On Mon, Feb 20, 2017 at 4:45 AM, Mark Rutland <mark.rutl...@arm.com> wrote: > On Sun, Feb 19, 2017 at 11:35:51AM +0000, Ard Biesheuvel wrote: >> On 19 February 2017 at 10:04, Hoeun Ryu <hoeun....@gmail.com> wrote: >> > Map rodata sections seperately for the new __ro_mostly_after_init section. >> > Attribute of memory for __ro_mostly_after_init section can be changed later >> > so we need a dedicated vmalloced region for set_memory_rw/ro api. > >> While it is correct that you are splitting this into three separate >> segments (otherwise we would not be able to change the permissions >> later without risking splitting to occur), I think this leads to >> unnecessary fragmentation. >> >> If there is demand for this feature (but you still need to make the >> argument for that), I wonder if it wouldn't be sufficient, and much >> more straightforward, to redefine the __ro_after_init semantics to >> include the kind of subsystem registration and module init context you >> are targeting, and implement some hooks to temporarily lift the >> __ro_after_init r/o permission restrictions in a controlled manner. > > From a look over the series, I think this is just __write_rarely in > disguise. I personally think that we should keep __write_rarely and > __ro_after_init separate, the later being a strictly one-shot affair.
That's my thinking too. > I had some ideas [1] as to how we could implement __write_rarely without > carving up the kernel mapping further (and keeping the RW permissions > local to the thread needing it), but I have not had the time to look > into that further. I'm working on a series to do this for x86, but I keep getting distracted. I hope to get an RFC posted this week. -Kees -- Kees Cook Pixel Security
