Re: set_memory_* (was: Re: BUG: unable to handle kernel paging request in bpf_int_jit_compile)

[Kees Cook]

On Tue, Jun 26, 2018 at 3:53 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
> In any case, for pairs like set_memory_ro() + set_memory_rw() that are also used
> outside of bpf e.g. STRICT_MODULE_RWX and friends which are mostly default these
> days for some archs, is the choice to not check errors from there by design or from
> historical context that it originated from 'debugging code' in that sense (DEBUG_RODATA /
> DEBUG_SET_MODULE_RONX) earlier? Also if no-one checks for errors (and if that would
> infact be the recommendation it is agreed upon) should the API be changed to void,
> or generally should actual error checking occur on these + potential rollback; but
> then question is what about restoring part from prior set_memory_ro() via set_memory_rw()?
> Kees/others, do you happen to have some more context on recommended use around this
> by any chance? (Would probably also help if we add some doc around assumptions into
> include/linux/set_memory.h for future users.)

If set_memory_* can fail, I think it needs to be __must_check, and all
the callers need to deal with it gracefully. Those markings aren't
"advisory": they're expected to actually do what they say.

-Kees

-- 
Kees Cook
Pixel Security