cregit-Linux how code gets into the kernel

Release 4.7 arch/x86/mm/pkeys.c

Directory: arch/x86/mm
/*
 * 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/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()                   */
#include <asm/fpu/internal.h>           /* fpregs_active()              */


int __execute_only_pkey(struct mm_struct *mm) { int ret; /* * 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 (fpregs_active() && !__pkru_allows_read(read_pkru(), PKEY_DEDICATED_EXECUTE_ONLY)) { preempt_enable(); return PKEY_DEDICATED_EXECUTE_ONLY; } preempt_enable(); ret = arch_set_user_pkey_access(current, PKEY_DEDICATED_EXECUTE_ONLY, PKEY_DISABLE_ACCESS); /* * If the PKRU-set operation failed somehow, just return * 0 and effectively disable execute-only support. */ if (ret) return 0; return PKEY_DEDICATED_EXECUTE_ONLY; }

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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) != PKEY_DEDICATED_EXECUTE_ONLY) return false; return true; }

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/* * 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); }

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Directory: arch/x86/mm
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