x86/bugs: Add a separate config for RETBLEED

Currently, the CONFIG_SPECULATION_MITIGATIONS is halfway populated,
where some mitigations have entries in Kconfig, and they could be
modified, while others mitigations do not have Kconfig entries, and
could not be controlled at build time.

Create an entry for the RETBLEED CPU mitigation under
CONFIG_SPECULATION_MITIGATIONS. This allow users to enable or disable
it at compilation time.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/20240729164105.554296-6-leitao@debian.org

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 290f0865fd85cbee58b8515fb73bdec18ad1ebdf..c9a9f928dddf2b193fbfa45856f96f9b359c9413 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2692,6 +2692,19 @@ config MITIGATION_L1TF
          hardware vulnerability which allows unprivileged speculative access to data
          available in the Level 1 Data Cache.
          See <file:Documentation/admin-guide/hw-vuln/l1tf.rst
+
+config MITIGATION_RETBLEED
+       bool "Mitigate RETBleed hardware bug"
+       depends on (CPU_SUP_INTEL && MITIGATION_SPECTRE_V2) || MITIGATION_UNRET_ENTRY || MITIGATION_IBPB_ENTRY
+       default y
+       help
+         Enable mitigation for RETBleed (Arbitrary Speculative Code Execution
+         with Return Instructions) vulnerability.  RETBleed is a speculative
+         execution attack which takes advantage of microarchitectural behavior
+         in many modern microprocessors, similar to Spectre v2. An
+         unprivileged attacker can use these flaws to bypass conventional
+         memory security restrictions to gain read access to privileged memory
+         that would otherwise be inaccessible.
 endif
 
 config ARCH_HAS_ADD_PAGES

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4fde9bd368ad49af335a70b0e4e7f755c7812e0c..08edca8c2c1faa6d154abc83637e320c4e606a82 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -989,7 +989,7 @@ static const char * const retbleed_strings[] = {
 static enum retbleed_mitigation retbleed_mitigation __ro_after_init =
        RETBLEED_MITIGATION_NONE;
 static enum retbleed_mitigation_cmd retbleed_cmd __ro_after_init =
-       RETBLEED_CMD_AUTO;
+       IS_ENABLED(CONFIG_MITIGATION_RETBLEED) ? RETBLEED_CMD_AUTO : RETBLEED_CMD_OFF;
 
 static int __ro_after_init retbleed_nosmt = false;