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Diffstat (limited to 'sandbox/win/src/sidestep/preamble_patcher.h')
| -rw-r--r-- | sandbox/win/src/sidestep/preamble_patcher.h | 109 |
1 files changed, 109 insertions, 0 deletions
diff --git a/sandbox/win/src/sidestep/preamble_patcher.h b/sandbox/win/src/sidestep/preamble_patcher.h new file mode 100644 index 0000000..18cf7f8 --- /dev/null +++ b/sandbox/win/src/sidestep/preamble_patcher.h @@ -0,0 +1,109 @@ +// Copyright (c) 2012 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +// Definition of PreamblePatcher + +#ifndef SANDBOX_SRC_SIDESTEP_PREAMBLE_PATCHER_H__ +#define SANDBOX_SRC_SIDESTEP_PREAMBLE_PATCHER_H__ + +namespace sidestep { + +// Maximum size of the preamble stub. We overwrite at least the first 5 +// bytes of the function. Considering the worst case scenario, we need 4 +// bytes + the max instruction size + 5 more bytes for our jump back to +// the original code. With that in mind, 32 is a good number :) +const size_t kMaxPreambleStubSize = 32; + +// Possible results of patching/unpatching +enum SideStepError { + SIDESTEP_SUCCESS = 0, + SIDESTEP_INVALID_PARAMETER, + SIDESTEP_INSUFFICIENT_BUFFER, + SIDESTEP_JUMP_INSTRUCTION, + SIDESTEP_FUNCTION_TOO_SMALL, + SIDESTEP_UNSUPPORTED_INSTRUCTION, + SIDESTEP_NO_SUCH_MODULE, + SIDESTEP_NO_SUCH_FUNCTION, + SIDESTEP_ACCESS_DENIED, + SIDESTEP_UNEXPECTED, +}; + +// Implements a patching mechanism that overwrites the first few bytes of +// a function preamble with a jump to our hook function, which is then +// able to call the original function via a specially-made preamble-stub +// that imitates the action of the original preamble. +// +// Note that there are a number of ways that this method of patching can +// fail. The most common are: +// - If there is a jump (jxx) instruction in the first 5 bytes of +// the function being patched, we cannot patch it because in the +// current implementation we do not know how to rewrite relative +// jumps after relocating them to the preamble-stub. Note that +// if you really really need to patch a function like this, it +// would be possible to add this functionality (but at some cost). +// - If there is a return (ret) instruction in the first 5 bytes +// we cannot patch the function because it may not be long enough +// for the jmp instruction we use to inject our patch. +// - If there is another thread currently executing within the bytes +// that are copied to the preamble stub, it will crash in an undefined +// way. +// +// If you get any other error than the above, you're either pointing the +// patcher at an invalid instruction (e.g. into the middle of a multi- +// byte instruction, or not at memory containing executable instructions) +// or, there may be a bug in the disassembler we use to find +// instruction boundaries. +class PreamblePatcher { + public: + // Patches target_function to point to replacement_function using a provided + // preamble_stub of stub_size bytes. + // Returns An error code indicating the result of patching. + template <class T> + static SideStepError Patch(T target_function, T replacement_function, + void* preamble_stub, size_t stub_size) { + return RawPatchWithStub(target_function, replacement_function, + reinterpret_cast<unsigned char*>(preamble_stub), + stub_size, NULL); + } + + private: + + // Patches a function by overwriting its first few bytes with + // a jump to a different function. This is similar to the RawPatch + // function except that it uses the stub allocated by the caller + // instead of allocating it. + // + // To use this function, you first have to call VirtualProtect to make the + // target function writable at least for the duration of the call. + // + // target_function: A pointer to the function that should be + // patched. + // + // replacement_function: A pointer to the function that should + // replace the target function. The replacement function must have + // exactly the same calling convention and parameters as the original + // function. + // + // preamble_stub: A pointer to a buffer where the preamble stub + // should be copied. The size of the buffer should be sufficient to + // hold the preamble bytes. + // + // stub_size: Size in bytes of the buffer allocated for the + // preamble_stub + // + // bytes_needed: Pointer to a variable that receives the minimum + // number of bytes required for the stub. Can be set to NULL if you're + // not interested. + // + // Returns An error code indicating the result of patching. + static SideStepError RawPatchWithStub(void* target_function, + void *replacement_function, + unsigned char* preamble_stub, + size_t stub_size, + size_t* bytes_needed); +}; + +}; // namespace sidestep + +#endif // SANDBOX_SRC_SIDESTEP_PREAMBLE_PATCHER_H__ |