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 22 int __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 53 static 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 */ 67 int __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 } 102