arch/x86/mm/pkeys.c

   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.fpstate_active &&
  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);