Messages in this thread | | | Date | Thu, 28 Jan 2016 14:59:01 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: make CONFIG_DEBUG_RODATA non-optional |
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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@arm.com> 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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