src/runtime/libfuzzer.go

// 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

package runtime

import "unsafe"

func libfuzzerCallWithTwoByteBuffers(fn, start, end *byte)
func libfuzzerCallTraceIntCmp(fn *byte, arg0, arg1, fakePC uintptr)
func libfuzzerCall4(fn *byte, fakePC uintptr, s1, s2 unsafe.Pointer, result uintptr)

// Keep in sync with the definition of ret_sled in src/runtime/libfuzzer_amd64.s
const retSledSize = 512

// In libFuzzer mode, the compiler inserts calls to libfuzzerTraceCmpN and libfuzzerTraceConstCmpN
// (where N can be 1, 2, 4, or 8) for encountered integer comparisons in the code to be instrumented.
// This may result in these functions having callers that are nosplit. That is why they must be nosplit.
//
//go:nosplit
func libfuzzerTraceCmp1(arg0, arg1 uint8, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_cmp1, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceCmp2(arg0, arg1 uint16, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_cmp2, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceCmp4(arg0, arg1 uint32, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_cmp4, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceCmp8(arg0, arg1 uint64, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_cmp8, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceConstCmp1(arg0, arg1 uint8, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_const_cmp1, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceConstCmp2(arg0, arg1 uint16, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_const_cmp2, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceConstCmp4(arg0, arg1 uint32, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_const_cmp4, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

//go:nosplit
func libfuzzerTraceConstCmp8(arg0, arg1 uint64, fakePC uint) {
	fakePC = fakePC % retSledSize
	libfuzzerCallTraceIntCmp(&__sanitizer_cov_trace_const_cmp8, uintptr(arg0), uintptr(arg1), uintptr(fakePC))
}

var pcTables []byte

func init() {
	libfuzzerCallWithTwoByteBuffers(&__sanitizer_cov_8bit_counters_init, &__start___sancov_cntrs, &__stop___sancov_cntrs)
	start := unsafe.Pointer(&__start___sancov_cntrs)
	end := unsafe.Pointer(&__stop___sancov_cntrs)

	// PC tables are arrays of ptr-sized integers representing pairs [PC,PCFlags] for every instrumented block.
	// The number of PCs and PCFlags is the same as the number of 8-bit counters. Each PC table entry has
	// the size of two ptr-sized integers. We allocate one more byte than what we actually need so that we can
	// get a pointer representing the end of the PC table array.
	size := (uintptr(end)-uintptr(start))*unsafe.Sizeof(uintptr(0))*2 + 1
	pcTables = make([]byte, size)
	libfuzzerCallWithTwoByteBuffers(&__sanitizer_cov_pcs_init, &pcTables[0], &pcTables[size-1])
}

// We call libFuzzer's __sanitizer_weak_hook_strcmp function which takes the
// following four arguments:
//
//  1. caller_pc: location of string comparison call site
//  2. s1: first string used in the comparison
//  3. s2: second string used in the comparison
//  4. result: an integer representing the comparison result. 0 indicates
//     equality (comparison will ignored by libfuzzer), non-zero indicates a
//     difference (comparison will be taken into consideration).
//
//go:nosplit
func libfuzzerHookStrCmp(s1, s2 string, fakePC int) {
	if s1 != s2 {
		libfuzzerCall4(&__sanitizer_weak_hook_strcmp, uintptr(fakePC), cstring(s1), cstring(s2), uintptr(1))
	}
	// if s1 == s2 we could call the hook with a last argument of 0 but this is unnecessary since this case will be then
	// ignored by libfuzzer
}

// This function has now the same implementation as libfuzzerHookStrCmp because we lack better checks
// for case-insensitive string equality in the runtime package.
//
//go:nosplit
func libfuzzerHookEqualFold(s1, s2 string, fakePC int) {
	if s1 != s2 {
		libfuzzerCall4(&__sanitizer_weak_hook_strcmp, uintptr(fakePC), cstring(s1), cstring(s2), uintptr(1))
	}
}

//go:linkname __sanitizer_cov_trace_cmp1 __sanitizer_cov_trace_cmp1
//go:cgo_import_static __sanitizer_cov_trace_cmp1
var __sanitizer_cov_trace_cmp1 byte

//go:linkname __sanitizer_cov_trace_cmp2 __sanitizer_cov_trace_cmp2
//go:cgo_import_static __sanitizer_cov_trace_cmp2
var __sanitizer_cov_trace_cmp2 byte

//go:linkname __sanitizer_cov_trace_cmp4 __sanitizer_cov_trace_cmp4
//go:cgo_import_static __sanitizer_cov_trace_cmp4
var __sanitizer_cov_trace_cmp4 byte

//go:linkname __sanitizer_cov_trace_cmp8 __sanitizer_cov_trace_cmp8
//go:cgo_import_static __sanitizer_cov_trace_cmp8
var __sanitizer_cov_trace_cmp8 byte

//go:linkname __sanitizer_cov_trace_const_cmp1 __sanitizer_cov_trace_const_cmp1
//go:cgo_import_static __sanitizer_cov_trace_const_cmp1
var __sanitizer_cov_trace_const_cmp1 byte

//go:linkname __sanitizer_cov_trace_const_cmp2 __sanitizer_cov_trace_const_cmp2
//go:cgo_import_static __sanitizer_cov_trace_const_cmp2
var __sanitizer_cov_trace_const_cmp2 byte

//go:linkname __sanitizer_cov_trace_const_cmp4 __sanitizer_cov_trace_const_cmp4
//go:cgo_import_static __sanitizer_cov_trace_const_cmp4
var __sanitizer_cov_trace_const_cmp4 byte

//go:linkname __sanitizer_cov_trace_const_cmp8 __sanitizer_cov_trace_const_cmp8
//go:cgo_import_static __sanitizer_cov_trace_const_cmp8
var __sanitizer_cov_trace_const_cmp8 byte

//go:linkname __sanitizer_cov_8bit_counters_init __sanitizer_cov_8bit_counters_init
//go:cgo_import_static __sanitizer_cov_8bit_counters_init
var __sanitizer_cov_8bit_counters_init byte

// start, stop markers of counters, set by the linker
var __start___sancov_cntrs, __stop___sancov_cntrs byte

//go:linkname __sanitizer_cov_pcs_init __sanitizer_cov_pcs_init
//go:cgo_import_static __sanitizer_cov_pcs_init
var __sanitizer_cov_pcs_init byte

//go:linkname __sanitizer_weak_hook_strcmp __sanitizer_weak_hook_strcmp
//go:cgo_import_static __sanitizer_weak_hook_strcmp
var __sanitizer_weak_hook_strcmp byte