[PATCH v4 4/6] x86/mm/KASLR: Fix the wrong calculation of memory region initial size

[Baoquan He]

In memory region KASLR, __PHYSICAL_MASK_SHIFT is taken to calculate
the initial size of the direct mapping region. This is correct in
the old code where __PHYSICAL_MASK_SHIFT was equal to MAX_PHYSMEM_BITS,
46 bits, 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 always 52 bits, no matter it's
5-level or 4-level. This is wrong for 4-level paging. Then when we
adapt physical memory region size based on available memory, it
will overflow if the amount of system RAM and the padding is bigger
than 64 TB.

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

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 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 d7ea6b252594..ebf6d1d92385 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -131,7 +131,7 @@ 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;
 
 	/*
-- 
2.17.2