^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) SRBDS - Special Register Buffer Data Sampling
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) =============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) SRBDS is a hardware vulnerability that allows MDS :doc:`mds` techniques to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) infer values returned from special register accesses. Special register
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) accesses are accesses to off core registers. According to Intel's evaluation,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) the special register reads that have a security expectation of privacy are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) RDRAND, RDSEED and SGX EGETKEY.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) When RDRAND, RDSEED and EGETKEY instructions are used, the data is moved
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) to the core through the special register mechanism that is susceptible
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) to MDS attacks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) Affected processors
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) -------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) Core models (desktop, mobile, Xeon-E3) that implement RDRAND and/or RDSEED may
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) be affected.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) A processor is affected by SRBDS if its Family_Model and stepping is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) in the following list, with the exception of the listed processors
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) exporting MDS_NO while Intel TSX is available yet not enabled. The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) latter class of processors are only affected when Intel TSX is enabled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) by software using TSX_CTRL_MSR otherwise they are not affected.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) ============= ============ ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) common name Family_Model Stepping
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) ============= ============ ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) IvyBridge 06_3AH All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) Haswell 06_3CH All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) Haswell_L 06_45H All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) Haswell_G 06_46H All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) Broadwell_G 06_47H All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) Broadwell 06_3DH All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) Skylake_L 06_4EH All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) Skylake 06_5EH All
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) Kabylake_L 06_8EH <= 0xC
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) Kabylake 06_9EH <= 0xD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) ============= ============ ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) Related CVEs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) ------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) The following CVE entry is related to this SRBDS issue:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) ============== ===== =====================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) CVE-2020-0543 SRBDS Special Register Buffer Data Sampling
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) ============== ===== =====================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) Attack scenarios
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) ----------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) An unprivileged user can extract values returned from RDRAND and RDSEED
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) executed on another core or sibling thread using MDS techniques.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) Mitigation mechanism
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) --------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) Intel will release microcode updates that modify the RDRAND, RDSEED, and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) EGETKEY instructions to overwrite secret special register data in the shared
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) staging buffer before the secret data can be accessed by another logical
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) processor.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) During execution of the RDRAND, RDSEED, or EGETKEY instructions, off-core
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) accesses from other logical processors will be delayed until the special
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) register read is complete and the secret data in the shared staging buffer is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) overwritten.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) This has three effects on performance:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) #. RDRAND, RDSEED, or EGETKEY instructions have higher latency.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) #. Executing RDRAND at the same time on multiple logical processors will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) serialized, resulting in an overall reduction in the maximum RDRAND
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) bandwidth.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) #. Executing RDRAND, RDSEED or EGETKEY will delay memory accesses from other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) logical processors that miss their core caches, with an impact similar to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) legacy locked cache-line-split accesses.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) The microcode updates provide an opt-out mechanism (RNGDS_MITG_DIS) to disable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) the mitigation for RDRAND and RDSEED instructions executed outside of Intel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) Software Guard Extensions (Intel SGX) enclaves. On logical processors that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) disable the mitigation using this opt-out mechanism, RDRAND and RDSEED do not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) take longer to execute and do not impact performance of sibling logical
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) processors memory accesses. The opt-out mechanism does not affect Intel SGX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) enclaves (including execution of RDRAND or RDSEED inside an enclave, as well
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) as EGETKEY execution).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) IA32_MCU_OPT_CTRL MSR Definition
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) --------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) Along with the mitigation for this issue, Intel added a new thread-scope
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) IA32_MCU_OPT_CTRL MSR, (address 0x123). The presence of this MSR and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) RNGDS_MITG_DIS (bit 0) is enumerated by CPUID.(EAX=07H,ECX=0).EDX[SRBDS_CTRL =
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) 9]==1. This MSR is introduced through the microcode update.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) Setting IA32_MCU_OPT_CTRL[0] (RNGDS_MITG_DIS) to 1 for a logical processor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) disables the mitigation for RDRAND and RDSEED executed outside of an Intel SGX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) enclave on that logical processor. Opting out of the mitigation for a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) particular logical processor does not affect the RDRAND and RDSEED mitigations
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) for other logical processors.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) Note that inside of an Intel SGX enclave, the mitigation is applied regardless
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) of the value of RNGDS_MITG_DS.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) Mitigation control on the kernel command line
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) ---------------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) The kernel command line allows control over the SRBDS mitigation at boot time
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) with the option "srbds=". The option for this is:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) ============= =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) off This option disables SRBDS mitigation for RDRAND and RDSEED on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) affected platforms.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) ============= =============================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) SRBDS System Information
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) ------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) The Linux kernel provides vulnerability status information through sysfs. For
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) SRBDS this can be accessed by the following sysfs file:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) /sys/devices/system/cpu/vulnerabilities/srbds
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) The possible values contained in this file are:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) ============================== =============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) Not affected Processor not vulnerable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) Vulnerable Processor vulnerable and mitigation disabled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) Vulnerable: No microcode Processor vulnerable and microcode is missing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) mitigation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) Mitigation: Microcode Processor is vulnerable and mitigation is in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) effect.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) Mitigation: TSX disabled Processor is only vulnerable when TSX is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) enabled while this system was booted with TSX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) disabled.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Unknown: Dependent on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) hypervisor status Running on virtual guest processor that is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) affected but with no way to know if host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) processor is mitigated or vulnerable.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) ============================== =============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) SRBDS Default mitigation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) ------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) This new microcode serializes processor access during execution of RDRAND,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) RDSEED ensures that the shared buffer is overwritten before it is released for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) reuse. Use the "srbds=off" kernel command line to disable the mitigation for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) RDRAND and RDSEED.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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