[PATCH v4 13/36] x86/bugs: Restructure spectre_v2 mitigation

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

Restructure spectre_v2 to use select/update/apply functions to create
consistent vulnerability handling.

The spectre_v2 mitigation may be updated based on the selected retbleed
mitigation.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
 arch/x86/kernel/cpu/bugs.c | 79 +++++++++++++++++++++++---------------
 1 file changed, 48 insertions(+), 31 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 96cb2ac70245..b4a72ddf159c 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -56,6 +56,8 @@
 static void __init spectre_v1_select_mitigation(void);
 static void __init spectre_v1_apply_mitigation(void);
 static void __init spectre_v2_select_mitigation(void);
+static void __init spectre_v2_update_mitigation(void);
+static void __init spectre_v2_apply_mitigation(void);
 static void __init retbleed_select_mitigation(void);
 static void __init retbleed_update_mitigation(void);
 static void __init retbleed_apply_mitigation(void);
@@ -212,7 +214,12 @@ void __init cpu_select_mitigations(void)
 	/*
 	 * After mitigations are selected, some may need to update their
 	 * choices.
+	 *
+	 * Note that retbleed_update_mitigation() relies on the state set by
+	 * spectre_v2_update_mitigation(); specifically it wants to know about
+	 * spectre_v2=ibrs.
 	 */
+	spectre_v2_update_mitigation();
 	retbleed_update_mitigation();
 	/* spectre_v2_user_update_mitigation() depends on retbleed_mitigation */
 	spectre_v2_user_update_mitigation();
@@ -222,6 +229,7 @@ void __init cpu_select_mitigations(void)
 	rfds_update_mitigation();
 
 	spectre_v1_apply_mitigation();
+	spectre_v2_apply_mitigation();
 	retbleed_apply_mitigation();
 	spectre_v2_user_apply_mitigation();
 	mds_apply_mitigation();
@@ -1847,18 +1855,18 @@ static void __init bhi_apply_mitigation(void)
 
 static void __init spectre_v2_select_mitigation(void)
 {
-	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
 	enum spectre_v2_mitigation mode = SPECTRE_V2_NONE;
+	spectre_v2_cmd = spectre_v2_parse_cmdline();
 
 	/*
 	 * If the CPU is not affected and the command line mode is NONE or AUTO
 	 * then nothing to do.
 	 */
 	if (!boot_cpu_has_bug(X86_BUG_SPECTRE_V2) &&
-	    (cmd == SPECTRE_V2_CMD_NONE || cmd == SPECTRE_V2_CMD_AUTO))
+	    (spectre_v2_cmd == SPECTRE_V2_CMD_NONE || spectre_v2_cmd == SPECTRE_V2_CMD_AUTO))
 		return;
 
-	switch (cmd) {
+	switch (spectre_v2_cmd) {
 	case SPECTRE_V2_CMD_NONE:
 		return;
 
@@ -1869,16 +1877,6 @@ static void __init spectre_v2_select_mitigation(void)
 			break;
 		}
 
-		if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) &&
-		    boot_cpu_has_bug(X86_BUG_RETBLEED) &&
-		    retbleed_mitigation != RETBLEED_MITIGATION_NONE &&
-		    retbleed_mitigation != RETBLEED_MITIGATION_STUFF &&
-		    boot_cpu_has(X86_FEATURE_IBRS) &&
-		    boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
-			mode = SPECTRE_V2_IBRS;
-			break;
-		}
-
 		mode = spectre_v2_select_retpoline();
 		break;
 
@@ -1912,10 +1910,32 @@ static void __init spectre_v2_select_mitigation(void)
 		break;
 	}
 
-	if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
+	spectre_v2_enabled = mode;
+}
+
+static void __init spectre_v2_update_mitigation(void)
+{
+	if (spectre_v2_cmd == SPECTRE_V2_CMD_AUTO) {
+		if (IS_ENABLED(CONFIG_MITIGATION_IBRS_ENTRY) &&
+		    boot_cpu_has_bug(X86_BUG_RETBLEED) &&
+		    retbleed_mitigation != RETBLEED_MITIGATION_NONE &&
+		    retbleed_mitigation != RETBLEED_MITIGATION_STUFF &&
+		    boot_cpu_has(X86_FEATURE_IBRS) &&
+		    boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+			spectre_v2_enabled = SPECTRE_V2_IBRS;
+		}
+	}
+
+	if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) && !cpu_mitigations_off())
+		pr_info("%s\n", spectre_v2_strings[spectre_v2_enabled]);
+}
+
+static void __init spectre_v2_apply_mitigation(void)
+{
+	if (spectre_v2_enabled == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
 		pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);
 
-	if (spectre_v2_in_ibrs_mode(mode)) {
+	if (spectre_v2_in_ibrs_mode(spectre_v2_enabled)) {
 		if (boot_cpu_has(X86_FEATURE_AUTOIBRS)) {
 			msr_set_bit(MSR_EFER, _EFER_AUTOIBRS);
 		} else {
@@ -1924,8 +1944,10 @@ static void __init spectre_v2_select_mitigation(void)
 		}
 	}
 
-	switch (mode) {
+	switch (spectre_v2_enabled) {
 	case SPECTRE_V2_NONE:
+		return;
+
 	case SPECTRE_V2_EIBRS:
 		break;
 
@@ -1951,14 +1973,11 @@ static void __init spectre_v2_select_mitigation(void)
 	 * JMPs gets protection against BHI and Intramode-BTI, but RET
 	 * prediction from a non-RSB predictor is still a risk.
 	 */
-	if (mode == SPECTRE_V2_EIBRS_LFENCE ||
-	    mode == SPECTRE_V2_EIBRS_RETPOLINE ||
-	    mode == SPECTRE_V2_RETPOLINE)
+	if (spectre_v2_enabled == SPECTRE_V2_EIBRS_LFENCE ||
+	    spectre_v2_enabled == SPECTRE_V2_EIBRS_RETPOLINE ||
+	    spectre_v2_enabled == SPECTRE_V2_RETPOLINE)
 		spec_ctrl_disable_kernel_rrsba();
 
-	spectre_v2_enabled = mode;
-	pr_info("%s\n", spectre_v2_strings[mode]);
-
 	/*
 	 * If Spectre v2 protection has been enabled, fill the RSB during a
 	 * context switch.  In general there are two types of RSB attacks
@@ -2000,7 +2019,7 @@ static void __init spectre_v2_select_mitigation(void)
 	setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
 	pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
 
-	spectre_v2_determine_rsb_fill_type_at_vmexit(mode);
+	spectre_v2_determine_rsb_fill_type_at_vmexit(spectre_v2_enabled);
 
 	/*
 	 * Retpoline protects the kernel, but doesn't protect firmware.  IBRS
@@ -2008,10 +2027,10 @@ static void __init spectre_v2_select_mitigation(void)
 	 * firmware calls only when IBRS / Enhanced / Automatic IBRS aren't
 	 * otherwise enabled.
 	 *
-	 * Use "mode" to check Enhanced IBRS instead of boot_cpu_has(), because
-	 * the user might select retpoline on the kernel command line and if
-	 * the CPU supports Enhanced IBRS, kernel might un-intentionally not
-	 * enable IBRS around firmware calls.
+	 * Use "spectre_v2_enabled" to check Enhanced IBRS instead of
+	 * boot_cpu_has(), because the user might select retpoline on the kernel
+	 * command line and if the CPU supports Enhanced IBRS, kernel might
+	 * un-intentionally not enable IBRS around firmware calls.
 	 */
 	if (boot_cpu_has_bug(X86_BUG_RETBLEED) &&
 	    boot_cpu_has(X86_FEATURE_IBPB) &&
@@ -2023,13 +2042,11 @@ static void __init spectre_v2_select_mitigation(void)
 			pr_info("Enabling Speculation Barrier for firmware calls\n");
 		}
 
-	} else if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
+	} else if (boot_cpu_has(X86_FEATURE_IBRS) &&
+		   !spectre_v2_in_ibrs_mode(spectre_v2_enabled)) {
 		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
 		pr_info("Enabling Restricted Speculation for firmware calls\n");
 	}
-
-	/* Set up IBPB and STIBP depending on the general spectre V2 command */
-	spectre_v2_cmd = cmd;
 }
 
 static void update_stibp_msr(void * __unused)
-- 
2.34.1