x86/bugs: Add a separate config for MMIO Stable Data

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 MMIO Stale data 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/20240729164105.554296-4-leitao@debian.org

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 712a4f8cb7dd05ba7df41a190e163e4ca05a318b..b169677ec4ac7d712d3a68d2e403b29ac6683516 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2670,6 +2670,18 @@ config MITIGATION_TAA
          which is available in various CPU internal buffers by using
          asynchronous aborts within an Intel TSX transactional region.
          See also <file:Documentation/admin-guide/hw-vuln/tsx_async_abort.rst>
+
+config MITIGATION_MMIO_STALE_DATA
+       bool "Mitigate MMIO Stale Data hardware bug"
+       depends on CPU_SUP_INTEL
+       default y
+       help
+         Enable mitigation for MMIO Stale Data hardware bugs.  Processor MMIO
+         Stale Data Vulnerabilities are a class of memory-mapped I/O (MMIO)
+         vulnerabilities that can expose data. The vulnerabilities require the
+         attacker to have access to MMIO.
+         See also
+         <file:Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst>
 endif
 
 config ARCH_HAS_ADD_PAGES

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ab306986762dd500cbd03082055702f52a934967..9b0d058f3fe847ca4b76378452848c811b938efe 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -393,7 +393,8 @@ enum mmio_mitigations {
 };
 
 /* Default mitigation for Processor MMIO Stale Data vulnerabilities */
-static enum mmio_mitigations mmio_mitigation __ro_after_init = MMIO_MITIGATION_VERW;
+static enum mmio_mitigations mmio_mitigation __ro_after_init =
+       IS_ENABLED(CONFIG_MITIGATION_MMIO_STALE_DATA) ? MMIO_MITIGATION_VERW : MMIO_MITIGATION_OFF;
 static bool mmio_nosmt __ro_after_init = false;
 
 static const char * const mmio_strings[] = {