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Diffstat (limited to 'driver/sanitizer_hooks_with_pc.cpp')
| -rw-r--r-- | driver/sanitizer_hooks_with_pc.cpp | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/driver/sanitizer_hooks_with_pc.cpp b/driver/sanitizer_hooks_with_pc.cpp new file mode 100644 index 00000000..bb3ec5e1 --- /dev/null +++ b/driver/sanitizer_hooks_with_pc.cpp @@ -0,0 +1,187 @@ +// Copyright 2021 Code Intelligence GmbH +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +#include "sanitizer_hooks_with_pc.h" + +#include <cstddef> +#include <cstdint> + +// libFuzzer's compare hooks obtain the caller's address from the compiler +// builtin __builtin_return_adress. Since Java code will invoke the hooks always +// from the same native function, this builtin would always return the same +// value. Internally, the libFuzzer hooks call through to the always inlined +// HandleCmp and thus can't be mimicked without patching libFuzzer. +// +// We solve this problem via an inline assembly trampoline construction that +// translates a runtime argument `fake_pc` in the range [0, 512) into a call to +// a hook with a fake return address whose lower 9 bits are `fake_pc` up to a +// constant shift. This is achieved by pushing a return address pointing into +// 512 ret instructions at offset `fake_pc` onto the stack and then jumping +// directly to the address of the hook. +// +// Note: We only set the lowest 9 bits of the return address since only these +// bits are used by the libFuzzer value profiling mode for integer compares, see +// https://github.com/llvm/llvm-project/blob/704d92607d26e696daba596b72cb70effe79a872/compiler-rt/lib/fuzzer/FuzzerTracePC.cpp#L390 +// as well as +// https://github.com/llvm/llvm-project/blob/704d92607d26e696daba596b72cb70effe79a872/compiler-rt/lib/fuzzer/FuzzerValueBitMap.h#L34 +// ValueProfileMap.AddValue() truncates its argument to 16 bits and shifts the +// PC to the left by log_2(128)=7, which means that only the lowest 16 - 7 bits +// of the return address matter. String compare hooks use the lowest 12 bits, +// but take the return address as an argument and thus don't require the +// indirection through a trampoline. + +#define REPEAT_8(a) a a a a a a a a + +#define REPEAT_512(a) REPEAT_8(REPEAT_8(REPEAT_8(a))) + +// The first four registers to pass arguments in according to the +// platform-specific x64 calling convention. +#ifdef _WIN64 +#define REG_1 "rcx" +#define REG_2 "rdx" +#define REG_3 "r8" +#define REG_4 "r9" +#else +#define REG_1 "rdi" +#define REG_2 "rsi" +#define REG_3 "rdx" +#define REG_4 "rcx" +#endif + +// Call the function at address `func` with arguments `arg1` and `arg2` while +// ensuring that the return address is `fake_pc` up to a globally constant +// offset. +__attribute__((noinline)) void trampoline(uint64_t arg1, uint64_t arg2, + void *func, uint16_t fake_pc) { + // arg1 and arg2 have to be forwarded according to the x64 calling convention. + // We also fix func and fake_pc to their registers so that we can safely use + // rax below. + [[maybe_unused]] register uint64_t arg1_loc asm(REG_1) = arg1; + [[maybe_unused]] register uint64_t arg2_loc asm(REG_2) = arg2; + [[maybe_unused]] register void *func_loc asm(REG_3) = func; + [[maybe_unused]] register uint64_t fake_pc_loc asm(REG_4) = fake_pc; + asm volatile goto( + // Load RIP-relative address of the end of this function. + "lea %l[end_of_function](%%rip), %%rax \n\t" + "push %%rax \n\t" + // Load RIP-relative address of the ret sled into rax. + "lea ret_sled(%%rip), %%rax \n\t" + // Add the offset of the fake_pc-th ret. + "add %[fake_pc], %%rax \n\t" + // Push the fake return address pointing to that ret. The hook will return + // to it and then immediately return to the end of this function. + "push %%rax \n\t" + // Call func with the fake return address on the stack. + // Function arguments arg1 and arg2 are passed unchanged in the registers + // RDI and RSI as governed by the x64 calling convention. + "jmp *%[func] \n\t" + // Append a sled of 2^9=512 ret instructions. + "ret_sled: \n\t" REPEAT_512("ret \n\t") + : + : "r"(arg1_loc), + "r"(arg2_loc), [func] "r"(func_loc), [fake_pc] "r"(fake_pc_loc) + : "memory" + : end_of_function); + +end_of_function: + return; +} + +namespace { +uintptr_t trampoline_offset = 0; +} + +void set_trampoline_offset() { + // Stores the additive inverse of the current return address modulo 0x200u in + // trampoline_offset. + trampoline_offset = + 0x200u - + (reinterpret_cast<uintptr_t>(__builtin_return_address(0)) & 0x1FFu); +} + +// Computes the additive shift that needs to be applied to the caller PC by +// caller_pc_to_fake_pc to make caller PC and resulting fake return address +// in their lowest 9 bite. This offset is constant for each binary, but may vary +// based on code generation specifics. By calibrating the trampoline, the fuzzer +// behavior is fully determined by the seed. +void CalibrateTrampoline() { + trampoline(0, 0, reinterpret_cast<void *>(&set_trampoline_offset), 0); +} + +// Masks any address down to its lower 9 bits, adjusting for the trampoline +// shift. +__attribute__((always_inline)) inline uint16_t caller_pc_to_fake_pc( + const void *caller_pc) { + return (reinterpret_cast<uintptr_t>(caller_pc) + trampoline_offset) & 0x1FFu; +} + +// The original hooks exposed by libFuzzer. All of these get the caller's +// address via __builtin_return_address(0). +extern "C" { +void __sanitizer_cov_trace_cmp4(uint32_t arg1, uint32_t arg2); +void __sanitizer_cov_trace_cmp8(uint64_t arg1, uint64_t arg2); +void __sanitizer_cov_trace_switch(uint64_t val, uint64_t *cases); +void __sanitizer_cov_trace_div4(uint32_t val); +void __sanitizer_cov_trace_div8(uint64_t val); +void __sanitizer_cov_trace_gep(uintptr_t idx); +void __sanitizer_cov_trace_pc_indir(uintptr_t callee); +} +void __sanitizer_cov_trace_cmp4_with_pc(void *caller_pc, uint32_t arg1, + uint32_t arg2) { + void *trace_cmp4 = reinterpret_cast<void *>(&__sanitizer_cov_trace_cmp4); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(arg1), static_cast<uint64_t>(arg2), + trace_cmp4, fake_pc); +} + +void __sanitizer_cov_trace_cmp8_with_pc(void *caller_pc, uint64_t arg1, + uint64_t arg2) { + void *trace_cmp8 = reinterpret_cast<void *>(&__sanitizer_cov_trace_cmp8); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(arg1), static_cast<uint64_t>(arg2), + trace_cmp8, fake_pc); +} + +void __sanitizer_cov_trace_switch_with_pc(void *caller_pc, uint64_t val, + uint64_t *cases) { + void *trace_switch = reinterpret_cast<void *>(&__sanitizer_cov_trace_switch); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(val), reinterpret_cast<uint64_t>(cases), + trace_switch, fake_pc); +} + +void __sanitizer_cov_trace_div4_with_pc(void *caller_pc, uint32_t val) { + void *trace_div4 = reinterpret_cast<void *>(&__sanitizer_cov_trace_div4); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(val), 0, trace_div4, fake_pc); +} + +void __sanitizer_cov_trace_div8_with_pc(void *caller_pc, uint64_t val) { + void *trace_div8 = reinterpret_cast<void *>(&__sanitizer_cov_trace_div8); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(val), 0, trace_div8, fake_pc); +} + +void __sanitizer_cov_trace_gep_with_pc(void *caller_pc, uintptr_t idx) { + void *trace_gep = reinterpret_cast<void *>(&__sanitizer_cov_trace_gep); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(idx), 0, trace_gep, fake_pc); +} + +void __sanitizer_cov_trace_pc_indir_with_pc(void *caller_pc, uintptr_t callee) { + void *trace_pc_indir = + reinterpret_cast<void *>(&__sanitizer_cov_trace_pc_indir); + auto fake_pc = caller_pc_to_fake_pc(caller_pc); + trampoline(static_cast<uint64_t>(callee), 0, trace_pc_indir, fake_pc); +} |