linux-kernel - Re: [Patch v4 04/13] x86/mm: Handle decryption/re-encryption of bss

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Message-ID: <20221229165431.GA611286@bhelgaas>
Date:   Thu, 29 Dec 2022 10:54:31 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Michael Kelley <mikelley@...rosoft.com>, hpa@...or.com,
        kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, luto@...nel.org, peterz@...radead.org,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, lpieralisi@...nel.org, robh@...nel.org,
        kw@...ux.com, bhelgaas@...gle.com, arnd@...db.de,
        hch@...radead.org, m.szyprowski@...sung.com, robin.murphy@....com,
        thomas.lendacky@....com, brijesh.singh@....com, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com,
        Tianyu.Lan@...rosoft.com, kirill.shutemov@...ux.intel.com,
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        x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
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        iommu@...ts.linux.dev
Subject: Re: [Patch v4 04/13] x86/mm: Handle decryption/re-encryption of
 bss_decrypted consistently

On Thu, Dec 29, 2022 at 01:17:48PM +0100, Borislav Petkov wrote:
> On Thu, Dec 01, 2022 at 07:30:22PM -0800, Michael Kelley wrote:
> > Current code in sme_postprocess_startup() decrypts the bss_decrypted
> > section when sme_me_mask is non-zero.  But code in
> > mem_encrypt_free_decrypted_mem() re-encrypts the unused portion based
> > on CC_ATTR_MEM_ENCRYPT.  In a Hyper-V guest VM using vTOM, these
> > conditions are not equivalent as sme_me_mask is always zero when
> > using vTOM.  Consequently, mem_encrypt_free_decrypted_mem() attempts
> > to re-encrypt memory that was never decrypted.
> > 
> > Fix this in mem_encrypt_free_decrypted_mem() by conditioning the
> > re-encryption on the same test for non-zero sme_me_mask.  Hyper-V
> > guests using vTOM don't need the bss_decrypted section to be
> > decrypted, so skipping the decryption/re-encryption doesn't cause
> > a problem.
> 
> Lemme simplify the formulations a bit:
> 
> "sme_postprocess_startup() decrypts the bss_decrypted ection when me_mask
> sme_is non-zero.

s/ection/section/

(In case you copy/paste this text without noticing the typo)