Patch "Documentation/hw-vuln: Add documentation for RFDS" has been added to the 6.7-stable tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



This is a note to let you know that I've just added the patch titled

    Documentation/hw-vuln: Add documentation for RFDS

to the 6.7-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     documentation-hw-vuln-add-documentation-for-rfds.patch
and it can be found in the queue-6.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 168e79b5f35d934ba11d97213ff1195a65941c6d Mon Sep 17 00:00:00 2001
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Date: Mon, 11 Mar 2024 12:29:43 -0700
Subject: Documentation/hw-vuln: Add documentation for RFDS

From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>

commit 4e42765d1be01111df0c0275bbaf1db1acef346e upstream.

Add the documentation for transient execution vulnerability Register
File Data Sampling (RFDS) that affects Intel Atom CPUs.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 Documentation/admin-guide/hw-vuln/index.rst                  |    1 
 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst |  104 +++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst

--- a/Documentation/admin-guide/hw-vuln/index.rst
+++ b/Documentation/admin-guide/hw-vuln/index.rst
@@ -21,3 +21,4 @@ are configurable at compile, boot or run
    cross-thread-rsb
    srso
    gather_data_sampling
+   reg-file-data-sampling
--- /dev/null
+++ b/Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
@@ -0,0 +1,104 @@
+==================================
+Register File Data Sampling (RFDS)
+==================================
+
+Register File Data Sampling (RFDS) is a microarchitectural vulnerability that
+only affects Intel Atom parts(also branded as E-cores). RFDS may allow
+a malicious actor to infer data values previously used in floating point
+registers, vector registers, or integer registers. RFDS does not provide the
+ability to choose which data is inferred. CVE-2023-28746 is assigned to RFDS.
+
+Affected Processors
+===================
+Below is the list of affected Intel processors [#f1]_:
+
+   ===================  ============
+   Common name          Family_Model
+   ===================  ============
+   ATOM_GOLDMONT           06_5CH
+   ATOM_GOLDMONT_D         06_5FH
+   ATOM_GOLDMONT_PLUS      06_7AH
+   ATOM_TREMONT_D          06_86H
+   ATOM_TREMONT            06_96H
+   ALDERLAKE               06_97H
+   ALDERLAKE_L             06_9AH
+   ATOM_TREMONT_L          06_9CH
+   RAPTORLAKE              06_B7H
+   RAPTORLAKE_P            06_BAH
+   ATOM_GRACEMONT          06_BEH
+   RAPTORLAKE_S            06_BFH
+   ===================  ============
+
+As an exception to this table, Intel Xeon E family parts ALDERLAKE(06_97H) and
+RAPTORLAKE(06_B7H) codenamed Catlow are not affected. They are reported as
+vulnerable in Linux because they share the same family/model with an affected
+part. Unlike their affected counterparts, they do not enumerate RFDS_CLEAR or
+CPUID.HYBRID. This information could be used to distinguish between the
+affected and unaffected parts, but it is deemed not worth adding complexity as
+the reporting is fixed automatically when these parts enumerate RFDS_NO.
+
+Mitigation
+==========
+Intel released a microcode update that enables software to clear sensitive
+information using the VERW instruction. Like MDS, RFDS deploys the same
+mitigation strategy to force the CPU to clear the affected buffers before an
+attacker can extract the secrets. This is achieved by using the otherwise
+unused and obsolete VERW instruction in combination with a microcode update.
+The microcode clears the affected CPU buffers when the VERW instruction is
+executed.
+
+Mitigation points
+-----------------
+VERW is executed by the kernel before returning to user space, and by KVM
+before VMentry. None of the affected cores support SMT, so VERW is not required
+at C-state transitions.
+
+New bits in IA32_ARCH_CAPABILITIES
+----------------------------------
+Newer processors and microcode update on existing affected processors added new
+bits to IA32_ARCH_CAPABILITIES MSR. These bits can be used to enumerate
+vulnerability and mitigation capability:
+
+- Bit 27 - RFDS_NO - When set, processor is not affected by RFDS.
+- Bit 28 - RFDS_CLEAR - When set, processor is affected by RFDS, and has the
+  microcode that clears the affected buffers on VERW execution.
+
+Mitigation control on the kernel command line
+---------------------------------------------
+The kernel command line allows to control RFDS mitigation at boot time with the
+parameter "reg_file_data_sampling=". The valid arguments are:
+
+  ==========  =================================================================
+  on          If the CPU is vulnerable, enable mitigation; CPU buffer clearing
+              on exit to userspace and before entering a VM.
+  off         Disables mitigation.
+  ==========  =================================================================
+
+Mitigation default is selected by CONFIG_MITIGATION_RFDS.
+
+Mitigation status information
+-----------------------------
+The Linux kernel provides a sysfs interface to enumerate the current
+vulnerability status of the system: whether the system is vulnerable, and
+which mitigations are active. The relevant sysfs file is:
+
+	/sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
+
+The possible values in this file are:
+
+  .. list-table::
+
+     * - 'Not affected'
+       - The processor is not vulnerable
+     * - 'Vulnerable'
+       - The processor is vulnerable, but no mitigation enabled
+     * - 'Vulnerable: No microcode'
+       - The processor is vulnerable but microcode is not updated.
+     * - 'Mitigation: Clear Register File'
+       - The processor is vulnerable and the CPU buffer clearing mitigation is
+	 enabled.
+
+References
+----------
+.. [#f1] Affected Processors
+   https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html


Patches currently in stable-queue which might be from pawan.kumar.gupta@xxxxxxxxxxxxxxx are

queue-6.7/documentation-hw-vuln-add-documentation-for-rfds.patch
queue-6.7/x86-rfds-mitigate-register-file-data-sampling-rfds.patch
queue-6.7/x86-mmio-disable-kvm-mitigation-when-x86_feature_clear_cpu_buf-is-set.patch
queue-6.7/kvm-x86-export-rfds_no-and-rfds_clear-to-guests.patch




[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux