Messages in this thread | | | From | Arvind Sankar <> | Date | Tue, 28 Jul 2020 15:45:11 -0400 | Subject | Re: [PATCH v2 6/8] x86/kaslr: Simplify process_gb_huge_pages |
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On Tue, Jul 28, 2020 at 12:27:17PM -0700, Kees Cook wrote: > On Mon, Jul 27, 2020 at 07:07:59PM -0400, Arvind Sankar wrote: > > Short-circuit the whole function on 32-bit. > > > > Replace the loop to determine the number of 1Gb pages with arithmetic. > > > > Fix one minor bug: if the end of the region is aligned on a 1Gb > > boundary, the current code will not use the last available 1Gb page due > > to an off-by-one error. > > > > Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu> > > Can you add some KUnit tests could be written to do validation of the > refactorings? Touching this code is so painful. :) > > -Kees
Can I try to do that later -- I've never written a KUnit test, though it's probably a good opportunity to learn how to do one.
> > > +++ b/arch/x86/boot/compressed/kaslr.c > > @@ -546,49 +546,43 @@ static void store_slot_info(struct mem_vector *region, unsigned long image_size) > > static void > > process_gb_huge_pages(struct mem_vector *region, unsigned long image_size) > > { > > - unsigned long addr, size = 0; > > + unsigned long pud_start, pud_end, gb_huge_pages; > > struct mem_vector tmp; > > - int i = 0; > > > > - if (!max_gb_huge_pages) { > > + if (IS_ENABLED(CONFIG_X86_32) || !max_gb_huge_pages) { > > store_slot_info(region, image_size); > > return; > > } > > Won't max_gb_huge_pages always be false for 32-bit? > > -- > Kees Cook
It will, assuming someone doesn't pass bogus command-line arguments to reserve Gb pages on 32-bit.
But the IS_ENABLED check allows the compiler to eliminate the entire function at compile time.
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