On Thu, Jan 28, 2016 at 06:06:53AM -0800, Kees Cook wrote:
> On Thu, Jan 28, 2016 at 3:06 AM, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> > One thing I would like to do is to avoid the need for fixup_executable
> > entirely, by mapping the kernel text RO from the outset. However, that
> > requires rework of the alternatives patching (to use a temporary RW
> > alias), and I haven't had the time to look into that yet.
>
> This makes perfect sense for the rodata section, but the (future)
> postinit_rodata section we'll still want to mark RO after init
> finishes. x86 and ARM cheat by marking both RO after init, and they
> don't have to pad sections. parisc will need to solve this too.
Depending on how many postinit_rodata variables there are, we might be
able to drop those in .rodata, have them RO always, and initialise them
via a temporary RW alias (e.g. something in the vmalloc area).
The only requirement for that is that we use a helper to initialise any
__postinit_ro variables via a temporary RW alias, e.g.
#define SET_POST_INIT_RO(ptr, v) ({ \\
typeof(ptr) __ptr_rw = (ptr) \\
BUG_ON(initcalls_done); \\
__ptr_rw = create_rw_alias(__ptr); \\
__ptr_rw = v; \\
destroy_rw_alias(__ptr_rw); \\
})
...
__postinit_ro void *thing;
void __init some_init_func(void) {
void *__thing = some_ranodomized_allocator();
SET_POSTINIT_RO(thing, thing);
}
Mark.
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