netdev - RE: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of bss

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Message-ID: <BYAPR21MB16886DA6333D33A9B2D5CBE0D7099@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Fri, 18 Nov 2022 02:59:48 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tom Lendacky <thomas.lendacky@....com>,
        "hpa@...or.com" <hpa@...or.com>, KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
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Subject: RE: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of
 bss_decrypted consistently

From: Tom Lendacky <thomas.lendacky@....com> Sent: Wednesday, November 16, 2022 1:16 PM
> 
> On 11/16/22 14:35, Tom Lendacky wrote:
> > On 11/16/22 12:41, 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_decrytped_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.
> >>
> >> Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> 
> Meant to add this in the previous reply...
> 
> With the change to use sme_me_mask directly
> 
> Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
> 

Thanks for the reviews.  And I see your point about sme_me_mask.  I had
not previously noticed that it is defined in the module, so no need to use
a getter function.

Michael