Commit eb38be6d authored Jul 28, 2020 by Arvind Sankar Committed by Ingo Molnar Jul 31, 2020

x86/kaslr: Drop unnecessary alignment in find_random_virt_addr()



Drop unnecessary alignment of image_size to CONFIG_PHYSICAL_ALIGN in
find_random_virt_addr, it cannot change the result: the largest valid
slot is the largest n that satisfies

  minimum + n * CONFIG_PHYSICAL_ALIGN + image_size <= KERNEL_IMAGE_SIZE

(since minimum is already aligned) and so n is equal to

  (KERNEL_IMAGE_SIZE - minimum - image_size) / CONFIG_PHYSICAL_ALIGN

even if image_size is not aligned to CONFIG_PHYSICAL_ALIGN.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200728225722.67457-17-nivedita@alum.mit.edu

parent 46a5b29a

arch/x86/boot/compressed/kaslr.c

+1 −5

Original line number	Diff line number	Diff line
		@@ -825,16 +825,12 @@ static unsigned long find_random_virt_addr(unsigned long minimum,
		{
		unsigned long slots, random_addr;

		/* Align image_size for easy slot calculations. */
		image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);

		/*
		* There are how many CONFIG_PHYSICAL_ALIGN-sized slots
		* that can hold image_size within the range of minimum to
		* KERNEL_IMAGE_SIZE?
		*/
		slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
		CONFIG_PHYSICAL_ALIGN + 1;
		slots = 1 + (KERNEL_IMAGE_SIZE - minimum - image_size) / CONFIG_PHYSICAL_ALIGN;

		random_addr = kaslr_get_random_long("Virtual") % slots;

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