Re: [PATCH] mm: fix RODATA_TEST failure "rodata_test: test data was not read only"

[Kees Cook]

On Mon, Sep 25, 2017 at 12:41 PM, Segher Boessenkool
<segher@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Sep 25, 2017 at 04:01:55PM +0000, David Laight wrote:
>> From: Segher Boessenkool
>> > The compiler puts this item in .sdata, for 32-bit.  There is no .srodata,
>> > so if it wants to use a small data section, it must use .sdata .
>> >
>> > Non-external, non-referenced symbols are not put in .sdata, that is the
>> > difference you see with the "static".
>> >
>> > I don't think there is a bug here.  If you think there is, please open
>> > a GCC bug.
>>
>> The .sxxx sections are for 'small' data that can be accessed (typically)
>> using small offsets from a global register.
>> This means that all sections must be adjacent in the image.
>> So you can't really have readonly small data.
>>
>> My guess is that the linker script is putting .srodata in with .sdata.
>
> .srodata does not *exist* (in the ABI).

So, I still think this is a bug. The variable is marked const: this is
not a _suggestion_. :) If the compiler produces output where the
variable is writable, that's a bug.

I can't tell if this bug is related:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=9571

-Kees

-- 
Kees Cook
Pixel Security