[PATCH v3 07/10] x86/bugs: Add a separate config for Spectre v1

[Breno Leitao]

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 Spectre v1 CPU mitigation under
CONFIG_SPECULATION_MITIGATIONS. This allow users to enable or disable
it at compilation time.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
 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 f5c941a0a837..43dd45720fb1 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2708,6 +2708,16 @@ config MITIGATION_RETBLEED
 	  unprivileged attacker can use these flaws to bypass conventional
 	  memory security restrictions to gain read access to privileged memory
 	  that would otherwise be inaccessible.
+
+config MITIGATION_SPECTRE_V1
+	bool "Mitigate SPECTRE V1 hardware bug"
+	default y
+	help
+	  Enable mitigation for Spectre V1 (Bounds Check Bypass). Spectre V1 is a
+	  class of side channel attacks that takes advantage of speculative
+	  execution that bypasses conditional branch instructions used for
+	  memory access bounds check.
+	  See also <file:Documentation/admin-guide/hw-vuln/spectre.rst>
 endif
 
 config ARCH_HAS_ADD_PAGES
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index c6c404b1c6ac..00c3438519be 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -875,7 +875,8 @@ enum spectre_v1_mitigation {
 };
 
 static enum spectre_v1_mitigation spectre_v1_mitigation __ro_after_init =
-	SPECTRE_V1_MITIGATION_AUTO;
+	IS_ENABLED(CONFIG_MITIGATION_SPECTRE_V1) ?
+		SPECTRE_V1_MITIGATION_AUTO : SPECTRE_V1_MITIGATION_NONE;
 
 static const char * const spectre_v1_strings[] = {
 	[SPECTRE_V1_MITIGATION_NONE] = "Vulnerable: __user pointer sanitization and usercopy barriers only; no swapgs barriers",
-- 
2.43.0