Re: [Patch v3 05/14] x86/mm: Handle decryption/re-encryption of bss_decrypted consistently

[Tom Lendacky]

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@xxxxxxxxxxxxx>

Meant to add this in the previous reply...

With the change to use sme_me_mask directly

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

> > ---
> >   arch/x86/mm/mem_encrypt_amd.c | 10 +++++++---
> >   1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
> > index 9c4d8db..5a51343 100644
> > --- a/arch/x86/mm/mem_encrypt_amd.c
> > +++ b/arch/x86/mm/mem_encrypt_amd.c
> > @@ -513,10 +513,14 @@ void __init mem_encrypt_free_decrypted_mem(void)
> >       npages = (vaddr_end - vaddr) >> PAGE_SHIFT;
> >       /*
> > -     * The unused memory range was mapped decrypted, change the encryption
> > -     * attribute from decrypted to encrypted before freeing it.
> > +     * If the unused memory range was mapped decrypted, change the 
> > encryption
> > +     * attribute from decrypted to encrypted before freeing it. Base the
> > +     * re-encryption on the same condition used for the decryption in
> > +     * sme_postprocess_startup(). Higher level abstractions, such as
> > +     * CC_ATTR_MEM_ENCRYPT, aren't necessarily equivalent in a Hyper-V VM
> > +     * using vTOM, where sme_me_mask is always zero.
> >        */
> > -    if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
> > +    if (sme_get_me_mask()) {
>
> To be consistent within this file, you should use sme_me_mask directly.
>
> Thanks,
> Tom
>
> >           r = set_memory_encrypted(vaddr, npages);
> >           if (r) {
> >               pr_warn("failed to free unused decrypted pages\n");