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| -rw-r--r-- | src/runtime/libfuzzer_amd64.s | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/src/runtime/libfuzzer_amd64.s b/src/runtime/libfuzzer_amd64.s new file mode 100644 index 0000000..e30b768 --- /dev/null +++ b/src/runtime/libfuzzer_amd64.s @@ -0,0 +1,158 @@ +// Copyright 2019 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +//go:build libfuzzer + +#include "go_asm.h" +#include "go_tls.h" +#include "textflag.h" + +// Based on race_amd64.s; see commentary there. + +#ifdef GOOS_windows +#define RARG0 CX +#define RARG1 DX +#define RARG2 R8 +#define RARG3 R9 +#else +#define RARG0 DI +#define RARG1 SI +#define RARG2 DX +#define RARG3 CX +#endif + +// void runtime·libfuzzerCall4(fn, hookId int, s1, s2 unsafe.Pointer, result uintptr) +// Calls C function fn from libFuzzer and passes 4 arguments to it. +TEXT runtime·libfuzzerCall4(SB), NOSPLIT, $0-40 + MOVQ fn+0(FP), AX + MOVQ hookId+8(FP), RARG0 + MOVQ s1+16(FP), RARG1 + MOVQ s2+24(FP), RARG2 + MOVQ result+32(FP), RARG3 + + get_tls(R12) + MOVQ g(R12), R14 + MOVQ g_m(R14), R13 + + // Switch to g0 stack. + MOVQ SP, R12 // callee-saved, preserved across the CALL + MOVQ m_g0(R13), R10 + CMPQ R10, R14 + JE call // already on g0 + MOVQ (g_sched+gobuf_sp)(R10), SP +call: + ANDQ $~15, SP // alignment for gcc ABI + CALL AX + MOVQ R12, SP + RET + +// void runtime·libfuzzerCallTraceIntCmp(fn, arg0, arg1, fakePC uintptr) +// Calls C function fn from libFuzzer and passes 2 arguments to it after +// manipulating the return address so that libfuzzer's integer compare hooks +// work +// libFuzzer's compare hooks obtain the caller's address from the compiler +// builtin __builtin_return_address. Since we 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. +// TODO: Remove the inline assembly trampoline once a PC argument has been added to libfuzzer's int compare hooks. +TEXT runtime·libfuzzerCallTraceIntCmp(SB), NOSPLIT, $0-32 + MOVQ fn+0(FP), AX + MOVQ arg0+8(FP), RARG0 + MOVQ arg1+16(FP), RARG1 + MOVQ fakePC+24(FP), R8 + + get_tls(R12) + MOVQ g(R12), R14 + MOVQ g_m(R14), R13 + + // Switch to g0 stack. + MOVQ SP, R12 // callee-saved, preserved across the CALL + MOVQ m_g0(R13), R10 + CMPQ R10, R14 + JE call // already on g0 + MOVQ (g_sched+gobuf_sp)(R10), SP +call: + ANDQ $~15, SP // alignment for gcc ABI + SUBQ $8, SP + // Load the address of the end of the function and push it into the stack. + // This address will be jumped to after executing the return instruction + // from the return sled. There we reset the stack pointer and return. + MOVQ $end_of_function<>(SB), BX + PUSHQ BX + // Load the starting address of the return sled into BX. + MOVQ $ret_sled<>(SB), BX + // Load the address of the i'th return instruction from the return sled. + // The index is given in the fakePC argument. + ADDQ R8, BX + PUSHQ BX + // Call the original function with the fakePC return address on the stack. + // Function arguments arg0 and arg1 are passed in the registers specified + // by the x64 calling convention. + JMP AX +// This code will not be executed and is only there to satisfy assembler +// check of a balanced stack. +not_reachable: + POPQ BX + POPQ BX + RET + +TEXT end_of_function<>(SB), NOSPLIT, $0-0 + MOVQ R12, SP + RET + +#define REPEAT_8(a) a \ + a \ + a \ + a \ + a \ + a \ + a \ + a + +#define REPEAT_512(a) REPEAT_8(REPEAT_8(REPEAT_8(a))) + +TEXT ret_sled<>(SB), NOSPLIT, $0-0 + REPEAT_512(RET) + +// void runtime·libfuzzerCallWithTwoByteBuffers(fn, start, end *byte) +// Calls C function fn from libFuzzer and passes 2 arguments of type *byte to it. +TEXT runtime·libfuzzerCallWithTwoByteBuffers(SB), NOSPLIT, $0-24 + MOVQ fn+0(FP), AX + MOVQ start+8(FP), RARG0 + MOVQ end+16(FP), RARG1 + + get_tls(R12) + MOVQ g(R12), R14 + MOVQ g_m(R14), R13 + + // Switch to g0 stack. + MOVQ SP, R12 // callee-saved, preserved across the CALL + MOVQ m_g0(R13), R10 + CMPQ R10, R14 + JE call // already on g0 + MOVQ (g_sched+gobuf_sp)(R10), SP +call: + ANDQ $~15, SP // alignment for gcc ABI + CALL AX + MOVQ R12, SP + RET |