使用 dd 转储映射缓冲区

Question

进入/proc/PID/maps我可以看到一些缓冲区映射到内核模块的内存：

44a00000-44b00000 rwxs 00000000 00:01 XXXX /dev/my_module

我知道它是逻辑地址，我想用dd?

dd 需要获取物理内存地址，我如何计算这个缓冲区的物理地址来转储它？

Answer 1

有多种方法可以获取与 Linux 上正在运行的进程相关的内存信息。

首先，我们确定要从中获取信息的正在运行的实例的进程 ID 。在此测试中，我在 google.com 上运行 ping。

unknown@unknown-pi4:~$  sudo ps aux | grep ping
unkno+    1402  0.0  0.1 311860  6376 ?        Ssl  15:31   0:01 /usr/libexec/gsd-housekeeping
unknon+    3716  0.0  0.0   9952  2108 pts/0    T    18:11   0:00 ping www.google.com
unknow+    4152  0.1  0.0   9952  2108 pts/0    S+   20:07   0:00 ping www.google.com
unknow+    4176  0.0  0.0   8604   824 pts/1    S+   20:12   0:00 grep --color=auto ping

其次，使用 /proc/$pid/maps 查找有关进程的更多信息。/proc/$pid/maps 提供虚拟地址映射列表以及附加信息，例如映射文件的相应文件。

# https://man7.org/linux/man-pages/man5/proc.5.html

sudo head -1 /proc/3716/maps

aaaab61cf000-aaaab61df000 r-xp 00000000 b3:02 3748                       /usr/bin/ping

第三，使用/proc/$pid/pagemap查看内存。/proc/$pid/pagemap 提供有关每个映射页面的附加信息，包括物理地址，但前提是它存在。

# https://man7.org/linux/man-pages/man5/proc.5.html
# https://linux.die.net/man/1/xxd

sudo cat /proc/3716/pagemap | xxd | less

00000220: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000230: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000240: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000250: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000260: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000270: 0000 0000 0000 0000 0000 0000 0000 0000  ................

最后我们要使用 dd

• dd - 转换并复制文件
• https://man7.org/linux/man-pages/man1/dd.1.html

命令分解：

• sudo = 请求使用 dd 的权限
• if=FILE 从 FILE 而不是 stdin 读取
• Skip=N 在输入开始时跳过 N 个 ibs 大小的块
• bs=BYTES 一次最多读写 BYTES 字节（默认值：512）；覆盖 ibs 和 obs
• count=N 仅复制 N 个输入块
• od - 以八进制和其他格式转储文件
• -t, --format=TYPE 选择输出格式或格式
• x[SIZE] 十六进制，每个整数的 SIZE 字节
• 命名字符，忽略高位

unknown@unknown-pi4:/tmp$ sudo dd if=/proc/3716/mem skip=$((0xaaaab61cf000))  bs=1 count=128 | od -t x1a
dd: /proc/3716/mem: cannot skip to specified offset
0000000  7f  45  4c  46  02  01  01  00  00  00  00  00  00  00  00  00
        del   E   L   F stx soh soh nul nul nul nul nul nul nul nul nul
0000020  03  00  b7  00  01  00  00  00  e0  32  00  00  00  00  00  00
        etx nul   7 nul soh nul nul nul   `   2 nul nul nul nul nul nul
0000040  40  00  00  00  00  00  00  00  18  04  01  00  00  00  00  00
          @ nul nul nul nul nul nul nul can eot soh nul nul nul nul nul
0000060  00  00  00  00  40  00  38  00  09  00  40  00  1a  00  19  00
        nul nul nul nul   @ nul   8 nul  ht nul   @ nul sub nul  em nul
0000100  06  00  00  00  04  00  00  00  40  00  00  00  00  00  00  00
        ack nul nul nul eot nul nul nul   @ nul nul nul nul nul nul nul
0000120  40  00  00  00  00  00  00  00  40  00  00  00  00  00  00  00
          @ nul nul nul nul nul nul nul   @ nul nul nul nul nul nul nul
0000140  f8  01  00  00  00  00  00  00  f8  01  00  00  00  00  00  00
          x soh nul nul nul nul nul nul   x soh nul nul nul nul nul nul
0000160  08  00  00  00  00  00  00  00  03  00  00  00  04  00  00  00
128+0 records in
128+0 records out
         bs nul nul nul nul nul nul nul etx nul nul nul eot nul nul nul
128 bytes copied, 0.0019137 s, 66.9 kB/s
0000200

这是另一个 dd 命令，可让您查看 PID 内存中的字符串。

unknown@unknown-pi4:~$ sudo grep heap /proc/3716/maps
aaaad44ed000-aaaad450e000 rw-p 00000000 00:00 0                          [heap]

# note where I place the mapping addresses in this command.
unknown@unknown-pi4:~$ sudo dd if=/proc/3716/mem bs=1 skip=$((0xaaaad44ed000)) count=$((0xaaaad450e000-0xaaaad44ed000)) status=none | strings | less

GDB - GNU 项目调试器

还有其他方法可以查看正在运行的进程的内存。一种方法是使用 gdb 等调试器。调试器知道进程使用的结构，并且可以跟踪指针和其他项。

您可以通过以下方式将进程转储到文件中：

# http://www.yolinux.com/TUTORIALS/GDB-Commands.html

unknown@unknown-pi4:~$ sudo gdb --pid=3716
(gdb) gcore
(gdb) deatch 
# to exit control z

该文件将存储为 core.3716，可以使用 cat 读取。

您还可以使用 pmap 获取有关进程的信息。

• pmap - 报告进程的内存映射
• https://man7.org/linux/man-pages/man1/pmap.1.html

unknown@unknown-pi4:/tmp$ pmap -XX 1402 | grep ping
1402:   /usr/libexec/gsd-housekeeping
     Address Perm   Offset Device  Inode   Size KernelPageSize MMUPageSize  Rss  Pss Shared_Clean Shared_Dirty Private_Clean Private_Dirty Referenced Anonymous LazyFree AnonHugePages ShmemPmdMapped FilePmdMapped Shared_Hugetlb Private_Hugetlb Swap SwapPss Locked THPeligible              VmFlags Mapping
aaaabe75b000 r-xp 00000000  b3:02  31059     40              4           4   20   20            0            0            20             0         20         0        0             0              0             0              0               0    0       0      0           0    rd ex mr mw me dw gsd-housekeeping
aaaabe775000 r--p 0000a000  b3:02  31059      4              4           4    4    4            0            0             0             4          4         4        0             0              0             0              0               0    0       0      0           0    rd mr mw me dw ac gsd-housekeeping
aaaabe776000 rw-p 0000b000  b3:02  31059      4              4           4    4    4            0            0             0             4          4         4        0             0              0             0              0               0    0       0      0           0 rd wr mr mw me dw ac gsd-housekeeping

在我的 Ubuntu 系统上，我必须暂时禁用运行一些需要 ptrace 的命令的限制。

文件名：

/etc/sysctl.d/10-ptrace.conf

改变这一行：

kernel.yama.ptrace_scope = 1

对此：

kernel.yama.ptrace_scope = 0

您还可以使用脚本转储内存。

touch dump_process_memory

chmod +x dump_process_memory.sh

#!/bin/bash

grep rw-p /proc/$1/maps \
| sed -n 's/^\([0-9a-f]*\)-\([0-9a-f]*\) .*$/\1 \2/p' \
| while read start stop; do \
    gdb --batch --pid $1 -ex \
        "dump memory $1-$start-$stop.dump 0x$start 0x$stop"; \
done

sudo ./dump_process_memory.sh PID

还有各种开源工具可用于内存取证。

• AVML（获取 Linux 的易失性内存）：https ://github.com/microsoft/avml

• LiME ~ Linux 内存提取器：https://github.com/504ensicsLabs/LiME

• 波动性： https: //github.com/volatilityfoundation/volatility

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My system information
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Platform:     Ubuntu
OS Version:   20.10 (Groovy Gorilla)
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