summaryrefslogtreecommitdiffstats
path: root/Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst')
-rw-r--r--Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst150
1 files changed, 150 insertions, 0 deletions
diff --git a/Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst b/Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst
new file mode 100644
index 000000000..966c9b329
--- /dev/null
+++ b/Documentation/admin-guide/hw-vuln/special-register-buffer-data-sampling.rst
@@ -0,0 +1,150 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+SRBDS - Special Register Buffer Data Sampling
+=============================================
+
+SRBDS is a hardware vulnerability that allows MDS
+Documentation/admin-guide/hw-vuln/mds.rst techniques to
+infer values returned from special register accesses. Special register
+accesses are accesses to off core registers. According to Intel's evaluation,
+the special register reads that have a security expectation of privacy are
+RDRAND, RDSEED and SGX EGETKEY.
+
+When RDRAND, RDSEED and EGETKEY instructions are used, the data is moved
+to the core through the special register mechanism that is susceptible
+to MDS attacks.
+
+Affected processors
+-------------------
+Core models (desktop, mobile, Xeon-E3) that implement RDRAND and/or RDSEED may
+be affected.
+
+A processor is affected by SRBDS if its Family_Model and stepping is
+in the following list, with the exception of the listed processors
+exporting MDS_NO while Intel TSX is available yet not enabled. The
+latter class of processors are only affected when Intel TSX is enabled
+by software using TSX_CTRL_MSR otherwise they are not affected.
+
+ ============= ============ ========
+ common name Family_Model Stepping
+ ============= ============ ========
+ IvyBridge 06_3AH All
+
+ Haswell 06_3CH All
+ Haswell_L 06_45H All
+ Haswell_G 06_46H All
+
+ Broadwell_G 06_47H All
+ Broadwell 06_3DH All
+
+ Skylake_L 06_4EH All
+ Skylake 06_5EH All
+
+ Kabylake_L 06_8EH <= 0xC
+ Kabylake 06_9EH <= 0xD
+ ============= ============ ========
+
+Related CVEs
+------------
+
+The following CVE entry is related to this SRBDS issue:
+
+ ============== ===== =====================================
+ CVE-2020-0543 SRBDS Special Register Buffer Data Sampling
+ ============== ===== =====================================
+
+Attack scenarios
+----------------
+An unprivileged user can extract values returned from RDRAND and RDSEED
+executed on another core or sibling thread using MDS techniques.
+
+
+Mitigation mechanism
+--------------------
+Intel will release microcode updates that modify the RDRAND, RDSEED, and
+EGETKEY instructions to overwrite secret special register data in the shared
+staging buffer before the secret data can be accessed by another logical
+processor.
+
+During execution of the RDRAND, RDSEED, or EGETKEY instructions, off-core
+accesses from other logical processors will be delayed until the special
+register read is complete and the secret data in the shared staging buffer is
+overwritten.
+
+This has three effects on performance:
+
+#. RDRAND, RDSEED, or EGETKEY instructions have higher latency.
+
+#. Executing RDRAND at the same time on multiple logical processors will be
+ serialized, resulting in an overall reduction in the maximum RDRAND
+ bandwidth.
+
+#. Executing RDRAND, RDSEED or EGETKEY will delay memory accesses from other
+ logical processors that miss their core caches, with an impact similar to
+ legacy locked cache-line-split accesses.
+
+The microcode updates provide an opt-out mechanism (RNGDS_MITG_DIS) to disable
+the mitigation for RDRAND and RDSEED instructions executed outside of Intel
+Software Guard Extensions (Intel SGX) enclaves. On logical processors that
+disable the mitigation using this opt-out mechanism, RDRAND and RDSEED do not
+take longer to execute and do not impact performance of sibling logical
+processors memory accesses. The opt-out mechanism does not affect Intel SGX
+enclaves (including execution of RDRAND or RDSEED inside an enclave, as well
+as EGETKEY execution).
+
+IA32_MCU_OPT_CTRL MSR Definition
+--------------------------------
+Along with the mitigation for this issue, Intel added a new thread-scope
+IA32_MCU_OPT_CTRL MSR, (address 0x123). The presence of this MSR and
+RNGDS_MITG_DIS (bit 0) is enumerated by CPUID.(EAX=07H,ECX=0).EDX[SRBDS_CTRL =
+9]==1. This MSR is introduced through the microcode update.
+
+Setting IA32_MCU_OPT_CTRL[0] (RNGDS_MITG_DIS) to 1 for a logical processor
+disables the mitigation for RDRAND and RDSEED executed outside of an Intel SGX
+enclave on that logical processor. Opting out of the mitigation for a
+particular logical processor does not affect the RDRAND and RDSEED mitigations
+for other logical processors.
+
+Note that inside of an Intel SGX enclave, the mitigation is applied regardless
+of the value of RNGDS_MITG_DS.
+
+Mitigation control on the kernel command line
+---------------------------------------------
+The kernel command line allows control over the SRBDS mitigation at boot time
+with the option "srbds=". The option for this is:
+
+ ============= =============================================================
+ off This option disables SRBDS mitigation for RDRAND and RDSEED on
+ affected platforms.
+ ============= =============================================================
+
+SRBDS System Information
+------------------------
+The Linux kernel provides vulnerability status information through sysfs. For
+SRBDS this can be accessed by the following sysfs file:
+/sys/devices/system/cpu/vulnerabilities/srbds
+
+The possible values contained in this file are:
+
+ ============================== =============================================
+ Not affected Processor not vulnerable
+ Vulnerable Processor vulnerable and mitigation disabled
+ Vulnerable: No microcode Processor vulnerable and microcode is missing
+ mitigation
+ Mitigation: Microcode Processor is vulnerable and mitigation is in
+ effect.
+ Mitigation: TSX disabled Processor is only vulnerable when TSX is
+ enabled while this system was booted with TSX
+ disabled.
+ Unknown: Dependent on
+ hypervisor status Running on virtual guest processor that is
+ affected but with no way to know if host
+ processor is mitigated or vulnerable.
+ ============================== =============================================
+
+SRBDS Default mitigation
+------------------------
+This new microcode serializes processor access during execution of RDRAND,
+RDSEED ensures that the shared buffer is overwritten before it is released for
+reuse. Use the "srbds=off" kernel command line to disable the mitigation for
+RDRAND and RDSEED.