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+/*
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+ * Intel Memory Protection Keys management
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+ * Copyright (c) 2015, Intel Corporation.
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+ *
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+ * This program is free software; you can redistribute it and/or modify it
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+ * under the terms and conditions of the GNU General Public License,
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+ * version 2, as published by the Free Software Foundation.
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+ *
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+ * This program is distributed in the hope it will be useful, but WITHOUT
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+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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+ * more details.
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+ */
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+#include <linux/mm_types.h> /* mm_struct, vma, etc... */
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+#include <linux/pkeys.h> /* PKEY_* */
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+#include <uapi/asm-generic/mman-common.h>
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+
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+#include <asm/cpufeature.h> /* boot_cpu_has, ... */
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+#include <asm/mmu_context.h> /* vma_pkey() */
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+#include <asm/fpu/internal.h> /* fpregs_active() */
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+
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+int __execute_only_pkey(struct mm_struct *mm)
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+{
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+ int ret;
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+
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+ /*
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+ * We do not want to go through the relatively costly
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+ * dance to set PKRU if we do not need to. Check it
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+ * first and assume that if the execute-only pkey is
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+ * write-disabled that we do not have to set it
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+ * ourselves. We need preempt off so that nobody
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+ * can make fpregs inactive.
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+ */
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+ preempt_disable();
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+ if (fpregs_active() &&
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+ !__pkru_allows_read(read_pkru(), PKEY_DEDICATED_EXECUTE_ONLY)) {
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+ preempt_enable();
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+ return PKEY_DEDICATED_EXECUTE_ONLY;
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+ }
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+ preempt_enable();
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+ ret = arch_set_user_pkey_access(current, PKEY_DEDICATED_EXECUTE_ONLY,
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+ PKEY_DISABLE_ACCESS);
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+ /*
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+ * If the PKRU-set operation failed somehow, just return
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+ * 0 and effectively disable execute-only support.
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+ */
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+ if (ret)
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+ return 0;
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+
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+ return PKEY_DEDICATED_EXECUTE_ONLY;
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+}
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+
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+static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
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+{
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+ /* Do this check first since the vm_flags should be hot */
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+ if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
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+ return false;
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+ if (vma_pkey(vma) != PKEY_DEDICATED_EXECUTE_ONLY)
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+ return false;
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+
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+ return true;
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+}
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+
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+/*
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+ * This is only called for *plain* mprotect calls.
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+ */
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+int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot, int pkey)
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+{
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+ /*
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+ * Is this an mprotect_pkey() call? If so, never
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+ * override the value that came from the user.
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+ */
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+ if (pkey != -1)
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+ return pkey;
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+ /*
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+ * Look for a protection-key-drive execute-only mapping
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+ * which is now being given permissions that are not
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+ * execute-only. Move it back to the default pkey.
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+ */
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+ if (vma_is_pkey_exec_only(vma) &&
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+ (prot & (PROT_READ|PROT_WRITE))) {
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+ return 0;
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+ }
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+ /*
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+ * The mapping is execute-only. Go try to get the
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+ * execute-only protection key. If we fail to do that,
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+ * fall through as if we do not have execute-only
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+ * support.
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+ */
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+ if (prot == PROT_EXEC) {
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+ pkey = execute_only_pkey(vma->vm_mm);
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+ if (pkey > 0)
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+ return pkey;
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+ }
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+ /*
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+ * This is a vanilla, non-pkey mprotect (or we failed to
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+ * setup execute-only), inherit the pkey from the VMA we
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+ * are working on.
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+ */
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+ return vma_pkey(vma);
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+}
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Dave Hansen