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

[tip-bot for Baoquan He <tipbot@zytor.com>]

Commit-ID:  b569c18434987163a05f05a12cdf6a9975c55ff3
Gitweb:     https://git.kernel.org/tip/b569c18434987163a05f05a12cdf6a9975c55ff3
Author:     Baoquan He <bhe@redhat.com>
AuthorDate: Fri, 8 Mar 2019 10:56:16 +0800
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Fri, 5 Apr 2019 22:13:52 +0200

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
---
 arch/x86/mm/kaslr.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 97813751340d..f6ba2791eeb5 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;
 	}
 }