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

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 0c64026a0951cb53ede82c46c4838525e059ab6e..ce34a05ccdc4831ada4aecba9423ad05c57b02c0 100644 (file)
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -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;