解决mprotect()系统调用失败

Question

我正在编写一些ROP漏洞利用代码,通过系统调用调用mprotect,调用int 0x80后eax设置为0x0表示成功.将执行转移到目标地址仍会产生SIGSEGV.我希望有人能告诉我哪里出错了.

一些细节,目标地址是.data部分,这是我将通过shellcode编写的地方: [20] 0x8146820->0x814c2b8 at 0x000fd820: .data ALLOC LOAD DATA HAS_CONTENTS

我设置eax到125,ebx页面边界0x8146000,ecx以0x1000(4096页大小),并edx以0x7(RWX).

就在系统调用之前,寄存器看起来像这样:

eax            0x7d 125
ecx            0x1000   4096
edx            0x7  7
ebx            0x8146000    135553024
esp            0xbffff2b0   0xbffff2b0
ebp            0x8d0e0f0    0x8d0e0f0
esi            0x804fb85    134544261
edi            0x43434343   1128481603
eip            0x80c0182    0x80c0182 <mprotect+18>
eflags         0x202    [ IF ]
cs             0x73 115
ss             0x7b 123
ds             0x7b 123
es             0x7b 123
fs             0x0  0
gs             0x33 51
(gdb) disas $eip, $eip+20
Dump of assembler code from 0x80c0182 to 0x80c0196:
=> 0x080c0182 <mprotect+18>:    int    $0x80
   0x080c0184 <mprotect+20>:    pop    %ebx
   0x080c0185 <mprotect+21>:    cmp    $0xfffff001,%eax
   0x080c018a <mprotect+26>:    jae    0x80c7d80 <__syscall_error>
   0x080c0190 <mprotect+32>:    ret    

在系统调用之后,寄存器是:

(gdb) si
0x080c0184 in mprotect ()
(gdb) i r
eax            0x0  0
ecx            0x1000   4096
edx            0x7  7
ebx            0x8146000    135553024
esp            0xbffff2b0   0xbffff2b0
ebp            0x8d0e0f0    0x8d0e0f0
esi            0x804fb85    134544261
edi            0x43434343   1128481603
eip            0x80c0184    0x80c0184 <mprotect+20>
eflags         0x202    [ IF ]
cs             0x73 115
ss             0x7b 123
ds             0x7b 123
es             0x7b 123
fs             0x0  0
gs             0x33 51

但是,内存位置不会显示权限更改,并且尝试执行指令会终止应用程序:

(gdb) x/4x 0x8146820
0x8146820:      0x00000000      0x00000000      0x08146154      0x0000ea60
(gdb) c
Continuing.

Program received signal SIGSEGV, Segmentation fault.
0x08146820 in data_start ()

欢迎任何有关如何/调试或我做错的建议.

编辑 我在没有附加调试器的情况下在strace下运行它,似乎mprotect调用成功,但执行失败:

stat64("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2197, ...}) = 0
mprotect(0x8146000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0} ---
+++ killed by SIGSEGV (core dumped) +++

从核心确认崩溃地址:

Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x08146820 in data_start ()

Answer 1

你的mprotect调用工作正常.该程序崩溃,因为0x8146820hold 0x0000,disassembles add [eax], al,并eax保持为零.但地址0未映射.(这就是segfault的原因si_addr=0)