Kernel warns of executable stack

[Markus Gothe]

It's not required per se for an application.

But you would need to relink your binaries with '-z,noexecstack' to turn
it off.

//M

On 2020-04-24 00:25, Chris Packham wrote:
> On Fri, 2020-04-24 at 00:08 +0200, Markus Gothe wrote:
>> Background: The executable stack is needed for MIPS and the FPU
>> (which
>> decodes any unknown instruction as well).
>>
>> There have been some patches floating around to fix this behavior
>> since
>> Linux 3.12 so probably that's why you didn't notice before upgrading.
>>
>> The 'dc' applet at least requires an executable stack and might be
>> why
>> it is triggered. (Did get a MIPS32-kernel to go crash with 'bad
>> stack'
>> when running dc -e '4 0 / p' however it's fixed in 1.31.0).
>>
>> //M
> OK and I can confirm that I do get the error message on mips64 and
> mips32 (I just failed to notice in my automated test output).
>
> So executable stack is required for floating point on mips? Should I
> send a kernel patch to add  && !IS_ENABLED(CONFIG_MIPS) to the warning?
>
>> On 2020-04-23 23:39, Chris Packham wrote:
>>> On Thu, 2020-04-23 at 07:29 +0200, Christophe Leroy wrote:
>>>> Hi,
>>>>
>>>> Christophe
>>>>
>>>> Le 23/04/2020 à 03:13, Chris Packham a écrit :
>>>>> Hi,
>>>>>
>>>>> I'm just in the process of updating our products to Linux v5.6
>>>>> and
>>>>> one
>>>>> of them produces a new warning message from the kernel about
>>>>> busybox
>>>>> (v1.31.1)
>>>>>
>>>>>    kernel: process '/bin/busybox' started with executable stack
>>>> Got similar discussion about klibc 2 monthes ago, look at 
>>>> https://lists.zytor.com/archives/klibc/2020-February/004271.html
>>>>
>>>>> The target in question is a mips64 (octeon3). We have other
>>>>> targets
>>>>> (mips32, armv7, ppc32, ppc64) which don't complain.
>>>>>
>>>>> Some searching led me to
>>>>>
>>>>> https://lore.kernel.org/lkml/20191208171918.GC19716@avx2/
>>>>>
>>>>> Which suggests I should be filing a bug report with the vendor
>>>>> so
>>>>> here
>>>>> I am.
>>>> Did you have a look into busybox bugzilla ? 
>>>> https://bugs.busybox.net/
>>> I did a quick search of the mailing list didn't spot anything
>>> yesterday.
>>>
>>> Just now I did find https://bugs.busybox.net/show_bug.cgi?id=12801
>>> which is in the ball-park. It points at uclibc + binutils 2.31. I'm
>>> using GNU libc and binutils 2.32.
>>>
>>>>> Here's some readelf output from the binary
>>>> Can you perform "objdump -x " on your binary ?
>>>>
>>> The output is quite large so I'll link to it instead of including
>>> it
>>> in-line.
>>>
>>> https://gist.github.com/cpackham/48eeab4b8801a57ef737e3fda265cae7
>>>
>>> Interestingly I can't see anything rwx or RWE in either output
>>>
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