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x86/kaslr: Drop unnecessary alignment in find_random_virt_addr()

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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
This commit is contained in:
Arvind Sankar 2020-07-28 18:57:17 -04:00 committed by Ingo Molnar
parent 46a5b29a4a
commit eb38be6db5
1 changed files with 1 additions and 5 deletions
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6
arch/x86/boot/compressed/kaslr.c
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@ -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;