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 #include <asm/fpu/internal.h>           /* fpregs_active()              */
  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.  We need preempt off so that nobody
  44          * can make fpregs inactive.
  45          */
  46         preempt_disable();
  47         if (!need_to_set_mm_pkey &&
  48             fpregs_active() &&
  49             !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
  50                 preempt_enable();
  51                 return execute_only_pkey;
  52         }
  53         preempt_enable();
  54
  55         /*
  56          * Set up PKRU so that it denies access for everything
  57          * other than execution.
  58          */
  59         ret = arch_set_user_pkey_access(current, execute_only_pkey,
  60                         PKEY_DISABLE_ACCESS);
  61         /*
  62          * If the PKRU-set operation failed somehow, just return
  63          * 0 and effectively disable execute-only support.
  64          */
  65         if (ret) {
  66                 mm_set_pkey_free(mm, execute_only_pkey);
  67                 return -1;
  68         }
  69
  70         /* We got one, store it and use it from here on out */
  71         if (need_to_set_mm_pkey)
  72                 mm->context.execute_only_pkey = execute_only_pkey;
  73         return execute_only_pkey;
  74 }
  75
  76 static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
  77 {
  78         /* Do this check first since the vm_flags should be hot */
  79         if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
  80                 return false;
  81         if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey)
  82                 return false;
  83
  84         return true;
  85 }
  86
  87 /*
  88  * This is only called for *plain* mprotect calls.
  89  */
  90 int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey)
  91 {
  92         /*
  93          * Is this an mprotect_pkey() call?  If so, never
  94          * override the value that came from the user.
  95          */
  96         if (pkey != -1)
  97                 return pkey;
  98         /*
  99          * Look for a protection-key-drive execute-only mapping
 100          * which is now being given permissions that are not
 101          * execute-only.  Move it back to the default pkey.
 102          */
 103         if (vma_is_pkey_exec_only(vma) &&
 104             (prot & (PROT_READ|PROT_WRITE))) {
 105                 return 0;
 106         }
 107         /*
 108          * The mapping is execute-only.  Go try to get the
 109          * execute-only protection key.  If we fail to do that,
 110          * fall through as if we do not have execute-only
 111          * support.
 112          */
 113         if (prot == PROT_EXEC) {
 114                 pkey = execute_only_pkey(vma->vm_mm);
 115                 if (pkey > 0)
 116                         return pkey;
 117         }
 118         /*
 119          * This is a vanilla, non-pkey mprotect (or we failed to
 120          * setup execute-only), inherit the pkey from the VMA we
 121          * are working on.
 122          */
 123         return vma_pkey(vma);
 124 }
 125
 126 #define PKRU_AD_KEY(pkey)       (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY))
 127
 128 /*
 129  * Make the default PKRU value (at execve() time) as restrictive
 130  * as possible.  This ensures that any threads clone()'d early
 131  * in the process's lifetime will not accidentally get access
 132  * to data which is pkey-protected later on.
 133  */
 134 u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
 135                       PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) |
 136                       PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) |
 137                       PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) |
 138                       PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15);
 139
 140 /*
 141  * Called from the FPU code when creating a fresh set of FPU
 142  * registers.  This is called from a very specific context where
 143  * we know the FPU regstiers are safe for use and we can use PKRU
 144  * directly.
 145  */
 146 void copy_init_pkru_to_fpregs(void)
 147 {
 148         u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value);
 149         /*
 150          * Any write to PKRU takes it out of the XSAVE 'init
 151          * state' which increases context switch cost.  Avoid
 152          * writing 0 when PKRU was already 0.
 153          */
 154         if (!init_pkru_value_snapshot && !read_pkru())
 155                 return;
 156         /*
 157          * Override the PKRU state that came from 'init_fpstate'
 158          * with the baseline from the process.
 159          */
 160         write_pkru(init_pkru_value_snapshot);
 161 }
 162
 163 static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf,
 164                              size_t count, loff_t *ppos)
 165 {
 166         char buf[32];
 167         unsigned int len;
 168
 169         len = sprintf(buf, "0x%x\n", init_pkru_value);
 170         return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 171 }
 172
 173 static ssize_t init_pkru_write_file(struct file *file,
 174                  const char __user *user_buf, size_t count, loff_t *ppos)
 175 {
 176         char buf[32];
 177         ssize_t len;
 178         u32 new_init_pkru;
 179
 180         len = min(count, sizeof(buf) - 1);
 181         if (copy_from_user(buf, user_buf, len))
 182                 return -EFAULT;
 183
 184         /* Make the buffer a valid string that we can not overrun */
 185         buf[len] = '\0';
 186         if (kstrtouint(buf, 0, &new_init_pkru))
 187                 return -EINVAL;
 188
 189         /*
 190          * Don't allow insane settings that will blow the system
 191          * up immediately if someone attempts to disable access
 192          * or writes to pkey 0.
 193          */
 194         if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT))
 195                 return -EINVAL;
 196
 197         WRITE_ONCE(init_pkru_value, new_init_pkru);
 198         return count;
 199 }
 200
 201 static const struct file_operations fops_init_pkru = {
 202         .read = init_pkru_read_file,
 203         .write = init_pkru_write_file,
 204         .llseek = default_llseek,
 205 };
 206
 207 static int __init create_init_pkru_value(void)
 208 {
 209         debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR,
 210                         arch_debugfs_dir, NULL, &fops_init_pkru);
 211         return 0;
 212 }
 213 late_initcall(create_init_pkru_value);
 214
 215 static __init int setup_init_pkru(char *opt)
 216 {
 217         u32 new_init_pkru;
 218
 219         if (kstrtouint(opt, 0, &new_init_pkru))
 220                 return 1;
 221
 222         WRITE_ONCE(init_pkru_value, new_init_pkru);
 223
 224         return 1;
 225 }
 226 __setup("init_pkru=", setup_init_pkru);