[RFC PATCH 17/34] x86/bugs: Restructure srso mitigation

[David Kaplan <david.kaplan@amd.com>]

Restructure srso to use select/update/apply functions to create
consistent vulnerability handling.  Like with retbleed, the command line
options directly select mitigations which can later be modified.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 136 ++++++++++++++++++-------------------
 1 file changed, 68 insertions(+), 68 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ba10aa37d949..334fd2c5251d 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -84,6 +84,8 @@ static void __init srbds_select_mitigation(void);
 static void __init srbds_apply_mitigation(void);
 static void __init l1d_flush_select_mitigation(void);
 static void __init srso_select_mitigation(void);
+static void __init srso_update_mitigation(void);
+static void __init srso_apply_mitigation(void);
 static void __init gds_select_mitigation(void);
 static void __init gds_apply_mitigation(void);
 static void __init bhi_select_mitigation(void);
@@ -200,11 +202,6 @@ void __init cpu_select_mitigations(void)
 	rfds_select_mitigation();
 	srbds_select_mitigation();
 	l1d_flush_select_mitigation();
-
-	/*
-	 * srso_select_mitigation() depends and must run after
-	 * retbleed_select_mitigation().
-	 */
 	srso_select_mitigation();
 	gds_select_mitigation();
 	bhi_select_mitigation();
@@ -220,6 +217,7 @@ void __init cpu_select_mitigations(void)
 	taa_update_mitigation();
 	mmio_update_mitigation();
 	rfds_update_mitigation();
+	srso_update_mitigation();
 
 	spectre_v1_apply_mitigation();
 	spectre_v2_apply_mitigation();
@@ -232,6 +230,7 @@ void __init cpu_select_mitigations(void)
 	mmio_apply_mitigation();
 	rfds_apply_mitigation();
 	srbds_apply_mitigation();
+	srso_apply_mitigation();
 	gds_apply_mitigation();
 	bhi_apply_mitigation();
 }
@@ -2637,6 +2636,7 @@ early_param("l1tf", l1tf_cmdline);
 
 enum srso_mitigation {
 	SRSO_MITIGATION_NONE,
+	SRSO_MITIGATION_AUTO,
 	SRSO_MITIGATION_UCODE_NEEDED,
 	SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED,
 	SRSO_MITIGATION_MICROCODE,
@@ -2645,14 +2645,6 @@ enum srso_mitigation {
 	SRSO_MITIGATION_IBPB_ON_VMEXIT,
 };
 
-enum srso_mitigation_cmd {
-	SRSO_CMD_OFF,
-	SRSO_CMD_MICROCODE,
-	SRSO_CMD_SAFE_RET,
-	SRSO_CMD_IBPB,
-	SRSO_CMD_IBPB_ON_VMEXIT,
-};
-
 static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_NONE]			= "Vulnerable",
 	[SRSO_MITIGATION_UCODE_NEEDED]		= "Vulnerable: No microcode",
@@ -2663,8 +2655,7 @@ static const char * const srso_strings[] = {
 	[SRSO_MITIGATION_IBPB_ON_VMEXIT]	= "Mitigation: IBPB on VMEXIT only"
 };
 
-static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_NONE;
-static enum srso_mitigation_cmd srso_cmd __ro_after_init = SRSO_CMD_SAFE_RET;
+static enum srso_mitigation srso_mitigation __ro_after_init = SRSO_MITIGATION_AUTO;
 
 static int __init srso_parse_cmdline(char *str)
 {
@@ -2672,15 +2663,15 @@ static int __init srso_parse_cmdline(char *str)
 		return -EINVAL;
 
 	if (!strcmp(str, "off"))
-		srso_cmd = SRSO_CMD_OFF;
+		srso_mitigation = SRSO_MITIGATION_NONE;
 	else if (!strcmp(str, "microcode"))
-		srso_cmd = SRSO_CMD_MICROCODE;
+		srso_mitigation = SRSO_MITIGATION_MICROCODE;
 	else if (!strcmp(str, "safe-ret"))
-		srso_cmd = SRSO_CMD_SAFE_RET;
+		srso_mitigation = SRSO_MITIGATION_SAFE_RET;
 	else if (!strcmp(str, "ibpb"))
-		srso_cmd = SRSO_CMD_IBPB;
+		srso_mitigation = SRSO_MITIGATION_IBPB;
 	else if (!strcmp(str, "ibpb-vmexit"))
-		srso_cmd = SRSO_CMD_IBPB_ON_VMEXIT;
+		srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
 	else
 		pr_err("Ignoring unknown SRSO option (%s).", str);
 
@@ -2696,12 +2687,16 @@ static void __init srso_select_mitigation(void)
 
 	if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
 	    cpu_mitigations_off() ||
-	    srso_cmd == SRSO_CMD_OFF) {
+	    srso_mitigation == SRSO_MITIGATION_NONE) {
 		if (boot_cpu_has(X86_FEATURE_SBPB))
 			x86_pred_cmd = PRED_CMD_SBPB;
 		return;
 	}
 
+	/* Default mitigation */
+	if (srso_mitigation == SRSO_MITIGATION_AUTO)
+		srso_mitigation = SRSO_MITIGATION_SAFE_RET;
+
 	if (has_microcode) {
 		/*
 		 * Zen1/2 with SMT off aren't vulnerable after the right
@@ -2713,29 +2708,59 @@ static void __init srso_select_mitigation(void)
 			setup_force_cpu_cap(X86_FEATURE_SRSO_NO);
 			return;
 		}
-
-		if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB) {
-			srso_mitigation = SRSO_MITIGATION_IBPB;
-			goto out;
-		}
 	} else {
 		pr_warn("IBPB-extending microcode not applied!\n");
 		pr_warn(SRSO_NOTICE);
 
-		/* may be overwritten by SRSO_CMD_SAFE_RET below */
-		srso_mitigation = SRSO_MITIGATION_UCODE_NEEDED;
+		/* Fall-back to Safe-RET */
+		srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
 	}
 
-	switch (srso_cmd) {
-	case SRSO_CMD_MICROCODE:
-		if (has_microcode) {
-			srso_mitigation = SRSO_MITIGATION_MICROCODE;
-			pr_warn(SRSO_NOTICE);
-		}
+	switch (srso_mitigation) {
+	case SRSO_MITIGATION_MICROCODE:
+		pr_warn(SRSO_NOTICE);
+		break;
+
+	case SRSO_MITIGATION_SAFE_RET:
+	case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
+		if (!IS_ENABLED(CONFIG_MITIGATION_SRSO))
+			pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
 		break;
 
-	case SRSO_CMD_SAFE_RET:
-		if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
+	case SRSO_MITIGATION_IBPB:
+		if (!IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY))
+			pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
+		break;
+
+	case SRSO_MITIGATION_IBPB_ON_VMEXIT:
+		if (!IS_ENABLED(CONFIG_MITIGATION_SRSO))
+			pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
+		break;
+	default:
+		break;
+	}
+}
+
+static void __init srso_update_mitigation(void)
+{
+	/* If retbleed is using IBPB, that works for SRSO as well */
+	if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB)
+		srso_mitigation = SRSO_MITIGATION_IBPB;
+
+	pr_info("%s\n", srso_strings[srso_mitigation]);
+}
+
+static void __init srso_apply_mitigation(void)
+{
+	if (!boot_cpu_has_bug(X86_BUG_SRSO) ||
+	     srso_mitigation == SRSO_MITIGATION_NONE) {
+		if (boot_cpu_has(X86_FEATURE_SBPB))
+			x86_pred_cmd = PRED_CMD_SBPB;
+		return;
+	}
+	switch (srso_mitigation) {
+	case SRSO_MITIGATION_SAFE_RET:
+	case SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED:
 			/*
 			 * Enable the return thunk for generated code
 			 * like ftrace, static_call, etc.
@@ -2750,42 +2775,17 @@ static void __init srso_select_mitigation(void)
 				setup_force_cpu_cap(X86_FEATURE_SRSO);
 				x86_return_thunk = srso_return_thunk;
 			}
-			if (has_microcode)
-				srso_mitigation = SRSO_MITIGATION_SAFE_RET;
-			else
-				srso_mitigation = SRSO_MITIGATION_SAFE_RET_UCODE_NEEDED;
-		} else {
-			pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
-		}
-		break;
-
-	case SRSO_CMD_IBPB:
-		if (IS_ENABLED(CONFIG_MITIGATION_IBPB_ENTRY)) {
-			if (has_microcode) {
-				setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
-				srso_mitigation = SRSO_MITIGATION_IBPB;
-			}
-		} else {
-			pr_err("WARNING: kernel not compiled with MITIGATION_IBPB_ENTRY.\n");
-		}
-		break;
-
-	case SRSO_CMD_IBPB_ON_VMEXIT:
-		if (IS_ENABLED(CONFIG_MITIGATION_SRSO)) {
-			if (!boot_cpu_has(X86_FEATURE_ENTRY_IBPB) && has_microcode) {
-				setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
-				srso_mitigation = SRSO_MITIGATION_IBPB_ON_VMEXIT;
-			}
-		} else {
-			pr_err("WARNING: kernel not compiled with MITIGATION_SRSO.\n");
-                }
 		break;
+	case SRSO_MITIGATION_IBPB:
+			setup_force_cpu_cap(X86_FEATURE_ENTRY_IBPB);
+			break;
+	case SRSO_MITIGATION_IBPB_ON_VMEXIT:
+			setup_force_cpu_cap(X86_FEATURE_IBPB_ON_VMEXIT);
+			break;
 	default:
-		break;
+			break;
 	}
 
-out:
-	pr_info("%s\n", srso_strings[srso_mitigation]);
 }
 
 #undef pr_fmt
-- 
2.34.1