1 /* 2 * Copyright (C) 2013 Google Inc. All rights reserved. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: 7 * 8 * * Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * * Redistributions in binary form must reproduce the above 11 * copyright notice, this list of conditions and the following disclaimer 12 * in the documentation and/or other materials provided with the 13 * distribution. 14 * * Neither the name of Google Inc. nor the names of its 15 * contributors may be used to endorse or promote products derived from 16 * this software without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 19 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 20 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 21 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 22 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 23 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 24 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 28 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 29 */ 30 31 #ifndef WTF_PageAllocator_h 32 #define WTF_PageAllocator_h 33 34 namespace WTF { 35 36 // Our granulatity of page allocation is 64KB. This is a Windows limitation, 37 // but we apply the same requirement for all platforms in order to keep 38 // things simple and consistent. 39 // We term these 64KB allocations "super pages". They're just a clump of 40 // underlying 4KB system pages. 41 static const size_t kSuperPageSize = 1 << 16; // 64KB 42 static const size_t kSuperPageOffsetMask = kSuperPageSize - 1; 43 static const size_t kSuperPageBaseMask = ~kSuperPageOffsetMask; 44 45 // All Blink-supported systems have 4096 sized system pages and can handle 46 // permissions and commit / decommit at this granularity. 47 static const size_t kSystemPageSize = 4096; 48 static const size_t kSystemPageOffsetMask = kSystemPageSize - 1; 49 50 static const size_t kNumSystemPagesPerSuperPage = kSuperPageSize / kSystemPageSize; 51 52 // Allocate one or more super pages. Addresses in the range will be readable and 53 // writeable but not executable. 54 // The requested address is just a hint; the actual address returned may 55 // differ. The returned address will be aligned to kSuperPageSize. 56 // len is in bytes, and must be a multiple of kSuperPageSize. 57 // This call will exit the process if the allocation cannot be satisfied. 58 void* allocSuperPages(void* addr, size_t len); 59 60 // Free one or more super pages. 61 // addr and len must match a previous call to allocPages(). 62 void freeSuperPages(void* addr, size_t len); 63 64 // Mark one or more system pages as being inaccessible. This is not reversible. 65 // Subsequently accessing any address in the range will fault, the addresses 66 // will not be re-used by future allocations. 67 // len must be a multiple of kSystemPageSize bytes. 68 void setSystemPagesInaccessible(void* addr, size_t len); 69 70 // Decommit one or more system pages. Decommitted means that the physical memory 71 // is released to the system, but the virtual address space remains reserved. 72 // System pages are re-committed by writing to them. 73 // Clients should not make any assumptions about the contents of decommitted 74 // system pages, before or after they write to the page. The only guarantee 75 // provided is that the contents of the system page will be deterministic again // after writing to it. In particlar note that system pages are not guaranteed 76 // to be zero-filled upon re-commit. 77 // len must be a multiple of kSystemPageSize bytes. 78 void decommitSystemPages(void* addr, size_t len); 79 80 // Returns a suitable pointer for starting to allocate super pages. 81 // The pointer is not guaranteed to be "unused", but does represent an address 82 // that has a good chance of being unused. The pointer is also randomized to 83 // provide reasonable ASLR. 84 char* getRandomSuperPageBase(); 85 86 } // namespace WTF 87 88 #endif // WTF_PageAllocator_h 89
