diff options
| author | Pawan Gupta <pawan.kumar.gupta@linux.intel.com> | 2024-06-22 06:23:23 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-05-18 09:24:11 +0300 |
| commit | f7ef7f6ccf2bc3909ef5e50cbe9edf2bac71e1bd (patch) | |
| tree | 730df1c7a99069506bf2e4be5212c2edc0d72087 /Documentation/ABI | |
| parent | 4754e29f43c63adb42da1300dea4d8c1ac121c98 (diff) | |
| download | linux-f7ef7f6ccf2bc3909ef5e50cbe9edf2bac71e1bd.tar.xz | |
x86/its: Enable Indirect Target Selection mitigation
commit f4818881c47fd91fcb6d62373c57c7844e3de1c0 upstream.
Indirect Target Selection (ITS) is a bug in some pre-ADL Intel CPUs with
eIBRS. It affects prediction of indirect branch and RETs in the
lower half of cacheline. Due to ITS such branches may get wrongly predicted
to a target of (direct or indirect) branch that is located in the upper
half of the cacheline.
Scope of impact
===============
Guest/host isolation
--------------------
When eIBRS is used for guest/host isolation, the indirect branches in the
VMM may still be predicted with targets corresponding to branches in the
guest.
Intra-mode
----------
cBPF or other native gadgets can be used for intra-mode training and
disclosure using ITS.
User/kernel isolation
---------------------
When eIBRS is enabled user/kernel isolation is not impacted.
Indirect Branch Prediction Barrier (IBPB)
-----------------------------------------
After an IBPB, indirect branches may be predicted with targets
corresponding to direct branches which were executed prior to IBPB. This is
mitigated by a microcode update.
Add cmdline parameter indirect_target_selection=off|on|force to control the
mitigation to relocate the affected branches to an ITS-safe thunk i.e.
located in the upper half of cacheline. Also add the sysfs reporting.
When retpoline mitigation is deployed, ITS safe-thunks are not needed,
because retpoline sequence is already ITS-safe. Similarly, when call depth
tracking (CDT) mitigation is deployed (retbleed=stuff), ITS safe return
thunk is not used, as CDT prevents RSB-underflow.
To not overcomplicate things, ITS mitigation is not supported with
spectre-v2 lfence;jmp mitigation. Moreover, it is less practical to deploy
lfence;jmp mitigation on ITS affected parts anyways.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/ABI')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-devices-system-cpu | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 657bdee28d84..0426ec112155 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -514,6 +514,7 @@ Description: information about CPUs heterogeneity. What: /sys/devices/system/cpu/vulnerabilities /sys/devices/system/cpu/vulnerabilities/gather_data_sampling + /sys/devices/system/cpu/vulnerabilities/indirect_target_selection /sys/devices/system/cpu/vulnerabilities/itlb_multihit /sys/devices/system/cpu/vulnerabilities/l1tf /sys/devices/system/cpu/vulnerabilities/mds |