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[v4,2/2] x86/KASLR: Increase BRK pages for KASLR memory randomization

Message ID 1470762665-88032-2-git-send-email-thgarnie@google.com
State New, archived
Headers show

Commit Message

Thomas Garnier Aug. 9, 2016, 5:11 p.m. UTC
Default implementation expects 6 pages maximum are needed for low page
allocations. If KASLR memory randomization is enabled, the worse case
of e820 layout would require 12 pages (no large pages). It is due to the
PUD level randomization and the variable e820 memory layout.

This bug was found while doing extensive testing of KASLR memory
randomization on different type of hardware.

Fixes: 021182e52fe0 ("Enable KASLR for physical mapping memory regions")
Signed-off-by: Thomas Garnier <thgarnie@google.com>
Based on next-20160805
 arch/x86/mm/init.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)
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diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 6209289..796e7af 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -122,8 +122,18 @@  __ref void *alloc_low_pages(unsigned int num)
 	return __va(pfn << PAGE_SHIFT);
-/* need 3 4k for initial PMD_SIZE,  3 4k for 0-ISA_END_ADDRESS */
+ * By default need 3 4k for initial PMD_SIZE,  3 4k for 0-ISA_END_ADDRESS.
+ * With KASLR memory randomization, depending on the machine e820 memory
+ * and the PUD alignment. We may need twice more pages when KASLR memory
+ * randomization is enabled.
+ */
+#define INIT_PGD_PAGE_COUNT      6
+#define INIT_PGD_PAGE_COUNT      12
 RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE);
 void  __init early_alloc_pgt_buf(void)