linux-kernel - Re: [PATCH v5 09/32] x86/mm: Provide general kernel support for memory encryption

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Message-ID: <9fc79e28-ad64-1c2f-4c46-a4efcdd550b0@amd.com>
Date:   Mon, 24 Apr 2017 10:53:58 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dave Hansen <dave.hansen@...el.com>, <linux-arch@...r.kernel.org>,
        <linux-efi@...r.kernel.org>, <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <x86@...nel.org>,
        <kexec@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>
CC:     Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 09/32] x86/mm: Provide general kernel support for
 memory encryption

On 4/21/2017 4:52 PM, Dave Hansen wrote:
> On 04/18/2017 02:17 PM, Tom Lendacky wrote:
>> @@ -55,7 +57,7 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
>>  	__phys_addr_symbol(__phys_reloc_hide((unsigned long)(x)))
>>
>>  #ifndef __va
>> -#define __va(x)			((void *)((unsigned long)(x)+PAGE_OFFSET))
>> +#define __va(x)			((void *)(__sme_clr(x) + PAGE_OFFSET))
>>  #endif
>
> It seems wrong to be modifying __va().  It currently takes a physical
> address, and this modifies it to take a physical address plus the SME bits.

This actually modifies it to be sure the encryption bit is not part of
the physical address.

>
> How does that end up ever happening?  If we are pulling physical
> addresses out of the page tables, we use p??_phys().  I'd expect *those*
> to be masking off the SME bits.
>
> Is it these cases?
>
> 	pgd_t *base = __va(read_cr3());
>
> For those, it seems like we really want to create two modes of reading
> cr3.  One that truly reads CR3 and another that reads the pgd's physical
> address out of CR3.  Then you only do the SME masking on the one
> fetching a physical address, and the SME bits never leak into __va().

I'll investigate this and see if I can remove the mod to __va().

Thanks,
Tom

>