x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB

The current randomization granularity of 5-level is 512 GB. The mapping of
the real mode trampoline has been reduced to one PUD entry, so there is no
restriction anymore.

Reduce the granularity to 1GB for 5-level paging mode which allows better
randomization.

[ tglx: Massaged changelog ]

Signed-off-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: dave.hansen@linux.intel.com
Cc: luto@kernel.org
Cc: peterz@infradead.org
Cc: bp@alien8.de
Cc: hpa@zytor.com
Cc: keescook@chromium.org
Cc: thgarnie@google.com
Link: https://lkml.kernel.org/r/20190308025616.21440-3-bhe@redhat.com

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 9781375..f6ba279 100644 (file)
--- 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;
        }
 }