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Message-ID: <YZZKXowcApyC/CEF@kroah.com>
Date: Thu, 18 Nov 2021 13:43:10 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Dov Murik <dovmurik@...ux.ibm.com>
Cc: linux-efi@...r.kernel.org, Borislav Petkov <bp@...e.de>,
Ashish Kalra <ashish.kalra@....com>,
Brijesh Singh <brijesh.singh@....com>,
Tom Lendacky <thomas.lendacky@....com>,
Ard Biesheuvel <ardb@...nel.org>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
Andi Kleen <ak@...ux.intel.com>,
Andrew Scull <ascull@...gle.com>,
Dave Hansen <dave.hansen@...el.com>,
"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
James Bottomley <jejb@...ux.ibm.com>,
Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
Jim Cadden <jcadden@....com>,
Daniele Buono <dbuono@...ux.vnet.ibm.com>,
linux-coco@...ts.linux.dev, linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/4] virt: Add efi_secret module to expose
confidential computing secrets
On Thu, Nov 18, 2021 at 11:33:58AM +0000, Dov Murik wrote:
> The new efi_secret module exposes the confidential computing (coco)
> EFI secret area via securityfs interface.
>
> When the module is loaded (and securityfs is mounted, typically under
> /sys/kernel/security), a "coco/efi_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/efi_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.
>
> Signed-off-by: Dov Murik <dovmurik@...ux.ibm.com>
> ---
> .../ABI/testing/securityfs-coco-efi_secret | 50 +++
> drivers/virt/Kconfig | 3 +
> drivers/virt/Makefile | 1 +
> drivers/virt/coco/efi_secret/Kconfig | 11 +
> drivers/virt/coco/efi_secret/Makefile | 2 +
> drivers/virt/coco/efi_secret/efi_secret.c | 341 ++++++++++++++++++
> 6 files changed, 408 insertions(+)
> create mode 100644 Documentation/ABI/testing/securityfs-coco-efi_secret
> create mode 100644 drivers/virt/coco/efi_secret/Kconfig
> create mode 100644 drivers/virt/coco/efi_secret/Makefile
> create mode 100644 drivers/virt/coco/efi_secret/efi_secret.c
>
> diff --git a/Documentation/ABI/testing/securityfs-coco-efi_secret b/Documentation/ABI/testing/securityfs-coco-efi_secret
> new file mode 100644
> index 000000000000..ae56976db1bc
> --- /dev/null
> +++ b/Documentation/ABI/testing/securityfs-coco-efi_secret
> @@ -0,0 +1,50 @@
> +What: security/coco/efi_secret
> +Date: October 2021
> +Contact: Dov Murik <dovmurik@...ux.ibm.com>
> +Description:
> + Exposes confidential computing (coco) EFI secrets to
> + userspace via securityfs.
> +
> + EFI can declare memory area used by confidential computing
> + platforms (such as AMD SEV and SEV-ES) for secret injection by
> + the Guest Owner during VM's launch. The secrets are encrypted
> + by the Guest Owner and decrypted inside the trusted enclave,
> + and therefore are not readable by the untrusted host.
> +
> + The efi_secret module exposes the secrets to userspace. Each
> + secret appears as a file under <securityfs>/coco/efi_secret,
> + where the filename is the GUID of the entry in the secrets
> + table.
> +
> + Two operations are supported for the files: read and unlink.
> + Reading the file returns the content of secret entry.
> + Unlinking the file overwrites the secret data with zeroes and
> + removes the entry from the filesystem. A secret cannot be read
> + after it has been unlinked.
> +
> + For example, listing the available secrets::
> +
> + # modprobe efi_secret
> + # ls -l /sys/kernel/security/coco/efi_secret
> + -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
> + -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
> + -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
> + -r--r----- 1 root root 0 Jun 28 11:54 e6f5a162-d67f-4750-a67c-5d065f2a9910
> +
> + Reading the secret data by reading a file::
> +
> + # cat /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
> + the-content-of-the-secret-data
> +
> + Wiping a secret by unlinking a file::
> +
> + # rm /sys/kernel/security/coco/efi_secret/e6f5a162-d67f-4750-a67c-5d065f2a9910
> + # ls -l /sys/kernel/security/coco/efi_secret
> + -r--r----- 1 root root 0 Jun 28 11:54 736870e5-84f0-4973-92ec-06879ce3da0b
> + -r--r----- 1 root root 0 Jun 28 11:54 83c83f7f-1356-4975-8b7e-d3a0b54312c6
> + -r--r----- 1 root root 0 Jun 28 11:54 9553f55d-3da2-43ee-ab5d-ff17f78864d2
> +
> + Note: The binary format of the secrets table injected by the
> + Guest Owner is described in
> + drivers/virt/coco/efi_secret/efi_secret.c under "Structure of
> + the EFI secret area".
> diff --git a/drivers/virt/Kconfig b/drivers/virt/Kconfig
> index 8061e8ef449f..fe7a6579b974 100644
> --- a/drivers/virt/Kconfig
> +++ b/drivers/virt/Kconfig
> @@ -36,4 +36,7 @@ source "drivers/virt/vboxguest/Kconfig"
> source "drivers/virt/nitro_enclaves/Kconfig"
>
> source "drivers/virt/acrn/Kconfig"
> +
> +source "drivers/virt/coco/efi_secret/Kconfig"
> +
> endif
> diff --git a/drivers/virt/Makefile b/drivers/virt/Makefile
> index 3e272ea60cd9..efdb015783f9 100644
> --- a/drivers/virt/Makefile
> +++ b/drivers/virt/Makefile
> @@ -8,3 +8,4 @@ obj-y += vboxguest/
>
> obj-$(CONFIG_NITRO_ENCLAVES) += nitro_enclaves/
> obj-$(CONFIG_ACRN_HSM) += acrn/
> +obj-$(CONFIG_EFI_SECRET) += coco/efi_secret/
> diff --git a/drivers/virt/coco/efi_secret/Kconfig b/drivers/virt/coco/efi_secret/Kconfig
> new file mode 100644
> index 000000000000..a39a5a90a1e5
> --- /dev/null
> +++ b/drivers/virt/coco/efi_secret/Kconfig
> @@ -0,0 +1,11 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +config EFI_SECRET
> + tristate "EFI secret area securityfs support"
> + depends on EFI
> + select EFI_COCO_SECRET
> + select SECURITYFS
> + help
> + This is a driver for accessing the EFI secret area via securityfs.
> +
> + To compile this driver as a module, choose M here.
> + The module will be called efi_secret.
Shouldn't this module auto-load only if the efi secret area is present?
What is going to cause the module to be loaded by a distro if it does
not have some sort of way to tell userspace what resources it belongs
to? Can you trigger off of a DMI or EFI attribute somehow for this?
Otherwise you are going to force distros to modify their init scripts
for this functionality, how is that going to happen?
thanks,
greg k-h
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