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;
> > +}
next prev parent 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
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