases context switch cost. Avoid | |
151 | * writing 0 when PKRU was already 0. | |
152 | */ | |
153 | if (!init_pkru_value_snapshot && !read_pkru()) | |
154 | return; | |
155 | /* | |
156 | * Override the PKRU state that came from 'init_fpstate' | |
157 | * with the baseline from the process. | |
158 | */ | |
159 | write_pkru(init_pkru_value_snapshot); | |
160 | } | |
76de9937 DH |
161 | |
162 | static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf, | |
163 | size_t count, loff_t *ppos) | |
164 | { | |
165 | char buf[32]; | |
166 | unsigned int len; | |
167 | ||
168 | len = sprintf(buf, "0x%x\n", init_pkru_value); | |
169 | return simple_read_from_buffer(user_buf, count, ppos, buf, len); | |
170 | } | |
171 | ||
172 | static ssize_t init_pkru_write_file(struct file *file, | |
173 | const char __user *user_buf, size_t count, loff_t *ppos) | |
174 | { | |
175 | char buf[32]; | |
176 | ssize_t len; | |
177 | u32 new_init_pkru; | |
178 | ||
179 | len = min(count, sizeof(buf) - 1); | |
180 | if (copy_from_user(buf, user_buf, len)) | |
181 | return -EFAULT; | |
182 | ||
183 | /* Make the buffer a valid string that we can not overrun */ | |
184 | buf[len] = '\0'; | |
185 | if (kstrtouint(buf, 0, &new_init_pkru)) | |
186 | return -EINVAL; | |
187 | ||
188 | /* | |
189 | * Don't allow insane settings that will blow the system | |
190 | * up immediately if someone attempts to disable access | |
191 | * or writes to pkey 0. | |
192 | */ | |
193 | if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT)) | |
194 | return -EINVAL; | |
195 | ||
196 | WRITE_ONCE(init_pkru_value, new_init_pkru); | |
197 | return count; | |
198 | } | |
199 | ||
200 | static const struct file_operations fops_init_pkru = { | |
201 | .read = init_pkru_read_file, | |
202 | .write = init_pkru_write_file, | |
203 | .llseek = default_llseek, | |
204 | }; | |
205 | ||
206 | static int __init create_init_pkru_value(void) | |
207 | { | |
208 | debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR, | |
209 | arch_debugfs_dir, NULL, &fops_init_pkru); | |
210 | return 0; | |
211 | } | |
212 | late_initcall(create_init_pkru_value); | |
213 | ||
214 | static __init int setup_init_pkru(char *opt) | |
215 | { | |
216 | u32 new_init_pkru; | |
217 | ||
218 | if (kstrtouint(opt, 0, &new_init_pkru)) | |
219 | return 1; | |
220 | ||
221 | WRITE_ONCE(init_pkru_value, new_init_pkru); | |
222 | ||
223 | return 1; | |
224 | } | |
225 | __setup("init_pkru=", setup_init_pkru); |