From: Carlos O'Donell <carlos@redhat.com>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
Generic System V Application Binary Interface
<generic-abi@googlegroups.com>,
gnu-gabi@sourceware.org
Subject: Re: RFC: Audit external function called indirectly via GOT
Date: Mon, 01 Jan 2018 00:00:00 -0000 [thread overview]
Message-ID: <76f5551d-e8dc-4915-e3d8-54a2305a5718@redhat.com> (raw)
In-Reply-To: <87po3wo589.fsf@mid.deneb.enyo.de>
On 03/22/2018 03:59 AM, Florian Weimer wrote:
> * Carlos O'Donell:
>
>> On 03/21/2018 03:04 PM, Florian Weimer wrote:
>>> * H. J. Lu:
>>>
>>>>> Could we ship a template for the PLT entries in ld.so instead? And if
>>>>> needed, map it from the file together with an address array, like this?
>>>>
>>>> This won't work since linker needs to know exactly PLT layout to generate
>>>> JUMP_SLOT relocations for LD_AUDIT.
>>>
>>> Why would we need JUMP_SLOT relocations? Couldn't we install suitable
>>> interceptors for GLOB_DAT relocations instead, as long as they resolve
>>> to external function symbols?
>>
>> I think your suggestion might work, but why alter the existing
>> behaviour which users expect and is documented in countless linker
>> text books?
>
> If you have references, please add them to the glibc implementation or
> the wiki. It would certainly help those who are trying to work on the
> code.
Well, Levin's "Linker's and Loaders"
https://www.iecc.com/linker/linker10.html, is the immediate reference
that I have on my shelf, and that developers working on glibc/binutils
should read.
Likewise "Computer Systems: A Programmer's Perspective" by Bryant and
O'Halloran. Chapter 7 "Linking." which covers explicitly how the present
GOT and PLT work.
I have added these under developer resources on the wiki front page.
> My understanding is that the whole thing is quite underdocumented.
> For LD_AUDIT in particular, we only have the Solaris documentation,
> and that's for an independent implementation.
Yes, for LD_AUDIT it is underdocumented, here we have only the linux
man pages project pages.
>> Existing tooling to process such relocations and entries could
>> remain unchanged and we would continue to support LD_AUDIT.
>
> My understanding is that H.J.'s proposal requires changes when running
> in non-audit mode. It certainly requires relinking all binaries,
> perhaps even with special flags.
It would require a relink only to fix existing binaries which are broken
by the use of -fno-plt, which is not an option that has seen general use
anywhere that I am aware of.
> Using ld.so-generated thunks for all GLOB_DAT function symbol
> relocations would happen in audit mode only and should work with
> existing binaries which were built with -Wl,-z,now.
This is a very good reason to prefer one method over another, that we
could fix existing binaries. However, I still think the complexity of
such a fix outweighs what we are trying to fix. Do we have another use
for such stubs?
Today we have to admit that -fno-plt is not compatible with auditing.
I would like to change that to ensure that in future releases we are
able to let users use -fno-plt *and* auditing.
Cheers,
Carlos.
next prev parent reply other threads:[~2018-03-22 15:36 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-01 0:00 H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` Carlos O'Donell [this message]
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Florian Weimer
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Carlos O'Donell
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Alan Modra
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Alan Modra
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` H.J. Lu
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` Cary Coutant
2018-01-01 0:00 ` H.J. Lu
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