linux-kernel - [PATCH v3 05/10] x86/bugs: Add a separate config for L1TF

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Date: Mon, 22 Apr 2024 09:58:19 -0700
From: Breno Leitao <leitao@...ian.org>
To: jpoimboe@...nel.org,
	mingo@...hat.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH v3 05/10] 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@...ian.org>
Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 arch/x86/Kconfig           | 10 ++++++++++
 arch/x86/kernel/cpu/bugs.c |  3 ++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bba5b65034dc..192d20348b41 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2685,6 +2685,16 @@ 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 21daaf202b7f..d20299b350d7 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -2373,7 +2373,8 @@ 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
-- 
2.43.0