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.
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.
So check sme_me_mask in mem_encrypt_free_decrypted_mem() too.
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."
> Fixes: e9d1d2bb75b2 ("treewide: Replace the use of mem_encrypt_active() with cc_platform_has()")
So when you say Fixes - this is an issue only for vTOM-using VMs and
before yours, there were none. And yours needs more enablement than just
this patch.
So does this one really need to be backported to stable@?
I'm asking because there's AI which will pick it up based on this Fixes
tag up but that AI is still not that smart to replace us all. :-)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
