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[原创]逆向进入内核时代之APatch源码学习(01.模拟调试环境搭建, 远离拦路虎)
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发表于: 2024-8-28 10:35
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最近在讲解Linux内核kernel patch的实现原理, 其中不乏优秀的开源项目和内核大神, APatch就是其中之一.
APatch借鉴了magisk patch init和selinux的方式在内核层实现了hook(注意b跳转相关hook, 非inlinehook). 思维巧妙有较高的学习意义.
但是在上手探究原理的过程中, 如果使用真机的方式, 简单修改就会卡机, 需要重刷等.
好的环境是好的开始的前提, 因为我们是探究其原理, 简单过一下项目其实现方式与平台无关, 因此可以通过内核模拟的方式, 使用GDB探究其中的每一步实现, 完美规避.
安装Qemu
注意：不同的qemu版本可能起始的物理地址不同，本人电脑使用ubuntu22.04自带版本，6.2.0
要求：最好自己折腾， 也可以使用我准备好的。
b2dK9s2c8@1M7s2y4Q4x3@1q4Q4x3V1k6Q4x3V1k6Y4K9i4c8Z5N6h3u0Q4x3X3g2U0L8$3#2Q4x3V1k6F1P5X3y4$3i4K6u0r3d9$3g2J5L8X3g2D9f1r3q4@1j5$3S2c8c8f1#2g2i4K6u0r3M7X3g2D9k6h3q4K6k6i4y4Q4x3V1k6@1j5h3N6Q4x3V1k6V1k6i4j5I4i4K6u0W2x3q4)9J5k6e0M7`.(手动编译查看github/workflow）
1.1 使用交叉编译器或者直接官方网站下载:
1.2 下载4.15.2内核
1.3 快速编译命令
要求：最好自己折腾，也可以使用已修改版本
1.1 参考链接
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6.2 制作initrd
// makefile
它是针对地址处的入口点进行编译的0x40080000。
这个确切的地址来自 QEMU 虚拟设备的设计：
0x00000000 - 0x3FFFFFFF是内存映射外设的区域。使用此范围内的地址，您可以访问多个外设的寄存器来配置和控制它们，就像我们使用位于 0x09000000UART 的输出寄存器将文本字符串输出到终端一样。
0x40000000 - 0x4007FFFF是为引导加载程序保留的区域。
并且内核（或任何裸机应用程序）正在加载到地址 0x40080000。外围设备的寄存器
初始地址，即您的内核将被加载到的位置取决于引导加载程序的实现，如果您使用现有的硬件或模拟器，那么您很可能会处理现有的引导加载程序，它会将您的内核文件加载到某个预定义的地址。
2. 断点调试验证
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内核启动后, 可以通过gdb单步调试理解其中细节
9.1 因为内核在被执行之前还有bootloader的存在, 还记得前面qemu的bootloader实现么???
内核启动后我第一步想法是第一行运行代码是什么, 在什么位置呢, 对应的参数又是什么? 我的第一步想法是汇编入口加入延时.
入口延时
在汇编入口加入延时调试, 方便查看地址:
qemu bootloader传入的参数
前面只是自己编译内核并跑了起来, Apatch对应的APK功能包含boot.img解包并提取内核, 进行patch. 因为我们已经有了内核文件
所以可以直接命令行patch
Patched后再到qemu环境里面去跑起来看看吧?? 相信你一定会有所收获
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sudo apt updatesudo apt-get install qemu qemu-system qemu-userroot@happy /s/qemu_linux# qemu-system-aarch64 --versionQEMU emulator version 6.2.0 (Debian 1:6.2+dfsg-2ubuntu6.19)Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developerssudo apt updatesudo apt-get install qemu qemu-system qemu-userroot@happy /s/qemu_linux# qemu-system-aarch64 --versionQEMU emulator version 6.2.0 (Debian 1:6.2+dfsg-2ubuntu6.19)Copyright (c) 2003-2021 Fabrice Bellard and the QEMU Project developerssudo apt-get updatesudo apt-get install gcc-10-aarch64-linux-gnusudo mv /usr/bin/aarch64-linux-gnu-gcc-10 /usr/bin/aarch64-linux-gnu-gccsudo apt-get updatesudo apt-get install gcc-10-aarch64-linux-gnusudo mv /usr/bin/aarch64-linux-gnu-gcc-10 /usr/bin/aarch64-linux-gnu-gcc> curl -L -O https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.15.2.tar.gz> curl -L -O https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.15.2.tar.gzsudo apt-get install gitgit clone https://github.com/nzcv/KernelPatchQEMU.gitcd KernelPatchQEMUmake ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfigmake -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-sudo apt-get install gitgit clone https://github.com/nzcv/KernelPatchQEMU.gitcd KernelPatchQEMUmake ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfigmake -j$(nproc) ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-//使用工程内部直接patchpatch lib/Kconfig.debug < ../patch/Kconfig.debug.patch//使用工程内部直接patchpatch lib/Kconfig.debug < ../patch/Kconfig.debug.patchmake menuconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-//default and save exitmake defconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-make -j8 ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-其他配置:CONFIG_DEBUG_KERNEL=ymake menuconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-//default and save exitmake defconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-make -j8 ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-其他配置:CONFIG_DEBUG_KERNEL=ymake menuconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-Settings ---> [*] Build static binary (no shared libs) //静态编译[*] Build with debug information //可选，带调试信息，方便后续调试make menuconfig ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-Settings ---> [*] Build static binary (no shared libs) //静态编译[*] Build with debug information //可选，带调试信息，方便后续调试make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- installfind . | cpio -o --format=newc > ../rootfs.imgmake ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- installfind . | cpio -o --format=newc > ../rootfs.imginit: cd ./initramfs && find . -print0|cpio --null -ov --format=newc|gzip -9>../build/initramfs.cpio.gzrun: qemu-system-aarch64 -kernel Image -initrd build/initramfs.cpio.gz -m 1G -nographic --append "earlyprintk=serail,ttyS0 console=ttyS0"run2: qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image -nographic -append "console=ttyAMA0 root=/dev/vda oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ" -initrd build/initramfs.cpio.gzold: cp ../linux-4.15.2/arch/arm64/boot/Image . qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image -nographic -append "console=ttyAMA0 oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ root=/dev/ram rdinit=/bin/sh" -initrd rootfs.img.gz -S -gdb tcp::9000patch: qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image2 -nographic -append "console=ttyAMA0 oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ root=/dev/ram rdinit=/bin/sh" -initrd rootfs.img.gz -S -gdb tcp::9000init: cd ./initramfs && find . -print0|cpio --null -ov --format=newc|gzip -9>../build/initramfs.cpio.gzrun: qemu-system-aarch64 -kernel Image -initrd build/initramfs.cpio.gz -m 1G -nographic --append "earlyprintk=serail,ttyS0 console=ttyS0"run2: qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image -nographic -append "console=ttyAMA0 root=/dev/vda oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ" -initrd build/initramfs.cpio.gzold: cp ../linux-4.15.2/arch/arm64/boot/Image . qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image -nographic -append "console=ttyAMA0 oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ root=/dev/ram rdinit=/bin/sh" -initrd rootfs.img.gz -S -gdb tcp::9000patch: qemu-system-aarch64 -M virt -cpu cortex-a57 -smp 1 -m 1G -kernel Image2 -nographic -append "console=ttyAMA0 oops=panic panic_on_warn=1 panic=-1 ftrace_dump_on_oops=orig_cpu debug earlyprintk=serial slub_debug=UZ root=/dev/ram rdinit=/bin/sh" -initrd rootfs.img.gz -S -gdb tcp::9000static const ARMInsnFixup bootloader_aarch64[] = { { 0x580000c0 }, /* ldr x0, arg ; Load the lower 32-bits of DTB */ { 0xaa1f03e1 }, /* mov x1, xzr */ { 0xaa1f03e2 }, /* mov x2, xzr */ { 0xaa1f03e3 }, /* mov x3, xzr */ { 0x58000084 }, /* ldr x4, entry ; Load the lower 32-bits of kernel entry */ { 0xd61f0080 }, /* br x4 ; Jump to the kernel entry point */ { 0, FIXUP_ARGPTR_LO }, /* arg: .word @DTB Lower 32-bits */ { 0, FIXUP_ARGPTR_HI}, /* .word @DTB Higher 32-bits */ { 0, FIXUP_ENTRYPOINT_LO }, /* entry: .word @Kernel Entry Lower 32-bits */ { 0, FIXUP_ENTRYPOINT_HI }, /* .word @Kernel Entry Higher 32-bits */ { 0, FIXUP_TERMINATOR }};static const ARMInsnFixup bootloader_aarch64[] = { { 0x580000c0 }, /* ldr x0, arg ; Load the lower 32-bits of DTB */ { 0xaa1f03e1 }, /* mov x1, xzr */ { 0xaa1f03e2 }, /* mov x2, xzr */ { 0xaa1f03e3 }, /* mov x3, xzr */ { 0x58000084 }, /* ldr x4, entry ; Load the lower 32-bits of kernel entry */ { 0xd61f0080 }, /* br x4 ; Jump to the kernel entry point */ { 0, FIXUP_ARGPTR_LO }, /* arg: .word @DTB Lower 32-bits */ { 0, FIXUP_ARGPTR_HI}, /* .word @DTB Higher 32-bits */ { 0, FIXUP_ENTRYPOINT_LO }, /* entry: .word @Kernel Entry Lower 32-bits */ { 0, FIXUP_ENTRYPOINT_HI }, /* .word @Kernel Entry Higher 32-bits */ { 0, FIXUP_TERMINATOR }[培训]内核驱动高级班，冲击BAT一流互联网大厂工作，每周日13:00-18:00直播授课
