x86/bugs: Add a separate config for L1TF

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 L1TF 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/20240729164105.554296-5-leitao@debian.org

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b169677ec4ac7d712d3a68d2e403b29ac6683516..290f0865fd85cbee58b8515fb73bdec18ad1ebdf 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2682,6 +2682,16 @@ config MITIGATION_MMIO_STALE_DATA
          attacker to have access to MMIO.
          See also
          <file:Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst>
+
+config MITIGATION_L1TF
+       bool "Mitigate L1 Terminal Fault (L1TF) hardware bug"
+       depends on CPU_SUP_INTEL
+       default y
+       help
+         Mitigate L1 Terminal Fault (L1TF) hardware bug. L1 Terminal Fault is a
+         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
 endif
 
 config ARCH_HAS_ADD_PAGES

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 9b0d058f3fe847ca4b76378452848c811b938efe..4fde9bd368ad49af335a70b0e4e7f755c7812e0c 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2374,7 +2374,8 @@ EXPORT_SYMBOL_GPL(itlb_multihit_kvm_mitigation);
 #define pr_fmt(fmt)    "L1TF: " fmt
 
 /* Default mitigation for L1TF-affected CPUs */
-enum l1tf_mitigations l1tf_mitigation __ro_after_init = L1TF_MITIGATION_FLUSH;
+enum l1tf_mitigations l1tf_mitigation __ro_after_init =
+       IS_ENABLED(CONFIG_MITIGATION_L1TF) ? L1TF_MITIGATION_FLUSH : L1TF_MITIGATION_OFF;
 #if IS_ENABLED(CONFIG_KVM_INTEL)
 EXPORT_SYMBOL_GPL(l1tf_mitigation);
 #endif