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/mm_types.h>             /* mm_struct, vma, etc...       */
 15#include <linux/pkeys.h>                /* PKEY_*                       */
 16#include <uapi/asm-generic/mman-common.h>
 17
 18#include <asm/cpufeature.h>             /* boot_cpu_has, ...            */
 19#include <asm/mmu_context.h>            /* vma_pkey()                   */
 20#include <asm/fpu/internal.h>           /* fpregs_active()              */
 21
 22int __execute_only_pkey(struct mm_struct *mm)
 23{
 24	int ret;
 25
 26	/*
 27	 * We do not want to go through the relatively costly
 28	 * dance to set PKRU if we do not need to.  Check it
 29	 * first and assume that if the execute-only pkey is
 30	 * write-disabled that we do not have to set it
 31	 * ourselves.  We need preempt off so that nobody
 32	 * can make fpregs inactive.
 33	 */
 34	preempt_disable();
 35	if (fpregs_active() &&
 36	    !__pkru_allows_read(read_pkru(), PKEY_DEDICATED_EXECUTE_ONLY)) {
 37		preempt_enable();
 38		return PKEY_DEDICATED_EXECUTE_ONLY;
 39	}
 40	preempt_enable();
 41	ret = arch_set_user_pkey_access(current, PKEY_DEDICATED_EXECUTE_ONLY,
 42			PKEY_DISABLE_ACCESS);
 43	/*
 44	 * If the PKRU-set operation failed somehow, just return
 45	 * 0 and effectively disable execute-only support.
 46	 */
 47	if (ret)
 48		return 0;
 49
 50	return PKEY_DEDICATED_EXECUTE_ONLY;
 51}
 52
 53static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
 54{
 55	/* Do this check first since the vm_flags should be hot */
 56	if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
 57		return false;
 58	if (vma_pkey(vma) != PKEY_DEDICATED_EXECUTE_ONLY)
 59		return false;
 60
 61	return true;
 62}
 63
 64/*
 65 * This is only called for *plain* mprotect calls.
 66 */
 67int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey)
 68{
 69	/*
 70	 * Is this an mprotect_pkey() call?  If so, never
 71	 * override the value that came from the user.
 72	 */
 73	if (pkey != -1)
 74		return pkey;
 75	/*
 76	 * Look for a protection-key-drive execute-only mapping
 77	 * which is now being given permissions that are not
 78	 * execute-only.  Move it back to the default pkey.
 79	 */
 80	if (vma_is_pkey_exec_only(vma) &&
 81	    (prot & (PROT_READ|PROT_WRITE))) {
 82		return 0;
 83	}
 84	/*
 85	 * The mapping is execute-only.  Go try to get the
 86	 * execute-only protection key.  If we fail to do that,
 87	 * fall through as if we do not have execute-only
 88	 * support.
 89	 */
 90	if (prot == PROT_EXEC) {
 91		pkey = execute_only_pkey(vma->vm_mm);
 92		if (pkey > 0)
 93			return pkey;
 94	}
 95	/*
 96	 * This is a vanilla, non-pkey mprotect (or we failed to
 97	 * setup execute-only), inherit the pkey from the VMA we
 98	 * are working on.
 99	 */
100	return vma_pkey(vma);
101}