linux-kernel - [PATCH] x86/speculation: Make all RETbleed mitigations depend on X86

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Message-ID: <YtwSR3NNsWp1ohfV@decadent.org.uk>
Date:   Sat, 23 Jul 2022 17:22:47 +0200
From:   Ben Hutchings <ben@...adent.org.uk>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] x86/speculation: Make all RETbleed mitigations depend on
 X86_64

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.

Cc: stable@...r.kernel.org
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/x86/Kconfig | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e58798f636d4..1670a3fed263 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2473,7 +2473,7 @@ config RETHUNK
 	bool "Enable return-thunks"
 	depends on RETPOLINE && CC_HAS_RETURN_THUNK
 	select OBJTOOL if HAVE_OBJTOOL
-	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.
@@ -2482,21 +2482,21 @@ 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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