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    SubjectRe: [RFC PATCH v7 05/16] arm64/mm: Add support for XPFO
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    On 2/12/19 1:01 PM, Laura Abbott wrote:
    > On 2/12/19 7:52 AM, Khalid Aziz wrote:
    >> On 1/23/19 7:24 AM, Konrad Rzeszutek Wilk wrote:
    >>> On Thu, Jan 10, 2019 at 02:09:37PM -0700, Khalid Aziz wrote:
    >>>> From: Juerg Haefliger <juerg.haefliger@canonical.com>
    >>>>
    >>>> Enable support for eXclusive Page Frame Ownership (XPFO) for arm64 and
    >>>> provide a hook for updating a single kernel page table entry (which is
    >>>> required by the generic XPFO code).
    >>>>
    >>>> v6: use flush_tlb_kernel_range() instead of __flush_tlb_one()
    >>>>
    >>>> CC: linux-arm-kernel@lists.infradead.org
    >>>> Signed-off-by: Juerg Haefliger <juerg.haefliger@canonical.com>
    >>>> Signed-off-by: Tycho Andersen <tycho@docker.com>
    >>>> Signed-off-by: Khalid Aziz <khalid.aziz@oracle.com>
    >>>> ---
    >>>>   arch/arm64/Kconfig     |  1 +
    >>>>   arch/arm64/mm/Makefile |  2 ++
    >>>>   arch/arm64/mm/xpfo.c   | 58
    >>>> ++++++++++++++++++++++++++++++++++++++++++
    >>>>   3 files changed, 61 insertions(+)
    >>>>   create mode 100644 arch/arm64/mm/xpfo.c
    >>>>
    >>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    >>>> index ea2ab0330e3a..f0a9c0007d23 100644
    >>>> --- a/arch/arm64/Kconfig
    >>>> +++ b/arch/arm64/Kconfig
    >>>> @@ -171,6 +171,7 @@ config ARM64
    >>>>       select SWIOTLB
    >>>>       select SYSCTL_EXCEPTION_TRACE
    >>>>       select THREAD_INFO_IN_TASK
    >>>> +    select ARCH_SUPPORTS_XPFO
    >>>>       help
    >>>>         ARM 64-bit (AArch64) Linux support.
    >>>>   diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
    >>>> index 849c1df3d214..cca3808d9776 100644
    >>>> --- a/arch/arm64/mm/Makefile
    >>>> +++ b/arch/arm64/mm/Makefile
    >>>> @@ -12,3 +12,5 @@ KASAN_SANITIZE_physaddr.o    += n
    >>>>     obj-$(CONFIG_KASAN)        += kasan_init.o
    >>>>   KASAN_SANITIZE_kasan_init.o    := n
    >>>> +
    >>>> +obj-$(CONFIG_XPFO)        += xpfo.o
    >>>> diff --git a/arch/arm64/mm/xpfo.c b/arch/arm64/mm/xpfo.c
    >>>> new file mode 100644
    >>>> index 000000000000..678e2be848eb
    >>>> --- /dev/null
    >>>> +++ b/arch/arm64/mm/xpfo.c
    >>>> @@ -0,0 +1,58 @@
    >>>> +/*
    >>>> + * Copyright (C) 2017 Hewlett Packard Enterprise Development, L.P.
    >>>> + * Copyright (C) 2016 Brown University. All rights reserved.
    >>>> + *
    >>>> + * Authors:
    >>>> + *   Juerg Haefliger <juerg.haefliger@hpe.com>
    >>>> + *   Vasileios P. Kemerlis <vpk@cs.brown.edu>
    >>>> + *
    >>>> + * This program is free software; you can redistribute it and/or
    >>>> modify it
    >>>> + * under the terms of the GNU General Public License version 2 as
    >>>> published by
    >>>> + * the Free Software Foundation.
    >>>> + */
    >>>> +
    >>>> +#include <linux/mm.h>
    >>>> +#include <linux/module.h>
    >>>> +
    >>>> +#include <asm/tlbflush.h>
    >>>> +
    >>>> +/*
    >>>> + * Lookup the page table entry for a virtual address and return a
    >>>> pointer to
    >>>> + * the entry. Based on x86 tree.
    >>>> + */
    >>>> +static pte_t *lookup_address(unsigned long addr)
    >>>> +{
    >>>> +    pgd_t *pgd;
    >>>> +    pud_t *pud;
    >>>> +    pmd_t *pmd;
    >>>> +
    >>>> +    pgd = pgd_offset_k(addr);
    >>>> +    if (pgd_none(*pgd))
    >>>> +        return NULL;
    >>>> +
    >>>> +    pud = pud_offset(pgd, addr);
    >>>> +    if (pud_none(*pud))
    >>>> +        return NULL;
    >>>> +
    >>>> +    pmd = pmd_offset(pud, addr);
    >>>> +    if (pmd_none(*pmd))
    >>>> +        return NULL;
    >>>> +
    >>>> +    return pte_offset_kernel(pmd, addr);
    >>>> +}
    >>>> +
    >>>> +/* Update a single kernel page table entry */
    >>>> +inline void set_kpte(void *kaddr, struct page *page, pgprot_t prot)
    >>>> +{
    >>>> +    pte_t *pte = lookup_address((unsigned long)kaddr);
    >>>> +
    >>>> +    set_pte(pte, pfn_pte(page_to_pfn(page), prot));
    >>>
    >>> Thought on the other hand.. what if the page is PMD? Do you really want
    >>> to do this?
    >>>
    >>> What if 'pte' is NULL?
    >>>> +}
    >>>> +
    >>>> +inline void xpfo_flush_kernel_tlb(struct page *page, int order)
    >>>> +{
    >>>> +    unsigned long kaddr = (unsigned long)page_address(page);
    >>>> +    unsigned long size = PAGE_SIZE;
    >>>> +
    >>>> +    flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
    >>>
    >>> Ditto here. You are assuming it is PTE, but it may be PMD or such.
    >>> Or worts - the lookup_address could be NULL.
    >>>
    >>>> +}
    >>>> -- 
    >>>> 2.17.1
    >>>>
    >>
    >> Hi Konrad,
    >>
    >> This makes sense. x86 version of set_kpte() checks pte for NULL and also
    >> checks if the page is PMD. Now what you said about adding level to
    >> lookup_address() for arm makes more sense.
    >>
    >> Can someone with knowledge of arm64 mmu make recommendations here?
    >>
    >> Thanks,
    >> Khalid
    >>
    >
    > arm64 can't split larger pages and requires everything must be
    > mapped as pages (see [RFC PATCH v7 08/16] arm64/mm: disable
    > section/contiguous mappings if XPFO is enabled) . Any
    > situation where we would get something other than a pte
    > would be a bug.

    Thanks, Laura! That helps a lot. I would think checking for NULL pte in
    set_kpte() would still make sense since lookup_address() can return
    NULL. Something like:

    --- arch/arm64/mm/xpfo.c 2019-01-30 13:36:39.857185612 -0700
    +++ arch/arm64/mm/xpfo.c.new 2019-02-12 13:26:47.471633031 -0700
    @@ -46,6 +46,11 @@
    {
    pte_t *pte = lookup_address((unsigned long)kaddr);

    + if (unlikely(!pte)) {
    + WARN(1, "xpfo: invalid address %p\n", kaddr);
    + return;
    + }
    +
    set_pte(pte, pfn_pte(page_to_pfn(page), prot));
    }

    --
    Khalid[unhandled content-type:application/pgp-keys]
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