[libc-commits] [libc] [libc] Add fuzzers for `memcpy` and `memset` (PR #90591)

[Clement Courbet via libc-commits]

================
@@ -0,0 +1,86 @@
+//===-- 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_FUZZING_STRING_PROTECTED_PAGES_H
+#define LIBC_FUZZING_STRING_PROTECTED_PAGES_H
+
+#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.
+size_t GetPageSize() { return sysconf(_SC_PAGESIZE); }
+
+// Represents a page of memory which 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.
+  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 fault.
+  uint8_t *top(size_t size) const { return page_ptr + page_size - size; }
+
+  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 0 (FAULT)  |
+// | page 1 (CUSTOM) |
+// | page 2 (FAULT)  |
+// | page 3 (CUSTOM) |
----------------
legrosbuffle wrote:

page B

https://github.com/llvm/llvm-project/pull/90591