arch/x86/mm/pkeys.c

   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 regstiers 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);