linux-kernel - Re: [PATCHv2 2/3] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned

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Message-ID: <7e0e7074-4bc7-3f39-27df-623448044c72@intel.com>
Date:   Mon, 5 Jun 2023 16:13:45 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de
Cc:     decui@...rosoft.com, rick.p.edgecombe@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
        thomas.lendacky@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCHv2 2/3] x86/tdx: Fix race between set_memory_encrypted()
 and load_unaligned_zeropad()

On 5/26/23 05:02, 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_status_change_finish() called after adjusting direct mapping
> and it converts the memory to shared.
> 
> It is okay to have a shared mapping of memory that is not converted
> properly. handle_mmio() knows how to deal with load_unaligned_zeropad()
> stepping on it.

Yeah, as other said, the changelog grammar here is a bit funky.  Can you
fix it up and resend, please?