lkml.org 
[lkml]   [2018]   [Aug]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: SEV guest regression in 4.18
    From
    Date


    On 08/23/2018 11:16 AM, Paolo Bonzini wrote:
    > On 23/08/2018 17:29, Sean Christopherson wrote:
    >> On Thu, Aug 23, 2018 at 01:26:55PM +0200, Paolo Bonzini wrote:
    >>> On 22/08/2018 22:11, Brijesh Singh wrote:
    >>>>
    >>>> Yes, this is one of approach I have in mind. It will avoid splitting
    >>>> the larger pages; I am thinking that early in boot code we can lookup
    >>>> for this special section and decrypt it in-place and probably maps with
    >>>> C=0. Only downside, it will increase data section footprint a bit
    >>>> because we need to align this section to PM_SIZE.
    >>>
    >>> If you can ensure it doesn't span a PMD, maybe it does not need to be
    >>> aligned; you could establish a C=0 mapping of the whole 2M around it.
    >>
    >> Wouldn't that result in exposing/leaking whatever code/data happened
    >> to reside on the same 2M page (or corrupting it if the entire page
    >> isn't decrypted)? Or are you suggesting that we'd also leave the
    >> encrypted mapping intact?
    >
    > Yes, exactly the latter, because...


    Hardware does not enforce coherency between the encrypted and
    unencrypted mapping for the same physical page. So, creating a
    two mapping of same physical address will lead a possible data
    corruption.

    Note, SME creates two mapping of the same physical address to perform
    in-place encryption of kernel and initrd images; this is a special case
    and APM documents steps on how to do this.


    >
    >> Does hardware include the C-bit in the cache tag?
    >
    > ... the C-bit is effectively part of the physical address and hence of
    > the cache tag. The kernel is already relying on this to properly
    > encrypt/decrypt pages, if I remember correctly.
    >
    > Paolo
    >

    \
     
     \ /
      Last update: 2018-08-24 17:43    [W:2.681 / U:0.088 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site