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 #include <asm/fpu/internal.h> /* init_fpstate */ 14 15 int __execute_only_pkey(struct mm_struct *mm) 16 { 17 bool need_to_set_mm_pkey = false; 18 int execute_only_pkey = mm->context.execute_only_pkey; 19 int ret; 20 21 /* Do we need to assign a pkey for mm's execute-only maps? */ 22 if (execute_only_pkey == -1) { 23 /* Go allocate one to use, which might fail */ 24 execute_only_pkey = mm_pkey_alloc(mm); 25 if (execute_only_pkey < 0) 26 return -1; 27 need_to_set_mm_pkey = true; 28 } 29 30 /* 31 * We do not want to go through the relatively costly 32 * dance to set PKRU if we do not need to. Check it 33 * first and assume that if the execute-only pkey is 34 * write-disabled that we do not have to set it 35 * ourselves. 36 */ 37 if (!need_to_set_mm_pkey && 38 !__pkru_allows_read(read_pkru(), execute_only_pkey)) { 39 return execute_only_pkey; 40 } 41 42 /* 43 * Set up PKRU so that it denies access for everything 44 * other than execution. 45 */ 46 ret = arch_set_user_pkey_access(current, execute_only_pkey, 47 PKEY_DISABLE_ACCESS); 48 /* 49 * If the PKRU-set operation failed somehow, just return 50 * 0 and effectively disable execute-only support. 51 */ 52 if (ret) { 53 mm_set_pkey_free(mm, execute_only_pkey); 54 return -1; 55 } 56 57 /* We got one, store it and use it from here on out */ 58 if (need_to_set_mm_pkey) 59 mm->context.execute_only_pkey = execute_only_pkey; 60 return execute_only_pkey; 61 } 62 63 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma) 64 { 65 /* Do this check first since the vm_flags should be hot */ 66 if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC) 67 return false; 68 if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey) 69 return false; 70 71 return true; 72 } 73 74 /* 75 * This is only called for *plain* mprotect calls. 76 */ 77 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey) 78 { 79 /* 80 * Is this an mprotect_pkey() call? If so, never 81 * override the value that came from the user. 82 */ 83 if (pkey != -1) 84 return pkey; 85 86 /* 87 * The mapping is execute-only. Go try to get the 88 * execute-only protection key. If we fail to do that, 89 * fall through as if we do not have execute-only 90 * support in this mm. 91 */ 92 if (prot == PROT_EXEC) { 93 pkey = execute_only_pkey(vma->vm_mm); 94 if (pkey > 0) 95 return pkey; 96 } else if (vma_is_pkey_exec_only(vma)) { 97 /* 98 * Protections are *not* PROT_EXEC, but the mapping 99 * is using the exec-only pkey. This mapping was 100 * PROT_EXEC and will no longer be. Move back to 101 * the default pkey. 102 */ 103 return ARCH_DEFAULT_PKEY; 104 } 105 106 /* 107 * This is a vanilla, non-pkey mprotect (or we failed to 108 * setup execute-only), inherit the pkey from the VMA we 109 * are working on. 110 */ 111 return vma_pkey(vma); 112 } 113 114 #define PKRU_AD_KEY(pkey) (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY)) 115 116 /* 117 * Make the default PKRU value (at execve() time) as restrictive 118 * as possible. This ensures that any threads clone()'d early 119 * in the process's lifetime will not accidentally get access 120 * to data which is pkey-protected later on. 121 */ 122 u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) | 123 PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) | 124 PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) | 125 PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) | 126 PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15); 127 128 /* 129 * Called from the FPU code when creating a fresh set of FPU 130 * registers. This is called from a very specific context where 131 * we know the FPU registers are safe for use and we can use PKRU 132 * directly. 133 */ 134 void copy_init_pkru_to_fpregs(void) 135 { 136 u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value); 137 /* 138 * Override the PKRU state that came from 'init_fpstate' 139 * with the baseline from the process. 140 */ 141 write_pkru(init_pkru_value_snapshot); 142 } 143 144 static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf, 145 size_t count, loff_t *ppos) 146 { 147 char buf[32]; 148 unsigned int len; 149 150 len = sprintf(buf, "0x%x\n", init_pkru_value); 151 return simple_read_from_buffer(user_buf, count, ppos, buf, len); 152 } 153 154 static ssize_t init_pkru_write_file(struct file *file, 155 const char __user *user_buf, size_t count, loff_t *ppos) 156 { 157 struct pkru_state *pk; 158 char buf[32]; 159 ssize_t len; 160 u32 new_init_pkru; 161 162 len = min(count, sizeof(buf) - 1); 163 if (copy_from_user(buf, user_buf, len)) 164 return -EFAULT; 165 166 /* Make the buffer a valid string that we can not overrun */ 167 buf[len] = '\0'; 168 if (kstrtouint(buf, 0, &new_init_pkru)) 169 return -EINVAL; 170 171 /* 172 * Don't allow insane settings that will blow the system 173 * up immediately if someone attempts to disable access 174 * or writes to pkey 0. 175 */ 176 if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT)) 177 return -EINVAL; 178 179 WRITE_ONCE(init_pkru_value, new_init_pkru); 180 pk = get_xsave_addr(&init_fpstate.xsave, XFEATURE_PKRU); 181 if (!pk) 182 return -EINVAL; 183 pk->pkru = new_init_pkru; 184 return count; 185 } 186 187 static const struct file_operations fops_init_pkru = { 188 .read = init_pkru_read_file, 189 .write = init_pkru_write_file, 190 .llseek = default_llseek, 191 }; 192 193 static int __init create_init_pkru_value(void) 194 { 195 debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR, 196 arch_debugfs_dir, NULL, &fops_init_pkru); 197 return 0; 198 } 199 late_initcall(create_init_pkru_value); 200 201 static __init int setup_init_pkru(char *opt) 202 { 203 u32 new_init_pkru; 204 205 if (kstrtouint(opt, 0, &new_init_pkru)) 206 return 1; 207 208 WRITE_ONCE(init_pkru_value, new_init_pkru); 209 210 return 1; 211 } 212 __setup("init_pkru=", setup_init_pkru); 213