Re: Using a custom dyld on 10.11

Subject: Re: Using a custom dyld on 10.11
From: Daniel Peebles <email@hidden>
Date: Thu, 07 Jan 2016 23:30:04 -0500

Okay, a friend of mine pointed out that this is very explicitly disallowed in the new 10.11 xnu public source release. I'm quite disappointed that a perfectly valid mach-o file is now being rejected, seemingly arbitrarily, by my OS.

#if !(DEVELOPMENT || DEBUG)
	if (0 != strcmp(name, DEFAULT_DYLD_PATH)) {
		return (LOAD_BADMACHO);
	}
#endif

(from http://www.opensource.apple.com/source/xnu/xnu-3247.1.106/bsd/kern/mach_loader.c)

Does anyone on here have any explanation for this change? Was it intended as some sort of security measure? I can't even turn it off by disabling SIP :/

rdar://24102922

Thanks,

Dan

On Wed, Jan 6, 2016 at 3:20 PM, Daniel Peebles <email@hidden> wrote:

Yeah. That intuitively feels like it should be (not sure if it actually is) permitted assuming that I'm not trying to change any system executables, right? My self-built executable has a custom LC_LOAD_DYLINKER pointing to my self-built dyld (or attempt at one, at least :P you folks don't exactly make it easy!)

Even a much simpler test fails: if I copy /usr/lib/dyld to my home folder and build a new executable pointing at the copy of dyld, it refuses to start. I don't have the error messages handy right now, but can dig them up if that would help.

Thanks,
Dan
On Wed, Jan 6, 2016 at 3:16 PM, Greg Parker <email@hidden> wrote:
Dan, are you trying to run an executable with a custom LC_LOAD_DYLINKER command?

On Jan 6, 2016, at 11:58 AM, Daniel Peebles <email@hidden> wrote:

I understand that, I think. TBC, I'm definitely not trying to overwrite /usr/lib/dyld, which I would expect to be blocked by SIP. Instead, I'm trying to build a new mach-o file that points at a dyld that I'm building myself. Would you expect SIP to block that? I'm seeing some weird behavior that I believe is due to SIP, but I might be misattributing the failure.

Thanks,
Dan

On Wed, Jan 6, 2016 at 2:49 PM, Shantonu Sen <email@hidden> wrote:
Any experimentation with system-level components requires disabling SIP, as well as potentially rebuilding other open source components of OS X.

Shantonu

> On Jan 6, 2016, at 9:15 AM, Daniel Peebles <email@hidden> wrote:
>
> Hi all,
>
> I've been experimenting with building my own dyld but I'm getting the sense that SIP on 10.11 prevents us from running Mach-O binaries that with interpreters set to anything but /usr/lib/dyld. Is that correct? If so, is there a way to turn off that control without turning off system-wide SIP?
>
> Thanks,
> Dan
>

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References:

>Using a custom dyld on 10.11 (From: Daniel Peebles <email@hidden>)

>Re: Using a custom dyld on 10.11 (From: Daniel Peebles <email@hidden>)

>Re: Using a custom dyld on 10.11 (From: Greg Parker <email@hidden>)

>Re: Using a custom dyld on 10.11 (From: Daniel Peebles <email@hidden>)

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