linux-efi.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ard Biesheuvel <ardb@kernel.org>
To: Andrew Scull <ascull@google.com>
Cc: Dov Murik <dovmurik@linux.ibm.com>,
	linux-efi <linux-efi@vger.kernel.org>,
	Borislav Petkov <bp@suse.de>, Ashish Kalra <ashish.kalra@amd.com>,
	Brijesh Singh <brijesh.singh@amd.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	James Morris <jmorris@namei.org>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Andi Kleen <ak@linux.intel.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	James Bottomley <jejb@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@linux.ibm.com>,
	Jim Cadden <jcadden@ibm.com>,
	linux-coco@lists.linux.dev,
	linux-security-module@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] virt: Add sev_secret module to expose confidential computing secrets
Date: Mon, 16 Aug 2021 11:56:56 +0200	[thread overview]
Message-ID: <CAMj1kXFC-cizTw2Tv40uZHdLArKtdMNxdQXWoPWSL-8qexdkLQ@mail.gmail.com> (raw)
In-Reply-To: <YRZuIIVIzMfgjtEl@google.com>

On Fri, 13 Aug 2021 at 15:05, Andrew Scull <ascull@google.com> wrote:
>
> On Mon, Aug 09, 2021 at 07:01:57PM +0000, Dov Murik wrote:
> > The new sev_secret module exposes the confidential computing (coco)
> > secret area via securityfs interface.
> >
> > When the module is loaded (and securityfs is mounted, typically under
> > /sys/kernel/security), a "coco/sev_secret" directory is created in
> > securityfs.  In it, a file is created for each secret entry.  The name
> > of each such file is the GUID of the secret entry, and its content is
> > the secret data.
> >
> > This allows applications running in a confidential computing setting to
> > read secrets provided by the guest owner via a secure secret injection
> > mechanism (such as AMD SEV's LAUNCH_SECRET command).
> >
> > Removing (unlinking) files in the "coco/sev_secret" directory will zero
> > out the secret in memory, and remove the filesystem entry.  If the
> > module is removed and loaded again, that secret will not appear in the
> > filesystem.
>
> We've also been looking into a similar secret mechanism recently in the
> context of Android and protected KVM [1]. Our secrets would come from a
> different source, likely described as a reserved-memory node in the DT,
> but would need to be exposed to userspace in the same way as the SEV
> secrets. Originally I tried using a character device, but this approach
> with securityfs feels neater to me.
>

Agreed. I particularly like how deleting the file wipes the secret from memory.

> We're also looking to pass secrets from the bootloader to Linux, outside
> of any virtualization or confidential compute context (at least a far as
> I have understood the meaning of the term). Again, this feels like it
> would be exposed to userspace in the same way.
>

Indeed.

> It would be good to be able to share the parts that would be common. I
> expect that would mean the operations for a secret file and for a
> directory of secrets at a minimum. But it might also influence the paths
> in securityfs; I see, looking back, that the "coco" directory was added
> since the RFC but would a generalized "secret" subsystem make sense? Or
> would it be preferable for each case to define their own path?
>

I think we should avoid 'secret', to be honest. Even if protected KVM
is not riding the SEV/TDX wave, I think confidential computing is
still an accurate description of its semantics.

> [1] -- https://lwn.net/Articles/836693/
>
> > +static int sev_secret_unlink(struct inode *dir, struct dentry *dentry)
> > +{
> > +     struct sev_secret *s = sev_secret_get();
> > +     struct inode *inode = d_inode(dentry);
> > +     struct secret_entry *e = (struct secret_entry *)inode->i_private;
> > +     int i;
> > +
> > +     if (e) {
> > +             /* Zero out the secret data */
> > +             memzero_explicit(e->data, secret_entry_data_len(e));
>
> Would there be a benefit in flushing these zeros?
>

Do you mean cache clean+invalidate? Better to be precise here.


> > +             e->guid = NULL_GUID;
> > +     }
> > +
> > +     inode->i_private = NULL;
> > +
> > +     for (i = 0; i < SEV_SECRET_NUM_FILES; i++)
> > +             if (s->fs_files[i] == dentry)
> > +                     s->fs_files[i] = NULL;
> > +
> > +     /*
> > +      * securityfs_remove tries to lock the directory's inode, but we reach
> > +      * the unlink callback when it's already locked
> > +      */
> > +     inode_unlock(dir);
> > +     securityfs_remove(dentry);
> > +     inode_lock(dir);
> > +
> > +     return 0;
> > +}

  reply	other threads:[~2021-08-16  9:57 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-09 19:01 [PATCH 0/3] Allow access to confidential computing secret area in SEV guests Dov Murik
2021-08-09 19:01 ` [PATCH 1/3] efi/libstub: Copy confidential computing secret area Dov Murik
2021-08-09 19:01 ` [PATCH 2/3] efi: Reserve " Dov Murik
2021-08-09 19:01 ` [PATCH 3/3] virt: Add sev_secret module to expose confidential computing secrets Dov Murik
2021-08-13 13:05   ` Andrew Scull
2021-08-16  9:56     ` Ard Biesheuvel [this message]
2021-08-19 13:02       ` Andrew Scull
2021-08-20 18:36         ` Dov Murik
2021-08-23 19:21           ` Andrew Scull
2021-09-02 12:59   ` Greg KH
2021-09-02 18:14     ` Dov Murik
2021-09-02 12:57 ` [PATCH 0/3] Allow access to confidential computing secret area in SEV guests Greg KH
2021-09-02 14:35   ` James Bottomley
2021-09-02 15:05     ` Greg KH
2021-09-02 15:19       ` James Bottomley
2021-09-02 16:09         ` Greg KH
2021-09-02 16:19           ` James Bottomley
2021-09-02 16:31             ` Greg KH

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAMj1kXFC-cizTw2Tv40uZHdLArKtdMNxdQXWoPWSL-8qexdkLQ@mail.gmail.com \
    --to=ardb@kernel.org \
    --cc=ak@linux.intel.com \
    --cc=ascull@google.com \
    --cc=ashish.kalra@amd.com \
    --cc=bp@suse.de \
    --cc=brijesh.singh@amd.com \
    --cc=dgilbert@redhat.com \
    --cc=dovmurik@linux.ibm.com \
    --cc=jcadden@ibm.com \
    --cc=jejb@linux.ibm.com \
    --cc=jmorris@namei.org \
    --cc=linux-coco@lists.linux.dev \
    --cc=linux-efi@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-security-module@vger.kernel.org \
    --cc=serge@hallyn.com \
    --cc=thomas.lendacky@amd.com \
    --cc=tobin@linux.ibm.com \
    --subject='Re: [PATCH 3/3] virt: Add sev_secret module to expose confidential computing secrets' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).