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 #include <asm/fpu/internal.h> /* init_fpstate */ 22 23 int __execute_only_pkey(struct mm_struct *mm) 24 { 25 bool need_to_set_mm_pkey = false; 26 int execute_only_pkey = mm->context.execute_only_pkey; 27 int ret; 28 29 /* Do we need to assign a pkey for mm's execute-only maps? */ 30 if (execute_only_pkey == -1) { 31 /* Go allocate one to use, which might fail */ 32 execute_only_pkey = mm_pkey_alloc(mm); 33 if (execute_only_pkey < 0) 34 return -1; 35 need_to_set_mm_pkey = true; 36 } 37 38 /* 39 * We do not want to go through the relatively costly 40 * dance to set PKRU if we do not need to. Check it 41 * first and assume that if the execute-only pkey is 42 * write-disabled that we do not have to set it 43 * ourselves. 44 */ 45 if (!need_to_set_mm_pkey && 46 !__pkru_allows_read(read_pkru(), execute_only_pkey)) { 47 return execute_only_pkey; 48 } 49 50 /* 51 * Set up PKRU so that it denies access for everything 52 * other than execution. 53 */ 54 ret = arch_set_user_pkey_access(current, execute_only_pkey, 55 PKEY_DISABLE_ACCESS); 56 /* 57 * If the PKRU-set operation failed somehow, just return 58 * 0 and effectively disable execute-only support. 59 */ 60 if (ret) { 61 mm_set_pkey_free(mm, execute_only_pkey); 62 return -1; 63 } 64 65 /* We got one, store it and use it from here on out */ 66 if (need_to_set_mm_pkey) 67 mm->context.execute_only_pkey = execute_only_pkey; 68 return execute_only_pkey; 69 } 70 71 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma) 72 { 73 /* Do this check first since the vm_flags should be hot */ 74 if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC) 75 return false; 76 if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey) 77 return false; 78 79 return true; 80 } 81 82 /* 83 * This is only called for *plain* mprotect calls. 84 */ 85 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey) 86 { 87 /* 88 * Is this an mprotect_pkey() call? If so, never 89 * override the value that came from the user. 90 */ 91 if (pkey != -1) 92 return pkey; 93 94 /* 95 * The mapping is execute-only. Go try to get the 96 * execute-only protection key. If we fail to do that, 97 * fall through as if we do not have execute-only 98 * support in this mm. 99 */ 100 if (prot == PROT_EXEC) { 101 pkey = execute_only_pkey(vma->vm_mm); 102 if (pkey > 0) 103 return pkey; 104 } else if (vma_is_pkey_exec_only(vma)) { 105 /* 106 * Protections are *not* PROT_EXEC, but the mapping 107 * is using the exec-only pkey. This mapping was 108 * PROT_EXEC and will no longer be. Move back to 109 * the default pkey. 110 */ 111 return ARCH_DEFAULT_PKEY; 112 } 113 114 /* 115 * This is a vanilla, non-pkey mprotect (or we failed to 116 * setup execute-only), inherit the pkey from the VMA we 117 * are working on. 118 */ 119 return vma_pkey(vma); 120 } 121 122 #define PKRU_AD_KEY(pkey) (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY)) 123 124 /* 125 * Make the default PKRU value (at execve() time) as restrictive 126 * as possible. This ensures that any threads clone()'d early 127 * in the process's lifetime will not accidentally get access 128 * to data which is pkey-protected later on. 129 */ 130 u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) | 131 PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) | 132 PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) | 133 PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) | 134 PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15); 135 136 /* 137 * Called from the FPU code when creating a fresh set of FPU 138 * registers. This is called from a very specific context where 139 * we know the FPU regstiers are safe for use and we can use PKRU 140 * directly. 141 */ 142 void copy_init_pkru_to_fpregs(void) 143 { 144 u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value); 145 /* 146 * Override the PKRU state that came from 'init_fpstate' 147 * with the baseline from the process. 148 */ 149 write_pkru(init_pkru_value_snapshot); 150 } 151 152 static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf, 153 size_t count, loff_t *ppos) 154 { 155 char buf[32]; 156 unsigned int len; 157 158 len = sprintf(buf, "0x%x\n", init_pkru_value); 159 return simple_read_from_buffer(user_buf, count, ppos, buf, len); 160 } 161 162 static ssize_t init_pkru_write_file(struct file *file, 163 const char __user *user_buf, size_t count, loff_t *ppos) 164 { 165 struct pkru_state *pk; 166 char buf[32]; 167 ssize_t len; 168 u32 new_init_pkru; 169 170 len = min(count, sizeof(buf) - 1); 171 if (copy_from_user(buf, user_buf, len)) 172 return -EFAULT; 173 174 /* Make the buffer a valid string that we can not overrun */ 175 buf[len] = '\0'; 176 if (kstrtouint(buf, 0, &new_init_pkru)) 177 return -EINVAL; 178 179 /* 180 * Don't allow insane settings that will blow the system 181 * up immediately if someone attempts to disable access 182 * or writes to pkey 0. 183 */ 184 if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT)) 185 return -EINVAL; 186 187 WRITE_ONCE(init_pkru_value, new_init_pkru); 188 pk = get_xsave_addr(&init_fpstate.xsave, XFEATURE_PKRU); 189 if (!pk) 190 return -EINVAL; 191 pk->pkru = new_init_pkru; 192 return count; 193 } 194 195 static const struct file_operations fops_init_pkru = { 196 .read = init_pkru_read_file, 197 .write = init_pkru_write_file, 198 .llseek = default_llseek, 199 }; 200 201 static int __init create_init_pkru_value(void) 202 { 203 debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR, 204 arch_debugfs_dir, NULL, &fops_init_pkru); 205 return 0; 206 } 207 late_initcall(create_init_pkru_value); 208 209 static __init int setup_init_pkru(char *opt) 210 { 211 u32 new_init_pkru; 212 213 if (kstrtouint(opt, 0, &new_init_pkru)) 214 return 1; 215 216 WRITE_ONCE(init_pkru_value, new_init_pkru); 217 218 return 1; 219 } 220 __setup("init_pkru=", setup_init_pkru); 221