Kernel warns of executable stack

[Markus Gothe]

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

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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