| //===-- protected_pages.h -------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // This file provides protected pages that fault when accessing prior or past |
| // it. This is useful to check memory functions that must not access outside of |
| // the provided size limited buffer. |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LIBC_TEST_SRC_STRING_MEMORY_UTILS_PROTECTED_PAGES_H |
| #define LIBC_TEST_SRC_STRING_MEMORY_UTILS_PROTECTED_PAGES_H |
| |
| #include "src/__support/macros/properties/os.h" // LIBC_TARGET_OS_IS_LINUX |
| #if defined(LIBC_FULL_BUILD) || !defined(LIBC_TARGET_OS_IS_LINUX) |
| #error "Protected pages requires mmap and cannot be used in full build mode." |
| #endif // defined(LIBC_FULL_BUILD) || !defined(LIBC_TARGET_OS_IS_LINUX) |
| |
| #include "src/__support/macros/attributes.h" // LIBC_INLINE |
| #include <stddef.h> // size_t |
| #include <stdint.h> // uint8_t |
| #include <sys/mman.h> // mmap, munmap |
| #include <unistd.h> // sysconf, _SC_PAGESIZE |
| |
| // Returns mmap page size. |
| LIBC_INLINE size_t GetPageSize() { |
| static const size_t PAGE_SIZE = sysconf(_SC_PAGESIZE); |
| return PAGE_SIZE; |
| } |
| |
| // Represents a page of memory whose access can be configured throught the |
| // 'WithAccess' function. Accessing data above or below this page will trap as |
| // it is sandwiched between two pages with no read / write access. |
| struct Page { |
| // Returns an aligned pointer that can be accessed up to page_size. Accessing |
| // data at ptr[-1] will fault. |
| LIBC_INLINE uint8_t *bottom(size_t size) const { |
| if (size >= page_size) |
| __builtin_trap(); |
| return page_ptr; |
| } |
| // Returns a pointer to a buffer that can be accessed up to size. Accessing |
| // data at ptr[size] will trap. |
| LIBC_INLINE uint8_t *top(size_t size) const { |
| return page_ptr + page_size - size; |
| } |
| |
| // protection is one of PROT_READ / PROT_WRITE. |
| LIBC_INLINE Page &WithAccess(int protection) { |
| if (mprotect(page_ptr, page_size, protection) != 0) |
| __builtin_trap(); |
| return *this; |
| } |
| |
| const size_t page_size; |
| uint8_t *const page_ptr; |
| }; |
| |
| // Allocates 5 consecutive pages that will trap if accessed. |
| // | page layout | access | page name | |
| // |-------------|--------|:---------:| |
| // | 0 | trap | | |
| // | 1 | custom | A | |
| // | 2 | trap | | |
| // | 3 | custom | B | |
| // | 4 | trap | | |
| // |
| // The pages A and B can be retrieved as with 'GetPageA' / 'GetPageB' and their |
| // accesses can be customized through the 'WithAccess' function. |
| struct ProtectedPages { |
| static constexpr size_t PAGES = 5; |
| |
| ProtectedPages() |
| : page_size(GetPageSize()), |
| ptr(mmap(/*address*/ nullptr, /*length*/ PAGES * page_size, |
| /*protection*/ PROT_NONE, |
| /*flags*/ MAP_PRIVATE | MAP_ANONYMOUS, /*fd*/ -1, |
| /*offset*/ 0)) { |
| if (reinterpret_cast<intptr_t>(ptr) == -1) |
| __builtin_trap(); |
| } |
| ~ProtectedPages() { munmap(ptr, PAGES * page_size); } |
| |
| LIBC_INLINE Page GetPageA() const { return Page{page_size, page<1>()}; } |
| LIBC_INLINE Page GetPageB() const { return Page{page_size, page<3>()}; } |
| |
| private: |
| template <size_t index> LIBC_INLINE uint8_t *page() const { |
| static_assert(index < PAGES); |
| return static_cast<uint8_t *>(ptr) + (index * page_size); |
| } |
| |
| const size_t page_size; |
| void *const ptr = nullptr; |
| }; |
| |
| #endif // LIBC_TEST_SRC_STRING_MEMORY_UTILS_PROTECTED_PAGES_H |