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Subject[PATCH v2 1/3] 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

Fixes: b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52")
Signed-off-by: Baoquan He <>
Acked-by: Kirill A. Shutemov <>
Reviewed-by: Thomas Garnier <>
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())

- 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;

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