x86/speculation: Make all RETbleed mitigations 64-bit only

BugLink: https://bugs.launchpad.net/bugs/1989221
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@decadent.org.uk>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: <stable@vger.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@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e898391367c010715eb6c9335b9728a10cf8c56b..6aa01a3b8495f6691f5c5567bb261350a01441ad 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2444,7 +2444,7 @@ 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.
@@ -2453,21 +2453,21 @@ 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.