linux-kernel - [PATCH 5.15 01/30] x86/speculation: Make all RETbleed mitigations 64-bit only

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Message-Id: <20220809175514.322531397@linuxfoundation.org>
Date:   Tue,  9 Aug 2022 20:00:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>,
        Borislav Petkov <bp@...e.de>
Subject: [PATCH 5.15 01/30] x86/speculation: Make all RETbleed mitigations 64-bit only

From: Ben Hutchings <ben@...adent.org.uk>

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@...adent.org.uk>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: <stable@...r.kernel.org>
Link: https://lore.kernel.org/r/YtwSR3NNsWp1ohfV@decadent.org.uk
[bwh: Backported to 5.10/5.15/5.18: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/Kconfig |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2427,7 +2427,7 @@ 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.
@@ -2436,21 +2436,21 @@ 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.