linux-kernel - [PATCH v2 16/35] x86/bugs: Restructure ssb mitigation

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Message-ID: <20241105215455.359471-17-david.kaplan@amd.com>
Date: Tue, 5 Nov 2024 15:54:36 -0600
From: David Kaplan <david.kaplan@....com>
To: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar
	<mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H . Peter Anvin" <hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 16/35] x86/bugs: Restructure ssb mitigation

Restructure ssb to use select/apply functions to create consistent
vulnerability handling.

Remove __ssb_select_mitigation() and split the functionality between the
select/apply functions.

Signed-off-by: David Kaplan <david.kaplan@....com>
---
 arch/x86/kernel/cpu/bugs.c | 34 ++++++++++++++++------------------
 1 file changed, 16 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ec5cc66513bd..a3bbb0831845 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -65,6 +65,7 @@ static void __init spectre_v2_user_select_mitigation(void);
 static void __init spectre_v2_user_update_mitigation(void);
 static void __init spectre_v2_user_apply_mitigation(void);
 static void __init ssb_select_mitigation(void);
+static void __init ssb_apply_mitigation(void);
 static void __init l1tf_select_mitigation(void);
 static void __init mds_select_mitigation(void);
 static void __init mds_update_mitigation(void);
@@ -223,6 +224,7 @@ void __init cpu_select_mitigations(void)
 	spectre_v2_apply_mitigation();
 	retbleed_apply_mitigation();
 	spectre_v2_user_apply_mitigation();
+	ssb_apply_mitigation();
 	mds_apply_mitigation();
 	taa_apply_mitigation();
 	mmio_apply_mitigation();
@@ -2214,19 +2216,18 @@ static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
 	return cmd;
 }
 
-static enum ssb_mitigation __init __ssb_select_mitigation(void)
+static void ssb_select_mitigation(void)
 {
-	enum ssb_mitigation mode = SPEC_STORE_BYPASS_NONE;
 	enum ssb_mitigation_cmd cmd;
 
 	if (!boot_cpu_has(X86_FEATURE_SSBD))
-		return mode;
+		return;
 
 	cmd = ssb_parse_cmdline();
 	if (!boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS) &&
 	    (cmd == SPEC_STORE_BYPASS_CMD_NONE ||
 	     cmd == SPEC_STORE_BYPASS_CMD_AUTO))
-		return mode;
+		return;
 
 	switch (cmd) {
 	case SPEC_STORE_BYPASS_CMD_SECCOMP:
@@ -2235,28 +2236,34 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 		 * enabled.
 		 */
 		if (IS_ENABLED(CONFIG_SECCOMP))
-			mode = SPEC_STORE_BYPASS_SECCOMP;
+			ssb_mode = SPEC_STORE_BYPASS_SECCOMP;
 		else
-			mode = SPEC_STORE_BYPASS_PRCTL;
+			ssb_mode = SPEC_STORE_BYPASS_PRCTL;
 		break;
 	case SPEC_STORE_BYPASS_CMD_ON:
-		mode = SPEC_STORE_BYPASS_DISABLE;
+		ssb_mode = SPEC_STORE_BYPASS_DISABLE;
 		break;
 	case SPEC_STORE_BYPASS_CMD_AUTO:
 	case SPEC_STORE_BYPASS_CMD_PRCTL:
-		mode = SPEC_STORE_BYPASS_PRCTL;
+		ssb_mode = SPEC_STORE_BYPASS_PRCTL;
 		break;
 	case SPEC_STORE_BYPASS_CMD_NONE:
 		break;
 	}
 
+	if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
+		pr_info("%s\n", ssb_strings[ssb_mode]);
+}
+
+static void __init ssb_apply_mitigation(void)
+{
 	/*
 	 * We have three CPU feature flags that are in play here:
 	 *  - X86_BUG_SPEC_STORE_BYPASS - CPU is susceptible.
 	 *  - X86_FEATURE_SSBD - CPU is able to turn off speculative store bypass
 	 *  - X86_FEATURE_SPEC_STORE_BYPASS_DISABLE - engage the mitigation
 	 */
-	if (mode == SPEC_STORE_BYPASS_DISABLE) {
+	if (ssb_mode == SPEC_STORE_BYPASS_DISABLE) {
 		setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE);
 		/*
 		 * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may
@@ -2271,15 +2278,6 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 		}
 	}
 
-	return mode;
-}
-
-static void ssb_select_mitigation(void)
-{
-	ssb_mode = __ssb_select_mitigation();
-
-	if (boot_cpu_has_bug(X86_BUG_SPEC_STORE_BYPASS))
-		pr_info("%s\n", ssb_strings[ssb_mode]);
 }
 
 #undef pr_fmt
-- 
2.34.1