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Subject: Re: [RFC PATCH v7 05/16] arm64/mm: Add support for XPFO
To:     Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc:     juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de,
        ak@linux.intel.com, torvalds@linux-foundation.org,
        liran.alon@oracle.com, keescook@google.com,
        Juerg Haefliger <juerg.haefliger@canonical.com>,
        deepa.srinivasan@oracle.com, chris.hyser@oracle.com,
        tyhicks@canonical.com, dwmw@amazon.co.uk,
        andrew.cooper3@citrix.com, jcm@redhat.com,
        boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com,
        joao.m.martins@oracle.com, jmattson@google.com,
        pradeep.vincent@oracle.com, john.haxby@oracle.com,
        tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de,
        steven.sistare@oracle.com, kernel-hardening@lists.openwall.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        Tycho Andersen <tycho@docker.com>
References: <cover.1547153058.git.khalid.aziz@oracle.com>
 <89f03091af87f5ab27bd6cafb032236d5bd81d65.1547153058.git.khalid.aziz@oracle.com>
 <20190123142410.GC19289@Konrads-MacBook-Pro.local>
From:   Khalid Aziz <khalid.aziz@oracle.com>
Organization: Oracle Corp
Message-ID: <4dfba458-1bf6-25ff-df4c-b96a1221cd95@oracle.com>
Date:   Tue, 12 Feb 2019 08:52:51 -0700
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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.
>> =20
>> 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	+=3D n
>> =20
>>  obj-$(CONFIG_KASAN)		+=3D kasan_init.o
>>  KASAN_SANITIZE_kasan_init.o	:=3D n
>> +
>> +obj-$(CONFIG_XPFO)		+=3D 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 modi=
fy it
>> + * under the terms of the GNU General Public License version 2 as pub=
lished 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 poi=
nter 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 =3D pgd_offset_k(addr);
>> +	if (pgd_none(*pgd))
>> +		return NULL;
>> +
>> +	pud =3D pud_offset(pgd, addr);
>> +	if (pud_none(*pud))
>> +		return NULL;
>> +
>> +	pmd =3D 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 =3D lookup_address((unsigned long)kaddr);
>> +
>> +	set_pte(pte, pfn_pte(page_to_pfn(page), prot));
>=20
> Thought on the other hand.. what if the page is PMD? Do you really want=

> to do this?
>=20
> What if 'pte' is NULL?
>> +}
>> +
>> +inline void xpfo_flush_kernel_tlb(struct page *page, int order)
>> +{
>> +	unsigned long kaddr =3D (unsigned long)page_address(page);
>> +	unsigned long size =3D PAGE_SIZE;
>> +
>> +	flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
>=20
> Ditto here. You are assuming it is PTE, but it may be PMD or such.
> Or worts - the lookup_address could be NULL.
>=20
>> +}
>> --=20
>> 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

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