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authorPhilippe Schenker <philippe.schenker@toradex.com>2022-05-19 14:57:48 +0200
committerPhilippe Schenker <philippe.schenker@toradex.com>2022-05-19 14:57:48 +0200
commit0e61b511dd8474280ba674590daa55f30433b7d4 (patch)
tree48c35f63dc1101d0d528b5d79c81849b99ca7c6d /Documentation/admin-guide
parentc4bda7fe18b3ff6898f8fa110a3d60ee8f4379a0 (diff)
parent01565c91b789a1612051e735a65f11096a6f08e8 (diff)
Merge tag 'v5.4.193' into update-to-2.3.7__5.4-2.3.x-imx
This is the 5.4.193 stable release Conflicts: arch/arm64/boot/dts/freescale/fsl-ls1028a-qds.dts drivers/edac/synopsys_edac.c drivers/mmc/host/sdhci-esdhc-imx.c drivers/mmc/host/sdhci.c drivers/mtd/nand/raw/gpmi-nand/gpmi-nand.c sound/soc/codecs/msm8916-wcd-analog.c
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/hw-vuln/spectre.rst50
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt18
-rw-r--r--Documentation/admin-guide/sysctl/kernel.rst21
3 files changed, 68 insertions, 21 deletions
diff --git a/Documentation/admin-guide/hw-vuln/spectre.rst b/Documentation/admin-guide/hw-vuln/spectre.rst
index e05e581af5cf..6bd97cd50d62 100644
--- a/Documentation/admin-guide/hw-vuln/spectre.rst
+++ b/Documentation/admin-guide/hw-vuln/spectre.rst
@@ -60,8 +60,8 @@ privileged data touched during the speculative execution.
Spectre variant 1 attacks take advantage of speculative execution of
conditional branches, while Spectre variant 2 attacks use speculative
execution of indirect branches to leak privileged memory.
-See :ref:`[1] <spec_ref1>` :ref:`[5] <spec_ref5>` :ref:`[7] <spec_ref7>`
-:ref:`[10] <spec_ref10>` :ref:`[11] <spec_ref11>`.
+See :ref:`[1] <spec_ref1>` :ref:`[5] <spec_ref5>` :ref:`[6] <spec_ref6>`
+:ref:`[7] <spec_ref7>` :ref:`[10] <spec_ref10>` :ref:`[11] <spec_ref11>`.
Spectre variant 1 (Bounds Check Bypass)
---------------------------------------
@@ -131,6 +131,19 @@ steer its indirect branch speculations to gadget code, and measure the
speculative execution's side effects left in level 1 cache to infer the
victim's data.
+Yet another variant 2 attack vector is for the attacker to poison the
+Branch History Buffer (BHB) to speculatively steer an indirect branch
+to a specific Branch Target Buffer (BTB) entry, even if the entry isn't
+associated with the source address of the indirect branch. Specifically,
+the BHB might be shared across privilege levels even in the presence of
+Enhanced IBRS.
+
+Currently the only known real-world BHB attack vector is via
+unprivileged eBPF. Therefore, it's highly recommended to not enable
+unprivileged eBPF, especially when eIBRS is used (without retpolines).
+For a full mitigation against BHB attacks, it's recommended to use
+retpolines (or eIBRS combined with retpolines).
+
Attack scenarios
----------------
@@ -364,13 +377,15 @@ The possible values in this file are:
- Kernel status:
- ==================================== =================================
- 'Not affected' The processor is not vulnerable
- 'Vulnerable' Vulnerable, no mitigation
- 'Mitigation: Full generic retpoline' Software-focused mitigation
- 'Mitigation: Full AMD retpoline' AMD-specific software mitigation
- 'Mitigation: Enhanced IBRS' Hardware-focused mitigation
- ==================================== =================================
+ ======================================== =================================
+ 'Not affected' The processor is not vulnerable
+ 'Mitigation: None' Vulnerable, no mitigation
+ 'Mitigation: Retpolines' Use Retpoline thunks
+ 'Mitigation: LFENCE' Use LFENCE instructions
+ 'Mitigation: Enhanced IBRS' Hardware-focused mitigation
+ 'Mitigation: Enhanced IBRS + Retpolines' Hardware-focused + Retpolines
+ 'Mitigation: Enhanced IBRS + LFENCE' Hardware-focused + LFENCE
+ ======================================== =================================
- Firmware status: Show if Indirect Branch Restricted Speculation (IBRS) is
used to protect against Spectre variant 2 attacks when calling firmware (x86 only).
@@ -468,7 +483,7 @@ Spectre variant 2
before invoking any firmware code to prevent Spectre variant 2 exploits
using the firmware.
- Using kernel address space randomization (CONFIG_RANDOMIZE_SLAB=y
+ Using kernel address space randomization (CONFIG_RANDOMIZE_BASE=y
and CONFIG_SLAB_FREELIST_RANDOM=y in the kernel configuration) makes
attacks on the kernel generally more difficult.
@@ -584,12 +599,13 @@ kernel command line.
Specific mitigations can also be selected manually:
- retpoline
- replace indirect branches
- retpoline,generic
- google's original retpoline
- retpoline,amd
- AMD-specific minimal thunk
+ retpoline auto pick between generic,lfence
+ retpoline,generic Retpolines
+ retpoline,lfence LFENCE; indirect branch
+ retpoline,amd alias for retpoline,lfence
+ eibrs enhanced IBRS
+ eibrs,retpoline enhanced IBRS + Retpolines
+ eibrs,lfence enhanced IBRS + LFENCE
Not specifying this option is equivalent to
spectre_v2=auto.
@@ -730,7 +746,7 @@ AMD white papers:
.. _spec_ref6:
-[6] `Software techniques for managing speculation on AMD processors <https://developer.amd.com/wp-content/resources/90343-B_SoftwareTechniquesforManagingSpeculation_WP_7-18Update_FNL.pdf>`_.
+[6] `Software techniques for managing speculation on AMD processors <https://developer.amd.com/wp-content/resources/Managing-Speculation-on-AMD-Processors.pdf>`_.
ARM white papers:
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b11e1fd95ee5..979423e1b639 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1487,6 +1487,8 @@
architectures force reset to be always executed
i8042.unlock [HW] Unlock (ignore) the keylock
i8042.kbdreset [HW] Reset device connected to KBD port
+ i8042.probe_defer
+ [HW] Allow deferred probing upon i8042 probe errors
i810= [HW,DRM]
@@ -2112,8 +2114,12 @@
Default is 1 (enabled)
kvm-intel.emulate_invalid_guest_state=
- [KVM,Intel] Enable emulation of invalid guest states
- Default is 0 (disabled)
+ [KVM,Intel] Disable emulation of invalid guest state.
+ Ignored if kvm-intel.enable_unrestricted_guest=1, as
+ guest state is never invalid for unrestricted guests.
+ This param doesn't apply to nested guests (L2), as KVM
+ never emulates invalid L2 guest state.
+ Default is 1 (enabled)
kvm-intel.flexpriority=
[KVM,Intel] Disable FlexPriority feature (TPR shadow).
@@ -4487,8 +4493,12 @@
Specific mitigations can also be selected manually:
retpoline - replace indirect branches
- retpoline,generic - google's original retpoline
- retpoline,amd - AMD-specific minimal thunk
+ retpoline,generic - Retpolines
+ retpoline,lfence - LFENCE; indirect branch
+ retpoline,amd - alias for retpoline,lfence
+ eibrs - enhanced IBRS
+ eibrs,retpoline - enhanced IBRS + Retpolines
+ eibrs,lfence - enhanced IBRS + LFENCE
Not specifying this option is equivalent to
spectre_v2=auto.
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 032c7cd3cede..7b477fa19534 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1125,6 +1125,27 @@ NMI switch that most IA32 servers have fires unknown NMI up, for
example. If a system hangs up, try pressing the NMI switch.
+unprivileged_bpf_disabled:
+==========================
+
+Writing 1 to this entry will disable unprivileged calls to ``bpf()``;
+once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` will return
+``-EPERM``. Once set to 1, this can't be cleared from the running kernel
+anymore.
+
+Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,
+however, an admin can still change this setting later on, if needed, by
+writing 0 or 1 to this entry.
+
+If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this
+entry will default to 2 instead of 0.
+
+= =============================================================
+0 Unprivileged calls to ``bpf()`` are enabled
+1 Unprivileged calls to ``bpf()`` are disabled without recovery
+2 Unprivileged calls to ``bpf()`` are disabled
+= =============================================================
+
watchdog:
=========