[PATCH v3 2/2] x86/mm/KASLR: Change the granularity of randomization to PUD size in 5-level

[Baoquan He]

The current randomization granularity of 5-level is 512 GB. Improve
it to 1 GB. This can add more randomness to memory region KASLR in
5-level paging mode

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
 arch/x86/mm/kaslr.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 8bd4192c68b9..9a8756517504 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -125,10 +125,7 @@ void __init kernel_randomize_memory(void)
 		 */
 		entropy = remain_entropy / (ARRAY_SIZE(kaslr_regions) - i);
 		prandom_bytes_state(&rand_state, &rand, sizeof(rand));
-		if (pgtable_l5_enabled())
-			entropy = (rand % (entropy + 1)) & P4D_MASK;
-		else
-			entropy = (rand % (entropy + 1)) & PUD_MASK;
+		entropy = (rand % (entropy + 1)) & PUD_MASK;
 		vaddr += entropy;
 		*kaslr_regions[i].base = vaddr;
 
@@ -137,10 +134,7 @@ void __init kernel_randomize_memory(void)
 		 * randomization alignment.
 		 */
 		vaddr += get_padding(&kaslr_regions[i]);
-		if (pgtable_l5_enabled())
-			vaddr = round_up(vaddr + 1, P4D_SIZE);
-		else
-			vaddr = round_up(vaddr + 1, PUD_SIZE);
+		vaddr = round_up(vaddr + 1, PUD_SIZE);
 		remain_entropy -= entropy;
 	}
 }
@@ -197,8 +191,8 @@ static void __meminit init_trampoline_pud(void)
  * that area. In case KASLR disabled, the 1st PGD entry of the
  * direct mapping is copied directly. If KASLR is enabled, only
  * copy the 1st PUD entry where physical address 0 resides since
- * the granularity of randomization is PUD size in 4-level, and
- * P4D size in 5-level.
+ * the granularity of randomization is PUD size in both 4-level and
+ * 5-level.
  *
  * This consumes one low memory page in 4-level case, and extra one
  * in 5-level.
-- 
2.17.2