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/*
* Intel Memory Protection Keys management
* Copyright (c) 2015, Intel Corporation.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms and conditions of the GNU General Public License,
* version 2, as published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*/
#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. We need preempt off so that nobody
* can make fpregs inactive.
*/
preempt_disable();
if (!need_to_set_mm_pkey &&
current->thread.fpu.initialized &&
!__pkru_allows_read(read_pkru(), execute_only_pkey)) {
preempt_enable();
return execute_only_pkey;
}
preempt_enable();
/*
* 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_READ | VM_WRITE | VM_EXEC)) != 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;
/*
* Look for a protection-key-drive execute-only mapping
* which is now being given permissions that are not
* execute-only. Move it back to the default pkey.
*/
if (vma_is_pkey_exec_only(vma) &&
(prot & (PROT_READ|PROT_WRITE))) {
return 0;
}
/*
* 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.
*/
if (prot == PROT_EXEC) {
pkey = execute_only_pkey(vma->vm_mm);
if (pkey > 0)
return 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_KEY(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_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
PKRU_AD_KEY( 4) | PKRU_AD_KEY( 5) | PKRU_AD_KEY( 6) |
PKRU_AD_KEY( 7) | PKRU_AD_KEY( 8) | PKRU_AD_KEY( 9) |
PKRU_AD_KEY(10) | PKRU_AD_KEY(11) | PKRU_AD_KEY(12) |
PKRU_AD_KEY(13) | PKRU_AD_KEY(14) | PKRU_AD_KEY(15);
/*
* Called from the FPU code when creating a fresh set of FPU
* registers. This is called from a very specific context where
* we know the FPU regstiers are safe for use and we can use PKRU
* directly.
*/
void copy_init_pkru_to_fpregs(void)
{
u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value);
/*
* Any write to PKRU takes it out of the XSAVE 'init
* state' which increases context switch cost. Avoid
* writing 0 when PKRU was already 0.
*/
if (!init_pkru_value_snapshot && !read_pkru())
return;
/*
* Override the PKRU state that came from 'init_fpstate'
* with the baseline from the process.
*/
write_pkru(init_pkru_value_snapshot);
}
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)
{
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);
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