Re: [Patch v4 04/13] x86/mm: Handle decryption/re-encryption of bss_decrypted consistently

[Bjorn Helgaas]

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)