summaryrefslogtreecommitdiffstats
path: root/Documentation/ABI/testing/evm
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2026-08-19 10:09:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2026-08-19 10:09:22 -0700
commitf4cdf7ca9a1fdcca413157df19753f388a5a224e (patch)
tree60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/ABI/testing/evm
downloadlinux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz
linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab: - v4l2-core: added ISP statistics support and per-block validation - v4l2-core: Allow unknown HDR10 white point and luminance - New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor - New codec: Milos: VPU v2.0 codec support - isp driver: gained support for Dreamchip RPPX1 ISP framework - vsp1 driver: gained support for RZ/T2H and RZ/N2H - Novalake driver: gained CVS support for new NVL hardware - dvb-core: fix feed leak on failed DMX_ADD_PID - several driver fixes, cleanups and minor improvements * tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits) media: ipu-bridge: check all DMI entries when overriding sensor rotation media: v4l2-async: avoid deleting unlinked ASC entry on link error media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement media: intel/ipu6: fix async notifier cleanup leak on parse error media: staging/ipu7: fix async notifier UAF on probe error path media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem() media: rcar-isp: Fix VSPX reference leaks media: rcar-isp: Release ISPCORE resources media: i2c: imx415: Release runtime PM reference on VBLANK error media: i2c: imx415: Return test pattern write errors media: renesas: vsp1: Declare index variables in for loop statement media: renesas: vsp1: Make reset control optional to support platforms without a reset line media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs media: nxp: imx8-isi: Add additional 32-bit RGB format support media: nxp: imx8-isi: Add 16-bit raw Bayer format support media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks media: nxp: imx8-isi: Correct color map between V4L2 and ISI ...
Diffstat (limited to 'Documentation/ABI/testing/evm')
-rw-r--r--Documentation/ABI/testing/evm109
1 files changed, 109 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/evm b/Documentation/ABI/testing/evm
new file mode 100644
index 000000000..db3007bab
--- /dev/null
+++ b/Documentation/ABI/testing/evm
@@ -0,0 +1,109 @@
+What: /sys/kernel/security/evm
+What: /sys/kernel/security/*/evm
+Date: March 2011
+Contact: Mimi Zohar <zohar@us.ibm.com>
+Description:
+ EVM protects a file's security extended attributes(xattrs)
+ against integrity attacks. The initial method maintains an
+ HMAC-sha1 value across the extended attributes, storing the
+ value as the extended attribute 'security.evm'.
+
+ EVM supports two classes of security.evm. The first is
+ an HMAC-sha1 generated locally with a
+ trusted/encrypted key stored in the Kernel Key
+ Retention System. The second is a digital signature
+ generated either locally or remotely using an
+ asymmetric key. These keys are loaded onto root's
+ keyring using keyctl, and EVM is then enabled by
+ echoing a value to <securityfs>/evm made up of the
+ following bits:
+
+ === ==================================================
+ Bit Effect
+ === ==================================================
+ 0 Enable HMAC validation and creation
+ 1 Enable digital signature validation
+ 2 Permit modification of EVM-protected metadata at
+ runtime. Not supported if HMAC validation and
+ creation is enabled (deprecated).
+ 3 Require asymmetric signatures to be version 3
+ 31 Disable further runtime modification of EVM policy
+ === ==================================================
+
+ For example::
+
+ echo 1 ><securityfs>/evm
+
+ will enable HMAC validation and creation
+
+ ::
+
+ echo 0x80000003 ><securityfs>/evm
+
+ will enable HMAC and digital signature validation and
+ HMAC creation and disable all further modification of policy.
+
+ ::
+
+ echo 0x80000006 ><securityfs>/evm
+
+ will enable digital signature validation, permit
+ modification of EVM-protected metadata and
+ disable all further modification of policy. This option is now
+ deprecated in favor of::
+
+ echo 0x80000002 ><securityfs>/evm
+
+ as the outstanding issues that prevent the usage of EVM portable
+ signatures have been solved.
+
+ Echoing a value is additive, the new value is added to the
+ existing initialization flags.
+
+ For example, after::
+
+ echo 2 ><securityfs>/evm
+
+ another echo can be performed::
+
+ echo 1 ><securityfs>/evm
+
+ and the resulting value will be 3.
+
+ Note that once an HMAC key has been loaded, it will no longer
+ be possible to enable metadata modification. Signaling that an
+ HMAC key has been loaded will clear the corresponding flag.
+ For example, if the current value is 6 (2 and 4 set)::
+
+ echo 1 ><securityfs>/evm
+
+ will set the new value to 3 (4 cleared).
+
+ Loading an HMAC key is the only way to disable metadata
+ modification.
+
+ Until key loading has been signaled EVM can not create
+ or validate the 'security.evm' xattr, but returns
+ INTEGRITY_UNKNOWN. Loading keys and signaling EVM
+ should be done as early as possible. Normally this is
+ done in the initramfs, which has already been measured
+ as part of the trusted boot. For more information on
+ creating and loading existing trusted/encrypted keys,
+ refer to:
+ Documentation/security/keys/trusted-encrypted.rst. Both
+ dracut (via 97masterkey and 98integrity) and systemd (via
+ core/ima-setup) have support for loading keys at boot
+ time.
+
+What: /sys/kernel/security/*/evm/evm_xattrs
+Date: April 2018
+Contact: Matthew Garrett <mjg59@google.com>
+Description:
+ Shows the set of extended attributes used to calculate or
+ validate the EVM signature, and allows additional attributes
+ to be added at runtime. Any signatures generated after
+ additional attributes are added (and on files possessing those
+ additional attributes) will only be valid if the same
+ additional attributes are configured on system boot. Writing
+ a single period (.) will lock the xattr list from any further
+ modification.