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    SubjectRe: [PATCH v2 1/3] x86/mm/KASLR: Fix the wrong calculation of kalsr region initial size
    On 09/10/18 at 08:18am, Ingo Molnar wrote:
    >
    > * Baoquan He <bhe@redhat.com> wrote:
    >
    > > 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.
    >......
    > - what does 'memory KASLR' mean? All KASLR deals with memory.

    Thanks for your reviewing. I have updated patch log according to your
    comments. For this one, Thomas Garnier calls it memory section KASLR, to
    differentiate with kernel text KASLR. I would like to call it memory region
    KASLR, is it OK?

    Paste the updated patch here.


    From df0df638a24aafeee6862f184769c4fb96f29afb Mon Sep 17 00:00:00 2001
    From: Baoquan He <bhe@redhat.com>
    Date: Fri, 29 Jun 2018 09:43:28 +0800
    Subject: [PATCH] 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.

    Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Reviewed-by: Thomas Garnier <thgarnie@google.com>
    Signed-off-by: Baoquan He <bhe@redhat.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


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