linux-kernel - Re: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of bss

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Message-ID: <Y4SShb6nMz3gqkwh@zn.tnic>
Date:   Mon, 28 Nov 2022 11:50:45 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Sathyanarayanan Kuppuswamy 
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Subject: Re: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of
 bss_decrypted consistently

On Tue, Nov 22, 2022 at 05:59:04PM +0000, Michael Kelley (LINUX) wrote:
> Right.  But here's my point:  With current code and an image built with
> CONFIG_AMD_MEM_ENCRYPT=y and running as a TDX guest,
> sme_postprocess_startup() will not decrypt the bss_decrypted section.
> Then later mem_encrypt_free_decrypted_mem() will run, see that
> CC_ATTR_MEM_ENCRYPT is true, and try to re-encrypt the memory.
> In other words, a TDX guest would break in the same way as a Hyper-V
> vTOM guest would break.  This patch fixes the problem for both cases.

I guess making the check more concrete by checking sme_me_mask directly
along with a comment makes sense.

We need to be very careful here not to fragment the code too much for
all the different guest types.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette