diff options
Diffstat (limited to 'arch/x86/mm/pkeys.c')
| -rw-r--r-- | arch/x86/mm/pkeys.c | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c new file mode 100644 index 0000000000..7418c367e3 --- /dev/null +++ b/arch/x86/mm/pkeys.c @@ -0,0 +1,197 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Intel Memory Protection Keys management + * Copyright (c) 2015, Intel Corporation. + */ +#include <linux/debugfs.h> /* debugfs_create_u32() */ +#include <linux/mm_types.h> /* mm_struct, vma, etc... */ +#include <linux/pkeys.h> /* PKEY_* */ +#include <uapi/asm-generic/mman-common.h> + +#include <asm/cpufeature.h> /* boot_cpu_has, ... */ +#include <asm/mmu_context.h> /* vma_pkey() */ + +int __execute_only_pkey(struct mm_struct *mm) +{ + bool need_to_set_mm_pkey = false; + int execute_only_pkey = mm->context.execute_only_pkey; + int ret; + + /* Do we need to assign a pkey for mm's execute-only maps? */ + if (execute_only_pkey == -1) { + /* Go allocate one to use, which might fail */ + execute_only_pkey = mm_pkey_alloc(mm); + if (execute_only_pkey < 0) + return -1; + need_to_set_mm_pkey = true; + } + + /* + * We do not want to go through the relatively costly + * dance to set PKRU if we do not need to. Check it + * first and assume that if the execute-only pkey is + * write-disabled that we do not have to set it + * ourselves. + */ + if (!need_to_set_mm_pkey && + !__pkru_allows_read(read_pkru(), execute_only_pkey)) { + return execute_only_pkey; + } + + /* + * Set up PKRU so that it denies access for everything + * other than execution. + */ + ret = arch_set_user_pkey_access(current, execute_only_pkey, + PKEY_DISABLE_ACCESS); + /* + * If the PKRU-set operation failed somehow, just return + * 0 and effectively disable execute-only support. + */ + if (ret) { + mm_set_pkey_free(mm, execute_only_pkey); + return -1; + } + + /* We got one, store it and use it from here on out */ + if (need_to_set_mm_pkey) + mm->context.execute_only_pkey = execute_only_pkey; + return execute_only_pkey; +} + +static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma) +{ + /* Do this check first since the vm_flags should be hot */ + if ((vma->vm_flags & VM_ACCESS_FLAGS) != VM_EXEC) + return false; + if (vma_pkey(vma) != vma->vm_mm->context.execute_only_pkey) + return false; + + return true; +} + +/* + * This is only called for *plain* mprotect calls. + */ +int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey) +{ + /* + * Is this an mprotect_pkey() call? If so, never + * override the value that came from the user. + */ + if (pkey != -1) + return pkey; + + /* + * The mapping is execute-only. Go try to get the + * execute-only protection key. If we fail to do that, + * fall through as if we do not have execute-only + * support in this mm. + */ + if (prot == PROT_EXEC) { + pkey = execute_only_pkey(vma->vm_mm); + if (pkey > 0) + return pkey; + } else if (vma_is_pkey_exec_only(vma)) { + /* + * Protections are *not* PROT_EXEC, but the mapping + * is using the exec-only pkey. This mapping was + * PROT_EXEC and will no longer be. Move back to + * the default pkey. + */ + return ARCH_DEFAULT_PKEY; + } + + /* + * This is a vanilla, non-pkey mprotect (or we failed to + * setup execute-only), inherit the pkey from the VMA we + * are working on. + */ + return vma_pkey(vma); +} + +#define PKRU_AD_MASK(pkey) (PKRU_AD_BIT << ((pkey) * PKRU_BITS_PER_PKEY)) + +/* + * Make the default PKRU value (at execve() time) as restrictive + * as possible. This ensures that any threads clone()'d early + * in the process's lifetime will not accidentally get access + * to data which is pkey-protected later on. + */ +u32 init_pkru_value = PKRU_AD_MASK( 1) | PKRU_AD_MASK( 2) | + PKRU_AD_MASK( 3) | PKRU_AD_MASK( 4) | + PKRU_AD_MASK( 5) | PKRU_AD_MASK( 6) | + PKRU_AD_MASK( 7) | PKRU_AD_MASK( 8) | + PKRU_AD_MASK( 9) | PKRU_AD_MASK(10) | + PKRU_AD_MASK(11) | PKRU_AD_MASK(12) | + PKRU_AD_MASK(13) | PKRU_AD_MASK(14) | + PKRU_AD_MASK(15); + +static ssize_t init_pkru_read_file(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + char buf[32]; + unsigned int len; + + len = sprintf(buf, "0x%x\n", init_pkru_value); + return simple_read_from_buffer(user_buf, count, ppos, buf, len); +} + +static ssize_t init_pkru_write_file(struct file *file, + const char __user *user_buf, size_t count, loff_t *ppos) +{ + char buf[32]; + ssize_t len; + u32 new_init_pkru; + + len = min(count, sizeof(buf) - 1); + if (copy_from_user(buf, user_buf, len)) + return -EFAULT; + + /* Make the buffer a valid string that we can not overrun */ + buf[len] = '\0'; + if (kstrtouint(buf, 0, &new_init_pkru)) + return -EINVAL; + + /* + * Don't allow insane settings that will blow the system + * up immediately if someone attempts to disable access + * or writes to pkey 0. + */ + if (new_init_pkru & (PKRU_AD_BIT|PKRU_WD_BIT)) + return -EINVAL; + + WRITE_ONCE(init_pkru_value, new_init_pkru); + return count; +} + +static const struct file_operations fops_init_pkru = { + .read = init_pkru_read_file, + .write = init_pkru_write_file, + .llseek = default_llseek, +}; + +static int __init create_init_pkru_value(void) +{ + /* Do not expose the file if pkeys are not supported. */ + if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) + return 0; + + debugfs_create_file("init_pkru", S_IRUSR | S_IWUSR, + arch_debugfs_dir, NULL, &fops_init_pkru); + return 0; +} +late_initcall(create_init_pkru_value); + +static __init int setup_init_pkru(char *opt) +{ + u32 new_init_pkru; + + if (kstrtouint(opt, 0, &new_init_pkru)) + return 1; + + WRITE_ONCE(init_pkru_value, new_init_pkru); + + return 1; +} +__setup("init_pkru=", setup_init_pkru); |