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Subject[PATCH v2 2/2] x86/mm/KASLR: Change the granularity of randomization to PUD size in 5-level
Date
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@redhat.com>
---
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 131e08a10a68..99ec75634613 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -204,10 +204,7 @@ 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;

@@ -216,10 +213,7 @@ void __init kernel_randomize_memory(void)
* randomization alignment.
*/
vaddr += kaslr_regions[i].size_tb << TB_SHIFT;
- 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;
}
}
@@ -276,8 +270,8 @@ 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
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