diff options
Diffstat (limited to 'Documentation/admin-guide/hw-vuln')
| -rw-r--r-- | Documentation/admin-guide/hw-vuln/attack_vector_controls.rst | 7 | ||||
| -rw-r--r-- | Documentation/admin-guide/hw-vuln/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/admin-guide/hw-vuln/vmscape.rst | 110 |
3 files changed, 113 insertions, 5 deletions
diff --git a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst index b4de16f5ec44..5964901d66e3 100644 --- a/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst +++ b/Documentation/admin-guide/hw-vuln/attack_vector_controls.rst @@ -214,8 +214,8 @@ Spectre_v1 X Spectre_v2 X X Spectre_v2_user X X * (Note 1) SRBDS X X X X -SRSO X X -SSB (Note 4) +SRSO X X X X +SSB X TAA X X X X * (Note 2) TSA X X X X =============== ============== ============ ============= ============== ============ ======== @@ -229,9 +229,6 @@ Notes: 3 -- Disables SMT if cross-thread mitigations are fully enabled, the CPU is vulnerable, and STIBP is not supported - 4 -- Speculative store bypass is always enabled by default (no kernel - mitigation applied) unless overridden with spec_store_bypass_disable option - When an attack-vector is disabled, all mitigations for the vulnerabilities listed in the above table are disabled, unless mitigation is required for a different enabled attack-vector or a mitigation is explicitly selected via a diff --git a/Documentation/admin-guide/hw-vuln/index.rst b/Documentation/admin-guide/hw-vuln/index.rst index 89ca636081b7..55d747511f83 100644 --- a/Documentation/admin-guide/hw-vuln/index.rst +++ b/Documentation/admin-guide/hw-vuln/index.rst @@ -26,3 +26,4 @@ are configurable at compile, boot or run time. rsb old_microcode indirect-target-selection + vmscape diff --git a/Documentation/admin-guide/hw-vuln/vmscape.rst b/Documentation/admin-guide/hw-vuln/vmscape.rst new file mode 100644 index 000000000000..d9b9a2b6c114 --- /dev/null +++ b/Documentation/admin-guide/hw-vuln/vmscape.rst @@ -0,0 +1,110 @@ +.. SPDX-License-Identifier: GPL-2.0 + +VMSCAPE +======= + +VMSCAPE is a vulnerability that may allow a guest to influence the branch +prediction in host userspace. It particularly affects hypervisors like QEMU. + +Even if a hypervisor may not have any sensitive data like disk encryption keys, +guest-userspace may be able to attack the guest-kernel using the hypervisor as +a confused deputy. + +Affected processors +------------------- + +The following CPU families are affected by VMSCAPE: + +**Intel processors:** + - Skylake generation (Parts without Enhanced-IBRS) + - Cascade Lake generation - (Parts affected by ITS guest/host separation) + - Alder Lake and newer (Parts affected by BHI) + +Note that, BHI affected parts that use BHB clearing software mitigation e.g. +Icelake are not vulnerable to VMSCAPE. + +**AMD processors:** + - Zen series (families 0x17, 0x19, 0x1a) + +** Hygon processors:** + - Family 0x18 + +Mitigation +---------- + +Conditional IBPB +---------------- + +Kernel tracks when a CPU has run a potentially malicious guest and issues an +IBPB before the first exit to userspace after VM-exit. If userspace did not run +between VM-exit and the next VM-entry, no IBPB is issued. + +Note that the existing userspace mitigation against Spectre-v2 is effective in +protecting the userspace. They are insufficient to protect the userspace VMMs +from a malicious guest. This is because Spectre-v2 mitigations are applied at +context switch time, while the userspace VMM can run after a VM-exit without a +context switch. + +Vulnerability enumeration and mitigation is not applied inside a guest. This is +because nested hypervisors should already be deploying IBPB to isolate +themselves from nested guests. + +SMT considerations +------------------ + +When Simultaneous Multi-Threading (SMT) is enabled, hypervisors can be +vulnerable to cross-thread attacks. For complete protection against VMSCAPE +attacks in SMT environments, STIBP should be enabled. + +The kernel will issue a warning if SMT is enabled without adequate STIBP +protection. Warning is not issued when: + +- SMT is disabled +- STIBP is enabled system-wide +- Intel eIBRS is enabled (which implies STIBP protection) + +System information and options +------------------------------ + +The sysfs file showing VMSCAPE mitigation status is: + + /sys/devices/system/cpu/vulnerabilities/vmscape + +The possible values in this file are: + + * 'Not affected': + + The processor is not vulnerable to VMSCAPE attacks. + + * 'Vulnerable': + + The processor is vulnerable and no mitigation has been applied. + + * 'Mitigation: IBPB before exit to userspace': + + Conditional IBPB mitigation is enabled. The kernel tracks when a CPU has + run a potentially malicious guest and issues an IBPB before the first + exit to userspace after VM-exit. + + * 'Mitigation: IBPB on VMEXIT': + + IBPB is issued on every VM-exit. This occurs when other mitigations like + RETBLEED or SRSO are already issuing IBPB on VM-exit. + +Mitigation control on the kernel command line +---------------------------------------------- + +The mitigation can be controlled via the ``vmscape=`` command line parameter: + + * ``vmscape=off``: + + Disable the VMSCAPE mitigation. + + * ``vmscape=ibpb``: + + Enable conditional IBPB mitigation (default when CONFIG_MITIGATION_VMSCAPE=y). + + * ``vmscape=force``: + + Force vulnerability detection and mitigation even on processors that are + not known to be affected. |