Support for MIPS about injector HOT 9 CLOSED

@enty8080
I added MIPS support.

Well, I recommend that you use this just for fun. It may stop processes. See https://github.com/kubo/injector#caveats.

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@kubo Thanks. Your tool
is great and I hope I won't face such problems, but I do not really understand this caveat. May it stop all the processes including init or just the target process? And any ways to prevent this?

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May it stop all the processes including init or just the target process?

It may stop just the target process.

And any ways to prevent this?

It is possible in theory but it is difficult for me.

The idea is:

1. attach to the target process.
2. get a backtrace of the target process as gdb does.
3. if the backtrace includes memory management functions such as malloc, calloc, strdup, free, step the target process until they disappear from the backtrace.
4. Here is safe to inject a shared library.

If the target process holds a lock used by memory management functions, injector's library loading, which calls malloc internally, tries to hold the same lock in the same thread and stops forever.

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@kubo Thanks for description. Also, I have got a question. So your tool works only on little endian systems or big too? I have this question because in README there are only armel and mipsel, no mipsbe or armbe.

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It will work also on big endian systems though I have not tested it.

I checked that it was compiled by the following compilers on ubuntu 20.04 x86_64. However I could test only three: mipsel n32 (-mabi=n32), mipsel o32 (-mabi=32) and mips64el.

• mips-linux-gnu-gcc (compiler option -mabi=n32)
• mips-linux-gnu-gcc (compiler option -mabi=32)
• mipsel-linux-gnu-gcc (compiler option -mabi=n32)
• mipsel-linux-gnu-gcc (compiler option -mabi=32)
• mips64-linux-gnuabi64-gcc
• mips64el-linux-gnuabi64-gcc
• mipsisa32r6-linux-gnu-gcc (compiler option -mabi=n32)
• mipsisa32r6-linux-gnu-gcc (compiler option -mabi=32)
• mipsisa32r6el-linux-gnu-gcc (compiler option -mabi=n32)
• mipsisa32r6el-linux-gnu-gcc (compiler option -mabi=32)
• mipsisa64r6-linux-gnuabi64-gcc
• mipsisa64r6el-linux-gnuabi64-gcc

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@kubo I am just curious if it will work on embedded Linux. For instance, router that has Linux 2.5 with musl c library and mipsel CPU. I am gonna test this, but I also want to know if you think this will work.

BTW, have you tried to inject dylib to macho process (macOS)?

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I think that it works. Support for musl libc was contributed at #22.

BTW, how about LD_PRELOAD or /etc/ld.so.preload in order to inject libraries?

As for macOS, I won't support it. I don't know how to do it on macOS and I don't have macOS machine suitable for the latest OS. (I have macbook air mid 2013.)

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@kubo I thought LD_PRELOAD can only inject shared library to the app, that you run at the same time. I thought you can't use LD_PRELOAD for injecting .so to the running process.

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@enty8080 You are correct. It isn't in-place replacement of injector. I recommend that you have a rethink about your application design because injector have the caveat I cannot fix.

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