LXR linux/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
  14int __execute_only_pkey(struct mm_struct *mm)
  15{
  16        bool need_to_set_mm_pkey = false;
  17        int execute_only_pkey = mm->context.execute_only_pkey;
  18        int ret;
  19
  20        /* Do we need to assign a pkey for mm's execute-only maps? */
  21        if (execute_only_pkey == -1) {
  22                /* Go allocate one to use, which might fail */
  23                execute_only_pkey = mm_pkey_alloc(mm);
  24                if (execute_only_pkey < 0)
  25                        return -1;
  26                need_to_set_mm_pkey = true;
  27        }
  28
  29        /*
  30         * We do not want to go through the relatively costly
  31         * dance to set PKRU if we do not need to.  Check it
  32         * first and assume that if the execute-only pkey is
  33         * write-disabled that we do not have to set it
  34         * ourselves.
  35         */
  36        if (!need_to_set_mm_pkey &&
  37            !__pkru_allows_read(read_pkru(), execute_only_pkey)) {
  38                return execute_only_pkey;
  39        }
  40
  41        /*
  42         * Set up PKRU so that it denies access for everything
  43         * other than execution.
  44         */
  45        ret = arch_set_user_pkey_access(current, execute_only_pkey,
  46                        PKEY_DISABLE_ACCESS);
  47        /*
  48         * If the PKRU-set operation failed somehow, just return
  49         * 0 and effectively disable execute-only support.
  50         */
  51        if (ret) {
  52                mm_set_pkey_free(mm, execute_only_pkey);
  53                return -1;
  54        }
  55
  56        /* We got one, store it and use it from here on out */
  57        if (need_to_set_mm_pkey)
  58                mm->context.execute_only_pkey = execute_only_pkey;
  59        return execute_only_pkey;
  60}
  61
  62static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
  63{
  64        /* Do this check first since the vm_flags should be hot */
  65        if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC)
  66                return false;
  67        if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey)
  68                return false;
  69
  70        return true;
  71}
  72
  73/*
  74 * This is only called for *plain* mprotect calls.
  75 */
  76int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey)
  77{
  78        /*
  79         * Is this an mprotect_pkey() call?  If so, never
  80         * override the value that came from the user.
  81         */
  82        if (pkey != -1)
  83                return pkey;
  84
  85        /*
  86         * The mapping is execute-only.  Go try to get the
  87         * execute-only protection key.  If we fail to do that,
  88         * fall through as if we do not have execute-only
  89         * support in this mm.
  90         */
  91        if (prot == PROT_EXEC) {
  92                pkey = execute_only_pkey(vma->vm_mm);
  93                if (pkey > 0)
  94                        return pkey;
  95        } else if (vma_is_pkey_exec_only(vma)) {
  96                /*
  97                 * Protections are *not* PROT_EXEC, but the mapping
  98                 * is using the exec-only pkey.  This mapping was
  99                 * PROT_EXEC and will no longer be.  Move back to
 100                 * the default pkey.
 101                 */
 102                return ARCH_DEFAULT_PKEY;
 103        }
 104
 105        /*
 106         * This is a vanilla, non-pkey mprotect (or we failed to
 107         * setup execute-only), inherit the pkey from the VMA we
 108         * are working on.
 109         */
 110        return vma_pkey(vma);
 111}
 112
 113#define PKRU_AD_KEY(pkey)       (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY))
 114
 115/*
 116 * Make the default PKRU value (at execve() time) as restrictive
 117 * as possible.  This ensures that any threads clone()'d early
 118 * in the process's lifetime will not accidentally get access
 119 * to data which is pkey-protected later on.
 120 */
 121u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
 122                      PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) |
 123                      PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) |
 124                      PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) |
 125                      PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15);
 126
 127static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf,
 128                             size_t count, loff_t *ppos)
 129{
 130        char buf[32];
 131        unsigned int len;
 132
 133        len = sprintf(buf, "0x%x\n", init_pkru_value);
 134        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 135}
 136
 137static ssize_t init_pkru_write_file(struct file *file,
 138                 const char __user *user_buf, size_t count, loff_t *ppos)
 139{
 140        char buf[32];
 141        ssize_t len;
 142        u32 new_init_pkru;
 143
 144        len = min(count, sizeof(buf) - 1);
 145        if (copy_from_user(buf, user_buf, len))
 146                return -EFAULT;
 147
 148        /* Make the buffer a valid string that we can not overrun */
 149        buf[len] = '\0';
 150        if (kstrtouint(buf, 0, &new_init_pkru))
 151                return -EINVAL;
 152
 153        /*
 154         * Don't allow insane settings that will blow the system
 155         * up immediately if someone attempts to disable access
 156         * or writes to pkey 0.
 157         */
 158        if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT))
 159                return -EINVAL;
 160
 161        WRITE_ONCE(init_pkru_value, new_init_pkru);
 162        return count;
 163}
 164
 165static const struct file_operations fops_init_pkru = {
 166        .read = init_pkru_read_file,
 167        .write = init_pkru_write_file,
 168        .llseek = default_llseek,
 169};
 170
 171static int __init create_init_pkru_value(void)
 172{
 173        /* Do not expose the file if pkeys are not supported. */
 174        if (!cpu_feature_enabled(X86_FEATURE_OSPKE))
 175                return 0;
 176
 177        debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR,
 178                        arch_debugfs_dir, NULL, &fops_init_pkru);
 179        return 0;
 180}
 181late_initcall(create_init_pkru_value);
 182
 183static __init int setup_init_pkru(char *opt)
 184{
 185        u32 new_init_pkru;
 186
 187        if (kstrtouint(opt, 0, &new_init_pkru))
 188                return 1;
 189
 190        WRITE_ONCE(init_pkru_value, new_init_pkru);
 191
 192        return 1;
 193}
 194__setup("init_pkru=", setup_init_pkru);
 195