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* Mitigate RFDS vulnerability
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This commit is contained in:
Linus Torvalds
commit
0e33cf955f
@ -516,6 +516,7 @@ What: /sys/devices/system/cpu/vulnerabilities
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/sys/devices/system/cpu/vulnerabilities/mds
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/sys/devices/system/cpu/vulnerabilities/meltdown
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/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
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/sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
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/sys/devices/system/cpu/vulnerabilities/retbleed
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/sys/devices/system/cpu/vulnerabilities/spec_store_bypass
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/sys/devices/system/cpu/vulnerabilities/spectre_v1
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@ -21,3 +21,4 @@ are configurable at compile, boot or run time.
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cross-thread-rsb
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srso
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gather_data_sampling
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reg-file-data-sampling
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104
Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
Normal file
104
Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
Normal file
@ -0,0 +1,104 @@
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==================================
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Register File Data Sampling (RFDS)
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==================================
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Register File Data Sampling (RFDS) is a microarchitectural vulnerability that
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only affects Intel Atom parts(also branded as E-cores). RFDS may allow
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a malicious actor to infer data values previously used in floating point
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registers, vector registers, or integer registers. RFDS does not provide the
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ability to choose which data is inferred. CVE-2023-28746 is assigned to RFDS.
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Affected Processors
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===================
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Below is the list of affected Intel processors [#f1]_:
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=================== ============
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Common name Family_Model
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=================== ============
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ATOM_GOLDMONT 06_5CH
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ATOM_GOLDMONT_D 06_5FH
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ATOM_GOLDMONT_PLUS 06_7AH
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ATOM_TREMONT_D 06_86H
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ATOM_TREMONT 06_96H
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ALDERLAKE 06_97H
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ALDERLAKE_L 06_9AH
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ATOM_TREMONT_L 06_9CH
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RAPTORLAKE 06_B7H
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RAPTORLAKE_P 06_BAH
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ATOM_GRACEMONT 06_BEH
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RAPTORLAKE_S 06_BFH
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=================== ============
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As an exception to this table, Intel Xeon E family parts ALDERLAKE(06_97H) and
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RAPTORLAKE(06_B7H) codenamed Catlow are not affected. They are reported as
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vulnerable in Linux because they share the same family/model with an affected
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part. Unlike their affected counterparts, they do not enumerate RFDS_CLEAR or
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CPUID.HYBRID. This information could be used to distinguish between the
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affected and unaffected parts, but it is deemed not worth adding complexity as
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the reporting is fixed automatically when these parts enumerate RFDS_NO.
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Mitigation
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==========
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Intel released a microcode update that enables software to clear sensitive
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information using the VERW instruction. Like MDS, RFDS deploys the same
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mitigation strategy to force the CPU to clear the affected buffers before an
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attacker can extract the secrets. This is achieved by using the otherwise
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unused and obsolete VERW instruction in combination with a microcode update.
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The microcode clears the affected CPU buffers when the VERW instruction is
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executed.
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Mitigation points
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-----------------
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VERW is executed by the kernel before returning to user space, and by KVM
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before VMentry. None of the affected cores support SMT, so VERW is not required
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at C-state transitions.
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New bits in IA32_ARCH_CAPABILITIES
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----------------------------------
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Newer processors and microcode update on existing affected processors added new
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bits to IA32_ARCH_CAPABILITIES MSR. These bits can be used to enumerate
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vulnerability and mitigation capability:
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- Bit 27 - RFDS_NO - When set, processor is not affected by RFDS.
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- Bit 28 - RFDS_CLEAR - When set, processor is affected by RFDS, and has the
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microcode that clears the affected buffers on VERW execution.
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Mitigation control on the kernel command line
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---------------------------------------------
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The kernel command line allows to control RFDS mitigation at boot time with the
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parameter "reg_file_data_sampling=". The valid arguments are:
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========== =================================================================
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on If the CPU is vulnerable, enable mitigation; CPU buffer clearing
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on exit to userspace and before entering a VM.
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off Disables mitigation.
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========== =================================================================
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Mitigation default is selected by CONFIG_MITIGATION_RFDS.
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Mitigation status information
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-----------------------------
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The Linux kernel provides a sysfs interface to enumerate the current
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vulnerability status of the system: whether the system is vulnerable, and
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which mitigations are active. The relevant sysfs file is:
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/sys/devices/system/cpu/vulnerabilities/reg_file_data_sampling
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The possible values in this file are:
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.. list-table::
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* - 'Not affected'
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- The processor is not vulnerable
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* - 'Vulnerable'
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- The processor is vulnerable, but no mitigation enabled
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* - 'Vulnerable: No microcode'
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- The processor is vulnerable but microcode is not updated.
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* - 'Mitigation: Clear Register File'
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- The processor is vulnerable and the CPU buffer clearing mitigation is
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enabled.
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References
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----------
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.. [#f1] Affected Processors
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https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html
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@ -1136,6 +1136,26 @@
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The filter can be disabled or changed to another
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driver later using sysfs.
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reg_file_data_sampling=
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[X86] Controls mitigation for Register File Data
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Sampling (RFDS) vulnerability. RFDS is a CPU
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vulnerability which may allow userspace to infer
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kernel data values previously stored in floating point
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registers, vector registers, or integer registers.
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RFDS only affects Intel Atom processors.
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on: Turns ON the mitigation.
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off: Turns OFF the mitigation.
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This parameter overrides the compile time default set
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by CONFIG_MITIGATION_RFDS. Mitigation cannot be
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disabled when other VERW based mitigations (like MDS)
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are enabled. In order to disable RFDS mitigation all
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VERW based mitigations need to be disabled.
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For details see:
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Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst
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driver_async_probe= [KNL]
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List of driver names to be probed asynchronously. *
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matches with all driver names. If * is specified, the
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@ -3394,6 +3414,7 @@
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nospectre_bhb [ARM64]
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nospectre_v1 [X86,PPC]
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nospectre_v2 [X86,PPC,S390,ARM64]
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reg_file_data_sampling=off [X86]
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retbleed=off [X86]
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spec_rstack_overflow=off [X86]
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spec_store_bypass_disable=off [X86,PPC]
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@ -2623,6 +2623,17 @@ config MITIGATION_GDS_FORCE
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If in doubt, say N.
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config MITIGATION_RFDS
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bool "RFDS Mitigation"
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depends on CPU_SUP_INTEL
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default y
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help
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Enable mitigation for Register File Data Sampling (RFDS) by default.
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RFDS is a hardware vulnerability which affects Intel Atom CPUs. It
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allows unprivileged speculative access to stale data previously
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stored in floating point, vector and integer registers.
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See also <file:Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst>
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endif
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config ARCH_HAS_ADD_PAGES
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@ -506,4 +506,5 @@
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/* BUG word 2 */
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#define X86_BUG_SRSO X86_BUG(1*32 + 0) /* AMD SRSO bug */
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#define X86_BUG_DIV0 X86_BUG(1*32 + 1) /* AMD DIV0 speculation bug */
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#define X86_BUG_RFDS X86_BUG(1*32 + 2) /* CPU is vulnerable to Register File Data Sampling */
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#endif /* _ASM_X86_CPUFEATURES_H */
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@ -176,6 +176,14 @@
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* CPU is not vulnerable to Gather
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* Data Sampling (GDS).
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*/
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#define ARCH_CAP_RFDS_NO BIT(27) /*
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* Not susceptible to Register
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* File Data Sampling.
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*/
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#define ARCH_CAP_RFDS_CLEAR BIT(28) /*
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* VERW clears CPU Register
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* File.
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*/
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#define ARCH_CAP_XAPIC_DISABLE BIT(21) /*
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* IA32_XAPIC_DISABLE_STATUS MSR
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@ -422,6 +422,13 @@ static void __init mmio_select_mitigation(void)
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if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
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boot_cpu_has(X86_FEATURE_RTM)))
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setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
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/*
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* X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
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* mitigations, disable KVM-only mitigation in that case.
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*/
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if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
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static_branch_disable(&mmio_stale_data_clear);
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else
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static_branch_enable(&mmio_stale_data_clear);
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@ -473,6 +480,57 @@ static int __init mmio_stale_data_parse_cmdline(char *str)
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}
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early_param("mmio_stale_data", mmio_stale_data_parse_cmdline);
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#undef pr_fmt
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#define pr_fmt(fmt) "Register File Data Sampling: " fmt
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enum rfds_mitigations {
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RFDS_MITIGATION_OFF,
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RFDS_MITIGATION_VERW,
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RFDS_MITIGATION_UCODE_NEEDED,
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};
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/* Default mitigation for Register File Data Sampling */
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static enum rfds_mitigations rfds_mitigation __ro_after_init =
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IS_ENABLED(CONFIG_MITIGATION_RFDS) ? RFDS_MITIGATION_VERW : RFDS_MITIGATION_OFF;
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static const char * const rfds_strings[] = {
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[RFDS_MITIGATION_OFF] = "Vulnerable",
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[RFDS_MITIGATION_VERW] = "Mitigation: Clear Register File",
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[RFDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode",
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};
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static void __init rfds_select_mitigation(void)
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{
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if (!boot_cpu_has_bug(X86_BUG_RFDS) || cpu_mitigations_off()) {
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rfds_mitigation = RFDS_MITIGATION_OFF;
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return;
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}
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if (rfds_mitigation == RFDS_MITIGATION_OFF)
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return;
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if (x86_read_arch_cap_msr() & ARCH_CAP_RFDS_CLEAR)
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setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
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else
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rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
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}
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static __init int rfds_parse_cmdline(char *str)
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{
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if (!str)
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return -EINVAL;
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if (!boot_cpu_has_bug(X86_BUG_RFDS))
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return 0;
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if (!strcmp(str, "off"))
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rfds_mitigation = RFDS_MITIGATION_OFF;
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else if (!strcmp(str, "on"))
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rfds_mitigation = RFDS_MITIGATION_VERW;
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return 0;
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}
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early_param("reg_file_data_sampling", rfds_parse_cmdline);
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#undef pr_fmt
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#define pr_fmt(fmt) "" fmt
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@ -498,11 +556,19 @@ static void __init md_clear_update_mitigation(void)
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taa_mitigation = TAA_MITIGATION_VERW;
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taa_select_mitigation();
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}
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if (mmio_mitigation == MMIO_MITIGATION_OFF &&
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boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
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/*
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* MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
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* gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
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*/
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if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
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mmio_mitigation = MMIO_MITIGATION_VERW;
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mmio_select_mitigation();
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}
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if (rfds_mitigation == RFDS_MITIGATION_OFF &&
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boot_cpu_has_bug(X86_BUG_RFDS)) {
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rfds_mitigation = RFDS_MITIGATION_VERW;
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rfds_select_mitigation();
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}
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out:
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if (boot_cpu_has_bug(X86_BUG_MDS))
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pr_info("MDS: %s\n", mds_strings[mds_mitigation]);
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@ -512,6 +578,8 @@ out:
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pr_info("MMIO Stale Data: %s\n", mmio_strings[mmio_mitigation]);
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else if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
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pr_info("MMIO Stale Data: Unknown: No mitigations\n");
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if (boot_cpu_has_bug(X86_BUG_RFDS))
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pr_info("Register File Data Sampling: %s\n", rfds_strings[rfds_mitigation]);
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}
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static void __init md_clear_select_mitigation(void)
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@ -519,11 +587,12 @@ static void __init md_clear_select_mitigation(void)
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mds_select_mitigation();
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taa_select_mitigation();
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mmio_select_mitigation();
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rfds_select_mitigation();
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/*
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* As MDS, TAA and MMIO Stale Data mitigations are inter-related, update
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* and print their mitigation after MDS, TAA and MMIO Stale Data
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* mitigation selection is done.
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* As these mitigations are inter-related and rely on VERW instruction
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* to clear the microarchitural buffers, update and print their status
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* after mitigation selection is done for each of these vulnerabilities.
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*/
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md_clear_update_mitigation();
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}
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@ -2613,6 +2682,11 @@ static ssize_t mmio_stale_data_show_state(char *buf)
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sched_smt_active() ? "vulnerable" : "disabled");
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}
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static ssize_t rfds_show_state(char *buf)
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{
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return sysfs_emit(buf, "%s\n", rfds_strings[rfds_mitigation]);
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}
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static char *stibp_state(void)
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{
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if (spectre_v2_in_eibrs_mode(spectre_v2_enabled) &&
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@ -2772,6 +2846,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
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case X86_BUG_GDS:
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return gds_show_state(buf);
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case X86_BUG_RFDS:
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return rfds_show_state(buf);
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default:
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break;
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}
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@ -2846,6 +2923,11 @@ ssize_t cpu_show_gds(struct device *dev, struct device_attribute *attr, char *bu
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{
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return cpu_show_common(dev, attr, buf, X86_BUG_GDS);
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}
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ssize_t cpu_show_reg_file_data_sampling(struct device *dev, struct device_attribute *attr, char *buf)
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{
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return cpu_show_common(dev, attr, buf, X86_BUG_RFDS);
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}
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#endif
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void __warn_thunk(void)
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@ -1224,6 +1224,8 @@ static const __initconst struct x86_cpu_id cpu_vuln_whitelist[] = {
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#define SRSO BIT(5)
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/* CPU is affected by GDS */
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#define GDS BIT(6)
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/* CPU is affected by Register File Data Sampling */
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#define RFDS BIT(7)
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static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = {
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VULNBL_INTEL_STEPPINGS(IVYBRIDGE, X86_STEPPING_ANY, SRBDS),
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@ -1251,9 +1253,18 @@ static const struct x86_cpu_id cpu_vuln_blacklist[] __initconst = {
|
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VULNBL_INTEL_STEPPINGS(TIGERLAKE, X86_STEPPING_ANY, GDS),
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VULNBL_INTEL_STEPPINGS(LAKEFIELD, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RETBLEED),
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VULNBL_INTEL_STEPPINGS(ROCKETLAKE, X86_STEPPING_ANY, MMIO | RETBLEED | GDS),
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VULNBL_INTEL_STEPPINGS(ATOM_TREMONT, X86_STEPPING_ANY, MMIO | MMIO_SBDS),
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VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D, X86_STEPPING_ANY, MMIO),
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VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L, X86_STEPPING_ANY, MMIO | MMIO_SBDS),
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VULNBL_INTEL_STEPPINGS(ALDERLAKE, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ALDERLAKE_L, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(RAPTORLAKE, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(RAPTORLAKE_P, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(RAPTORLAKE_S, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_GRACEMONT, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_TREMONT, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_D, X86_STEPPING_ANY, MMIO | RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_TREMONT_L, X86_STEPPING_ANY, MMIO | MMIO_SBDS | RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT_D, X86_STEPPING_ANY, RFDS),
|
||||
VULNBL_INTEL_STEPPINGS(ATOM_GOLDMONT_PLUS, X86_STEPPING_ANY, RFDS),
|
||||
|
||||
VULNBL_AMD(0x15, RETBLEED),
|
||||
VULNBL_AMD(0x16, RETBLEED),
|
||||
@ -1287,6 +1298,24 @@ static bool arch_cap_mmio_immune(u64 ia32_cap)
|
||||
ia32_cap & ARCH_CAP_SBDR_SSDP_NO);
|
||||
}
|
||||
|
||||
static bool __init vulnerable_to_rfds(u64 ia32_cap)
|
||||
{
|
||||
/* The "immunity" bit trumps everything else: */
|
||||
if (ia32_cap & ARCH_CAP_RFDS_NO)
|
||||
return false;
|
||||
|
||||
/*
|
||||
* VMMs set ARCH_CAP_RFDS_CLEAR for processors not in the blacklist to
|
||||
* indicate that mitigation is needed because guest is running on a
|
||||
* vulnerable hardware or may migrate to such hardware:
|
||||
*/
|
||||
if (ia32_cap & ARCH_CAP_RFDS_CLEAR)
|
||||
return true;
|
||||
|
||||
/* Only consult the blacklist when there is no enumeration: */
|
||||
return cpu_matches(cpu_vuln_blacklist, RFDS);
|
||||
}
|
||||
|
||||
static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
|
||||
{
|
||||
u64 ia32_cap = x86_read_arch_cap_msr();
|
||||
@ -1403,6 +1432,9 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
|
||||
boot_cpu_has(X86_FEATURE_AVX))
|
||||
setup_force_cpu_bug(X86_BUG_GDS);
|
||||
|
||||
if (vulnerable_to_rfds(ia32_cap))
|
||||
setup_force_cpu_bug(X86_BUG_RFDS);
|
||||
|
||||
if (cpu_matches(cpu_vuln_whitelist, NO_MELTDOWN))
|
||||
return;
|
||||
|
||||
|
||||
@ -1623,7 +1623,8 @@ static bool kvm_is_immutable_feature_msr(u32 msr)
|
||||
ARCH_CAP_SKIP_VMENTRY_L1DFLUSH | ARCH_CAP_SSB_NO | ARCH_CAP_MDS_NO | \
|
||||
ARCH_CAP_PSCHANGE_MC_NO | ARCH_CAP_TSX_CTRL_MSR | ARCH_CAP_TAA_NO | \
|
||||
ARCH_CAP_SBDR_SSDP_NO | ARCH_CAP_FBSDP_NO | ARCH_CAP_PSDP_NO | \
|
||||
ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | ARCH_CAP_GDS_NO)
|
||||
ARCH_CAP_FB_CLEAR | ARCH_CAP_RRSBA | ARCH_CAP_PBRSB_NO | ARCH_CAP_GDS_NO | \
|
||||
ARCH_CAP_RFDS_NO | ARCH_CAP_RFDS_CLEAR)
|
||||
|
||||
static u64 kvm_get_arch_capabilities(void)
|
||||
{
|
||||
@ -1655,6 +1656,8 @@ static u64 kvm_get_arch_capabilities(void)
|
||||
data |= ARCH_CAP_SSB_NO;
|
||||
if (!boot_cpu_has_bug(X86_BUG_MDS))
|
||||
data |= ARCH_CAP_MDS_NO;
|
||||
if (!boot_cpu_has_bug(X86_BUG_RFDS))
|
||||
data |= ARCH_CAP_RFDS_NO;
|
||||
|
||||
if (!boot_cpu_has(X86_FEATURE_RTM)) {
|
||||
/*
|
||||
|
||||
@ -588,6 +588,7 @@ CPU_SHOW_VULN_FALLBACK(mmio_stale_data);
|
||||
CPU_SHOW_VULN_FALLBACK(retbleed);
|
||||
CPU_SHOW_VULN_FALLBACK(spec_rstack_overflow);
|
||||
CPU_SHOW_VULN_FALLBACK(gds);
|
||||
CPU_SHOW_VULN_FALLBACK(reg_file_data_sampling);
|
||||
|
||||
static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
|
||||
static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
|
||||
@ -602,6 +603,7 @@ static DEVICE_ATTR(mmio_stale_data, 0444, cpu_show_mmio_stale_data, NULL);
|
||||
static DEVICE_ATTR(retbleed, 0444, cpu_show_retbleed, NULL);
|
||||
static DEVICE_ATTR(spec_rstack_overflow, 0444, cpu_show_spec_rstack_overflow, NULL);
|
||||
static DEVICE_ATTR(gather_data_sampling, 0444, cpu_show_gds, NULL);
|
||||
static DEVICE_ATTR(reg_file_data_sampling, 0444, cpu_show_reg_file_data_sampling, NULL);
|
||||
|
||||
static struct attribute *cpu_root_vulnerabilities_attrs[] = {
|
||||
&dev_attr_meltdown.attr,
|
||||
@ -617,6 +619,7 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
|
||||
&dev_attr_retbleed.attr,
|
||||
&dev_attr_spec_rstack_overflow.attr,
|
||||
&dev_attr_gather_data_sampling.attr,
|
||||
&dev_attr_reg_file_data_sampling.attr,
|
||||
NULL
|
||||
};
|
||||
|
||||
|
||||
@ -75,6 +75,8 @@ extern ssize_t cpu_show_spec_rstack_overflow(struct device *dev,
|
||||
struct device_attribute *attr, char *buf);
|
||||
extern ssize_t cpu_show_gds(struct device *dev,
|
||||
struct device_attribute *attr, char *buf);
|
||||
extern ssize_t cpu_show_reg_file_data_sampling(struct device *dev,
|
||||
struct device_attribute *attr, char *buf);
|
||||
|
||||
extern __printf(4, 5)
|
||||
struct device *cpu_device_create(struct device *parent, void *drvdata,
|
||||
|
||||
Loading…
Reference in New Issue
Block a user