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 */ 14 #include <linux/debugfs.h> /* debugfs_create_u32() */ 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() */ 21 22 int __execute_only_pkey(struct mm_struct *mm) 23 { 24 bool need_to_set_mm_pkey = false; 25 int execute_only_pkey = mm->context.execute_only_pkey; 26 int ret; 27 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 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(); 46 if (!need_to_set_mm_pkey && 47 current->thread.fpu.initialized && 48 !__pkru_allows_read(read_pkru(), execute_only_pkey)) { 49 preempt_enable(); 50 return execute_only_pkey; 51 } 52 preempt_enable(); 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, 59 PKEY_DISABLE_ACCESS); 60 /* 61 * If the PKRU-set operation failed somehow, just return 62 * 0 and effectively disable execute-only support. 63 */ 64 if (ret) { 65 mm_set_pkey_free(mm, execute_only_pkey); 66 return -1; 67 } 68 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; 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; 80 if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey) 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 } 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 143 * directly. 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 } 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); 226