linux-kernel - Re: [PATCH 2/2] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned

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Message-ID: <20230526115426.k64df56qywql5mel@box.shutemov.name>
Date:   Fri, 26 May 2023 14:54:26 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     dave.hansen@...el.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, decui@...rosoft.com, rick.p.edgecombe@...el.com,
        seanjc@...gle.com, thomas.lendacky@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/tdx: Fix race between set_memory_encrypted() and
 load_unaligned_zeropad()

On Thu, May 25, 2023 at 04:40:00PM -0700, Sathyanarayanan Kuppuswamy wrote:
> Hi, 
> 
> On 5/25/23 3:58 PM, Kirill A. Shutemov wrote:
> > Touching privately mapped GPA that is not properly converted to private
> > with MapGPA and accepted leads to unrecoverable exit to VMM.
> > 
> > load_unaligned_zeropad() can touch memory that is not owned by the
> > caller, but just happened to next after the owned memory.
> > This load_unaligned_zeropad() behaviour makes it important when kernel
> > asks VMM to convert a GPA from shared to private or back. Kernel must
> > never have a page mapped into direct mapping (and aliases) as private
> > when the GPA is already converted to shared or when GPA is not yet
> > converted to private.
> > 
> > guest.enc_status_change_prepare() called before adjusting direct mapping
> > and therefore it is responsible for converting the memory to private.
> > 
> > guest.enc_tlb_flush_required() called after adjusting direct mapping and
> > it converts the memory to shared.
> 
> Do you mean .enc_status_change_finish() here? Isn't enc_tlb_flush_required()
> called before adjusting the mapping?

Yes, I copy-pasted wrong callback :/

-- 
  Kiryl Shutsemau / Kirill A. Shutemov