linux-kernel - [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size

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Date:   Wed, 29 Aug 2018 10:17:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     tglx@...utronix.de, mingo@...nel.org, hpa@...or.com,
        thgarnie@...gle.com, kirill.shutemov@...ux.intel.com
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH 1/2] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size

In memory KASLR, __PHYSICAL_MASK_SHIFT is taken to calculate the
initial size of the direct mapping region. This is right in the
old code where __PHYSICAL_MASK_SHIFT was equal to MAX_PHYSMEM_BITS,
46bit, and only 4-level mode was supported.

Later, in commit:
b83ce5ee91471d ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52"),
__PHYSICAL_MASK_SHIFT was changed to be 52 always, no matter it's
5-level or 4-level. This is wrong for 4-level paging. Then when
adapt phyiscal memory region size based on available memory, it
will overflow if the amount of system RAM and the padding is bigger
than 64TB.

In fact, here MAX_PHYSMEM_BITS should be used instead. Fix it by
by replacing __PHYSICAL_MASK_SHIFT with MAX_PHYSMEM_BITS.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 arch/x86/mm/kaslr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 61db77b0eda9..0988971069c9 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -93,7 +93,7 @@ void __init kernel_randomize_memory(void)
 	if (!kaslr_memory_enabled())
 		return;

-	kaslr_regions[0].size_tb = 1 << (__PHYSICAL_MASK_SHIFT - TB_SHIFT);
+	kaslr_regions[0].size_tb = 1 << (MAX_PHYSMEM_BITS - TB_SHIFT);
 	kaslr_regions[1].size_tb = VMALLOC_SIZE_TB;

 	/*
-- 
2.13.6