linux-kernel - [PATCH v3 4/6] x86/mm/KASLR: Fix the wrong calculation of memory region initial size

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Date:   Sat, 16 Feb 2019 22:00:06 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        x86@...nel.org, travis@....com, thgarnie@...gle.com,
        keescook@...omium.org, akpm@...ux-foundation.org,
        yamada.masahiro@...ionext.com, kirill@...temov.name,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH v3 4/6] x86/mm/KASLR: Fix the wrong calculation of memory region initial size

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.

Fixes: b83ce5ee9147 ("x86/mm/64: Make __PHYSICAL_MASK_SHIFT always 52")
Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Reviewed-by: Thomas Garnier <thgarnie@...gle.com>
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 bf680929fe26..97768df923e3 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -137,7 +137,7 @@ 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