Question

首先，我尝试对它进行一些逆向工程：

printf '
#include <stdio.h>
int main() {
    puts("hello world");
}
' > main.c
gcc -std=c99 -pie -fpie -ggdb3 -o pie main.c
echo 2 | sudo tee /proc/sys/kernel/randomize_va_space
readelf -s ./pie | grep -E 'main$'
gdb -batch -nh \
  -ex 'set disable-randomization off' \
  -ex 'start' -ex 'info line' \
  -ex 'start' -ex 'info line' \
  -ex 'set disable-randomization on' \
  -ex 'start' -ex 'info line' \
  -ex 'start' -ex 'info line' \
  ./pie \
;

输出：

64: 000000000000063a    23 FUNC    GLOBAL DEFAULT   14 main
Temporary breakpoint 1, main () at main.c:4
4           puts("hello world");
Line 4 of "main.c" starts at address 0x5575f5fd263e <main+4> and ends at 0x5575f5fd264f <main+21>.
Temporary breakpoint 2 at 0x5575f5fd263e: file main.c, line 4.

Temporary breakpoint 2, main () at main.c:4
4           puts("hello world");
Line 4 of "main.c" starts at address 0x55e3fbc9363e <main+4> and ends at 0x55e3fbc9364f <main+21>.
Temporary breakpoint 3 at 0x55e3fbc9363e: file main.c, line 4.

Temporary breakpoint 3, main () at main.c:4
4           puts("hello world");
Line 4 of "main.c" starts at address 0x55555555463e <main+4> and ends at 0x55555555464f <main+21>.
Temporary breakpoint 4 at 0x55555555463e: file main.c, line 4.

Temporary breakpoint 4, main () at main.c:4
4           puts("hello world");
Line 4 of "main.c" starts at address 0x55555555463e <main+4> and ends at 0x55555555464f <main+21>.

表示它是0x555555554000 +随机偏移量+ 63e。

但是后来我尝试为555555554复制Linux内核和glibc源代码，但没有成功。

哪个代码中的哪一部分计算该地址？

我在回答What is the -fPIE option for position-independent executables in gcc and ld?

时遇到了这个问题

Answer 1

某些 Internet搜索为0x555555554000提示：ThreadSanitizer https://github.com/google/sanitizers/wiki/ThreadSanitizerCppManual

存在问题

问：运行程序时，它说：致命：ThreadSanitizer无法映射影子内存（某些内容映射为0x555555554000 <0x7cf000000000）。该怎么办？您需要启用ASLR：
 $ echo 2 >/proc/sys/kernel/randomize_va_space
此问题可能会在以后的内核中修复，请参见https://bugzilla.kernel.org/show_bug.cgi?id=66721 ...
 $ gdb -ex 'set disable-randomization off' --args ./a.out

和https://lwn.net/Articles/730120/“稳定的内核更新”。由hmh（订阅者）于2017年8月7日世界标准时间（星期一）发布https://marc.info/?t=150213704600001&r=1&w=2 （https://patchwork.kernel.org/patch/9886105/，commit c715b72c1ba4）

将x86_64和arm64 PIE基础从0x555555554000移动到0x000100000000   破坏了AddressSanitizer。这是以下内容的部分还原：


commit eab09532d400（“ binfmt_elf：仅将ELF_ET_DYN_BASE用于PIE”）（https://patchwork.kernel.org/patch/9807325/ https://lkml.org/lkml/2017/6/21/560）

commit 02445990a96e（“ arm64：将ELF_ET_DYN_BASE移至4GB / 4MB”）（https://patchwork.kernel.org/patch/9807319/）

还原后的代码为：

b/arch/arm64/include/asm/elf.h
 /*
  * This is the base location for PIE (ET_DYN with INTERP) loads. On
- * 64-bit, this is raised to 4GB to leave the entire 32-bit address
+ * 64-bit, this is above 4GB to leave the entire 32-bit address   * space open for things that want to use the area for 32-bit pointers.   */
-#define ELF_ET_DYN_BASE      0x100000000UL
+#define ELF_ET_DYN_BASE      (2 * TASK_SIZE_64 / 3)


+++ b/arch/x86/include/asm/elf.h
 /*
  * This is the base location for PIE (ET_DYN with INTERP) loads. On
- * 64-bit, this is raised to 4GB to leave the entire 32-bit address
+ * 64-bit, this is above 4GB to leave the entire 32-bit address
  * space open for things that want to use the area for 32-bit pointers.
  */
 #define ELF_ET_DYN_BASE      (mmap_is_ia32() ? 0x000400000UL : \
-                       0x100000000UL)
+                       (TASK_SIZE / 3 * 2))

因此，0x555555554000与ELF_ET_DYN_BASE macro（在fs/binfmt_elf.c for ET_DYN as not randomized load_bias中引用）相关，对于x86_64和arm64，它类似于TASK_SIZE的2/3。如果没有CONFIG_X86_32，则x86_64的TASK_SIZE为2^47 - one page in arch/x86/include/asm/processor.h

/*
 * User space process size. 47bits minus one guard page.  The guard
 * page is necessary on Intel CPUs: if a SYSCALL instruction is at
 * the highest possible canonical userspace address, then that
 * syscall will enter the kernel with a non-canonical return
 * address, and SYSRET will explode dangerously.  We avoid this
 * particular problem by preventing anything from being mapped
 * at the maximum canonical address.
 */
#define TASK_SIZE_MAX   ((1UL << 47) - PAGE_SIZE)

旧版本：

/*
 * User space process size. 47bits minus one guard page.
 */
#define TASK_SIZE_MAX   ((1UL << 47) - PAGE_SIZE)

较新的版本也支持5level和__VIRTUAL_MASK_SHIFT of 56 bit-v4.17/source/arch/x86/include/asm/processor.h（但don't want to use it before enabled by user + commit b569bab78d8d ".. Not all user space is ready to handle wide addresses")）。

因此，根据公式 2 ^ 47-1page * 3/2 （对于{{3}，则为2 ^ 56）将0x555555554000向下舍入（按load_bias = ELF_PAGESTART(load_bias - vaddr);，vaddr为零）。 }）：

$ echo 'obase=16; (2^47-4096)/3*2'| bc -q
555555554AAA
$ echo 'obase=16; (2^56-4096)/3*2'| bc -q
AAAAAAAAAAA000

大约2/3的历史记录* TASK_SIZE：

使用2 * TASK_SIZE larger systems和commit 9b1bbf6ea9b2 "use ELF_ET_DYN_BASE only for PIE"不会溢出32位：

几乎所有的拱门都将ELF_ET_DYN_BASE定义为TASK_SIZE的2/3。虽然似乎某些体系结构以错误的方式执行此操作。问题是2 * TASK_SIZE可能溢出32位，所以真正的ELF_ET_DYN_BASE 变得错误。通过在除以TASK_SIZE之前解决此溢出问题乘法：(TASK_SIZE / 3 * 2)

与4.x，3.y，2.6.z相同（davej-history git repo在哪里？"[uml-user] [PATCH] x86, UML: fix integer overflow in ELF_ET_DYN_BASE", 2015和"ARM: 8320/1: fix integer overflow in ELF_ET_DYN_BASE", 2015）2.4.z，... archive 1997年9月6日

diff --git a/include/asm-i386/elf.h b/include/asm-i386/elf.h
+/* This is the location that an ET_DYN program is loaded if exec'ed.  Typical
+   use of this is to invoke "./ld.so someprog" to test out a new version of
+   the loader.  We need to make sure that it is out of the way of the program
+   that it will "exec", and that there is sufficient room for the brk.  */
+
+#define ELF_ET_DYN_BASE         (2 * TASK_SIZE / 3)

在Linux中如何确定PIE可执行文件的文本部分的地址？

1 个答案: