Re: RFC: Audit external function called indirectly via GOT

[Florian Weimer <fw@deneb.enyo.de>]

* H. J. Lu:

> On Thu, Mar 22, 2018 at 9:47 AM, Florian Weimer <fw@deneb.enyo.de> wrote:
>> * Carlos O'Donell:
>>
>>> 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.
>>
>> Thanks, I didn't know that.
>>
>>>> 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.
>>
>> I don't think that's actually true.  BFD ld has not emitted
>> R_X86_64_JUMP_SLOT relocations with -z now for quite some time now.
>> This optimization predates -fno-plt.
>>
>
> Not true with binutils 2.30:
>
> [hjl@gnu-bdx-1 include]$ readelf -d /bin/ld | grep NOW
>  0x0000000000000018 (BIND_NOW)
>  0x000000006ffffffb (FLAGS_1)            Flags: NOW PIE
> [hjl@gnu-bdx-1 include]$ readelf -rW /bin/ld | grep JUMP_SLOT
> 00000000001b0868  0000000100000007 R_X86_64_JUMP_SLOT
> 0000000000000000 getenv@GLIBC_2.2.5 + 0
> ...

But binutils 2.28 or some earlier version exhibited different
behavior, right?