[PATCH] [PR libc/18801] PIE binary with STT_GNU_IFUNC symbol and TEXTREL segfaults on x86_64

[Sriraman Tallam]

On Tue, Aug 11, 2015 at 5:02 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Aug 11, 2015 at 3:57 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> On Tue, Aug 11, 2015 at 3:54 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Tue, Aug 11, 2015 at 3:37 PM, Paul Pluzhnikov <ppluzhnikov@google.com> wrote:
>>>> On Tue, Aug 11, 2015 at 3:31 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>>> No.  I am proposing that linker issues an error if there is TEXTREL
>>>>> with IFUNC unless "-z now'" is used, assuming that this doesn't
>>>>> require changes to ld.so nor SELinux.
>>>>
>>>> Ah, ok. But that *doesn't* help current crash at all: "-z now" will
>>>> force IFUNC resolver (if any) to be called, and that call will fail
>>>> since we are currently removing execute protections.
>>>> (This is in fact the situation we've discovered the crash in originally.)
>>>
>>> Can you try adding  -Wl,-z,execstack?
>>
>> Yes, making the stack executable will solve the problem.  My test case
>> needed ".note.GNU-stack" specifically for this.
>
> Given SELinux issue, I don't think we should change ld.so.  Instead,
> we can change ld to issue an error for TEXTREL with IFUNC and
> suggest -fPIE and  -Wl,-z,execstack as workaround.

I am not sure I understand the problem.  What is wrong with the patch?
 Why should IFUNC+TEXTREL be disallowed?

Thanks
Sri


>
>
> --
> H.J.