I'm attaching a backport that should work for all of 5.10, 5.15, and 5.18. Ben. -- Ben Hutchings Larkinson's Law: All laws are basically false.
From 999bc23969f190ec9aa54a0ca20a8c94e2d67ba1 Mon Sep 17 00:00:00 2001
From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Date: Sat, 23 Jul 2022 17:22:47 +0200
Subject: [PATCH] x86/speculation: Make all RETbleed mitigations 64-bit only
commit b648ab487f31bc4c38941bc770ea97fe394304bb upstream.
The mitigations for RETBleed are currently ineffective on x86_32 since
entry_32.S does not use the required macros. However, for an x86_32
target, the kconfig symbols for them are still enabled by default and
/sys/devices/system/cpu/vulnerabilities/retbleed will wrongly report
that mitigations are in place.
Make all of these symbols depend on X86_64, and only enable RETHUNK by
default on X86_64.
Fixes: f43b9876e857 ("x86/retbleed: Add fine grained Kconfig knobs")
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/YtwSR3NNsWp1ohfV@xxxxxxxxxxxxxxx
[bwh: Backported to 5.10/5.15/5.18: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
arch/x86/Kconfig | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 4d1d87f76a74..ce1f5a876cfe 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2469,7 +2469,7 @@ config RETPOLINE
config RETHUNK
bool "Enable return-thunks"
depends on RETPOLINE && CC_HAS_RETURN_THUNK
- default y
+ default y if X86_64
help
Compile the kernel with the return-thunks compiler option to guard
against kernel-to-user data leaks by avoiding return speculation.
@@ -2478,21 +2478,21 @@ config RETHUNK
config CPU_UNRET_ENTRY
bool "Enable UNRET on kernel entry"
- depends on CPU_SUP_AMD && RETHUNK
+ depends on CPU_SUP_AMD && RETHUNK && X86_64
default y
help
Compile the kernel with support for the retbleed=unret mitigation.
config CPU_IBPB_ENTRY
bool "Enable IBPB on kernel entry"
- depends on CPU_SUP_AMD
+ depends on CPU_SUP_AMD && X86_64
default y
help
Compile the kernel with support for the retbleed=ibpb mitigation.
config CPU_IBRS_ENTRY
bool "Enable IBRS on kernel entry"
- depends on CPU_SUP_INTEL
+ depends on CPU_SUP_INTEL && X86_64
default y
help
Compile the kernel with support for the spectre_v2=ibrs mitigation.
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