gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/tools/checkescape/checkescape_arm64.go (about)

     1  // Copyright 2022 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package checkescape
    16  
    17  import (
    18  	"fmt"
    19  	"strconv"
    20  	"strings"
    21  )
    22  
    23  // fixOffset accounts for the output of arm64 `go tool objdump`. Objdump gives
    24  // the instruction offset rather than the byte offset. The offset confuses
    25  // checkescape, as it looks like the branch is to random memory.
    26  //
    27  // When appropriate, we re-parse the instruction ourselves and return the
    28  // correct offset.
    29  func fixOffset(fields []string, target string) (string, error) {
    30  	// We're looking for a line that looks something like:
    31  	//   iptables.go:320   0x211214        97f9b198          CALL -413288(PC)
    32  	// In this case, target is passed as -413288(PC). The byte offset of this
    33  	// instruction should be -1653152.
    34  
    35  	// Make sure we're dealing with a PC offset.
    36  	if !strings.HasSuffix(target, "(PC)") {
    37  		return target, nil // Not a relative branch.
    38  	}
    39  
    40  	// Examine the opcode to ensure it's a BL instruction. See the ARM
    41  	// documentation here:
    42  	// https://developer.arm.com/documentation/ddi0596/2020-12/Base-Instructions/BL--Branch-with-Link-?lang=en
    43  	const (
    44  		opcodeBits = 0xfc000000
    45  		blOpcode   = 0x94000000
    46  	)
    47  	instr64, err := strconv.ParseUint(fields[2], 16, 32)
    48  	if err != nil {
    49  		return "", err
    50  	}
    51  	instr := uint32(instr64)
    52  	if instr&opcodeBits != blOpcode {
    53  		return target, nil // Not a BL.
    54  	}
    55  	// Per documentation, the offset is formed via:
    56  	//   - Take the lower 26 bits
    57  	//   - Append 2 zero bits (this is what objdump omits)
    58  	//   - Sign extend out to 64 bits
    59  	offset := int64(int32(instr<<6) >> 4)
    60  
    61  	// Parse the PC, removing the leading "0x".
    62  	pc, err := strconv.ParseUint(fields[1][len("0x"):], 16, 64)
    63  	if err != nil {
    64  		return "", err
    65  	}
    66  	// PC is always the next instruction.
    67  	pc += 8
    68  	return fmt.Sprintf("0x%x", pc+uint64(offset)), nil
    69  }