iOS安全—阻止tweak注入hook api

在网上看到一种方法可以通过在Other Linker Flags中添加：


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-Wl,-sectcreate,__RESTRICT,__restrict,/dev/null

的方法来阻止dylib注入。

便动手试了一下，编写一个测试Demo不添加任何linker flags，然后使用theos对其进行hook。

启动后使用image list –o –f 来查看加载的动态库：

[145] 0x0025f000 /Library/MobileSubstrate/MobileSubstrate.dylib(0x000000000025f000)
[152] 0x003c0000 /Library/MobileSubstrate/DynamicLibraries/TestLog.dylib(0x00000000003c0000)

发现我们用来hook编写的dylib已经被加载，自然能看到hook成功的log。

2015-11-10 15:21:50.824 myTest[21906:273137] viewDidLoad — 你已经被我Hook了。。。。。。

然后使用linker flags：


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-Wl,-sectcreate,__RESTRICT,__restrict,/dev/null

重新编译生成。

运行后在所有加载的动态库中已找不到hook的dylib，hook失败了，说明这是有效的。

再来看看生成的macho文件多了一个__RESTRICT/__restrict section。

为什么加了这样的一个section就能阻止dylib注入了呢？

在这里找到了答案：http://www.opensource.apple.com/source/dyld/dyld-210.2.3/src/dyld.cpp

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if ( removedCount != 0 ) {
dyld::log("dyld: DYLD_ environment variables being ignored because ");
switch (sRestrictedReason) {
case restrictedNot:
break;
case restrictedBySetGUid:
dyld::log("main executable (%s) is setuid or setgid\n", sExecPath);
break;
case restrictedBySegment:
dyld::log("main executable (%s) has __RESTRICT/__restrict section\n", sExecPath);
break;
case restrictedByEntitlements:
dyld::log("main executable (%s) is code signed with entitlements\n", sExecPath);
break;
}
}

也就是说下面三种情况，可以让环境变量：DYLD_INSERT_LIBRARIES被无视

1.Set restricted status by entitlements

This option is only available to applications on OS X with special entitlements.
2.setuid and setgid

Any application that makes these two calls are going to be marked as restricted by the linker as a security measure.
3.Restricted Segment of Header

The final way to mark a binary as restricted is by telling the linker to add new section to the binary header that is named “__RESTRICT” and has a section named “__restrict” when you compile it.

所以编译生成的含有__RESTRICT/__restrict section的app会忽略DYLD_INSERT_LIBRARIES。

当然解决办法也是有的，把section的名字修改一下即可。

用010 editor打开可执行文件，找到section的名字：