x86/speculation: Add eIBRS + Retpoline options

Thanks to the chaps at VUsec it is now clear that eIBRS is not
sufficient, therefore allow enabling of retpolines along with eIBRS.

Add spectre_v2=eibrs, spectre_v2=eibrs,lfence and
spectre_v2=eibrs,retpoline options to explicitly pick your preferred
means of mitigation.

Since there's new mitigations there's also user visible changes in
/sys/devices/system/cpu/vulnerabilities/spectre_v2 to reflect these
new mitigations.

  [ bp: Massage commit message, trim error messages,
    do more precise eIBRS mode checking. ]
Co-developed-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NBorislav Petkov <bp@suse.de>
Reviewed-by: NPatrick Colp <patrick.colp@oracle.com>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/nospec-branch.h

@@ -190,7 +190,9 @@ enum spectre_v2_mitigation {
 	SPECTRE_V2_NONE,
 	SPECTRE_V2_RETPOLINE,
 	SPECTRE_V2_LFENCE,
-	SPECTRE_V2_IBRS_ENHANCED,
+	SPECTRE_V2_EIBRS,
+	SPECTRE_V2_EIBRS_RETPOLINE,
+	SPECTRE_V2_EIBRS_LFENCE,
 };
 
 /* The indirect branch speculation control variants */

arch/x86/kernel/cpu/bugs.c

@@ -665,6 +665,9 @@ enum spectre_v2_mitigation_cmd {
 	SPECTRE_V2_CMD_RETPOLINE,
 	SPECTRE_V2_CMD_RETPOLINE_GENERIC,
 	SPECTRE_V2_CMD_RETPOLINE_LFENCE,
+	SPECTRE_V2_CMD_EIBRS,
+	SPECTRE_V2_CMD_EIBRS_RETPOLINE,
+	SPECTRE_V2_CMD_EIBRS_LFENCE,
 };
 
 enum spectre_v2_user_cmd {
@@ -737,6 +740,13 @@ spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
 	return SPECTRE_V2_USER_CMD_AUTO;
 }
 
+static inline bool spectre_v2_in_eibrs_mode(enum spectre_v2_mitigation mode)
+{
+	return (mode == SPECTRE_V2_EIBRS ||
+		mode == SPECTRE_V2_EIBRS_RETPOLINE ||
+		mode == SPECTRE_V2_EIBRS_LFENCE);
+}
+
 static void __init
 spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 {
@@ -804,7 +814,7 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 	 */
 	if (!boot_cpu_has(X86_FEATURE_STIBP) ||
 	    !smt_possible ||
-	    spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+	    spectre_v2_in_eibrs_mode(spectre_v2_enabled))
 		return;
 
 	/*
@@ -826,7 +836,9 @@ static const char * const spectre_v2_strings[] = {
 	[SPECTRE_V2_NONE]			= "Vulnerable",
 	[SPECTRE_V2_RETPOLINE]			= "Mitigation: Retpolines",
 	[SPECTRE_V2_LFENCE]			= "Mitigation: LFENCE",
-	[SPECTRE_V2_IBRS_ENHANCED]		= "Mitigation: Enhanced IBRS",
+	[SPECTRE_V2_EIBRS]			= "Mitigation: Enhanced IBRS",
+	[SPECTRE_V2_EIBRS_LFENCE]		= "Mitigation: Enhanced IBRS + LFENCE",
+	[SPECTRE_V2_EIBRS_RETPOLINE]		= "Mitigation: Enhanced IBRS + Retpolines",
 };
 
 static const struct {
@@ -840,6 +852,9 @@ static const struct {
 	{ "retpoline,amd",	SPECTRE_V2_CMD_RETPOLINE_LFENCE,  false },
 	{ "retpoline,lfence",	SPECTRE_V2_CMD_RETPOLINE_LFENCE,  false },
 	{ "retpoline,generic",	SPECTRE_V2_CMD_RETPOLINE_GENERIC, false },
+	{ "eibrs",		SPECTRE_V2_CMD_EIBRS,		  false },
+	{ "eibrs,lfence",	SPECTRE_V2_CMD_EIBRS_LFENCE,	  false },
+	{ "eibrs,retpoline",	SPECTRE_V2_CMD_EIBRS_RETPOLINE,	  false },
 	{ "auto",		SPECTRE_V2_CMD_AUTO,		  false },
 };
 
@@ -877,15 +892,29 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 
 	if ((cmd == SPECTRE_V2_CMD_RETPOLINE ||
 	     cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
-	     cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC) &&
+	     cmd == SPECTRE_V2_CMD_RETPOLINE_GENERIC ||
+	     cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
+	     cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
 	    !IS_ENABLED(CONFIG_RETPOLINE)) {
-		pr_err("%s selected but not compiled in. Switching to AUTO select\n", mitigation_options[i].option);
+		pr_err("%s selected but not compiled in. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if ((cmd == SPECTRE_V2_CMD_EIBRS ||
+	     cmd == SPECTRE_V2_CMD_EIBRS_LFENCE ||
+	     cmd == SPECTRE_V2_CMD_EIBRS_RETPOLINE) &&
+	    !boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
+		pr_err("%s selected but CPU doesn't have eIBRS. Switching to AUTO select\n",
+		       mitigation_options[i].option);
 		return SPECTRE_V2_CMD_AUTO;
 	}
 
-	if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE) &&
+	if ((cmd == SPECTRE_V2_CMD_RETPOLINE_LFENCE ||
+	     cmd == SPECTRE_V2_CMD_EIBRS_LFENCE) &&
 	    !boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
-		pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n", mitigation_options[i].option);
+		pr_err("%s selected, but CPU doesn't have a serializing LFENCE. Switching to AUTO select\n",
+		       mitigation_options[i].option);
 		return SPECTRE_V2_CMD_AUTO;
 	}
 
@@ -894,6 +923,25 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 	return cmd;
 }
 
+static enum spectre_v2_mitigation __init spectre_v2_select_retpoline(void)
+{
+	if (!IS_ENABLED(CONFIG_RETPOLINE)) {
+		pr_err("Kernel not compiled with retpoline; no mitigation available!");
+		return SPECTRE_V2_NONE;
+	}
+
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
+		if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
+			pr_err("LFENCE not serializing, switching to generic retpoline\n");
+			return SPECTRE_V2_RETPOLINE;
+		}
+		return SPECTRE_V2_LFENCE;
+	}
+
+	return SPECTRE_V2_RETPOLINE;
+}
+
 static void __init spectre_v2_select_mitigation(void)
 {
 	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@@ -914,49 +962,60 @@ static void __init spectre_v2_select_mitigation(void)
 	case SPECTRE_V2_CMD_FORCE:
 	case SPECTRE_V2_CMD_AUTO:
 		if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) {
-			mode = SPECTRE_V2_IBRS_ENHANCED;
-			/* Force it so VMEXIT will restore correctly */
-			x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
-			wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
-			goto specv2_set_mode;
+			mode = SPECTRE_V2_EIBRS;
+			break;
 		}
-		if (IS_ENABLED(CONFIG_RETPOLINE))
-			goto retpoline_auto;
+
+		mode = spectre_v2_select_retpoline();
 		break;
+
 	case SPECTRE_V2_CMD_RETPOLINE_LFENCE:
-		if (IS_ENABLED(CONFIG_RETPOLINE))
-			goto retpoline_lfence;
+		mode = SPECTRE_V2_LFENCE;
 		break;
+
 	case SPECTRE_V2_CMD_RETPOLINE_GENERIC:
-		if (IS_ENABLED(CONFIG_RETPOLINE))
-			goto retpoline_generic;
+		mode = SPECTRE_V2_RETPOLINE;
 		break;
+
 	case SPECTRE_V2_CMD_RETPOLINE:
-		if (IS_ENABLED(CONFIG_RETPOLINE))
-			goto retpoline_auto;
+		mode = spectre_v2_select_retpoline();
+		break;
+
+	case SPECTRE_V2_CMD_EIBRS:
+		mode = SPECTRE_V2_EIBRS;
+		break;
+
+	case SPECTRE_V2_CMD_EIBRS_LFENCE:
+		mode = SPECTRE_V2_EIBRS_LFENCE;
+		break;
+
+	case SPECTRE_V2_CMD_EIBRS_RETPOLINE:
+		mode = SPECTRE_V2_EIBRS_RETPOLINE;
 		break;
 	}
-	pr_err("Spectre mitigation: kernel not compiled with retpoline; no mitigation available!");
-	return;
 
-retpoline_auto:
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
-	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
-	retpoline_lfence:
-		if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
-			pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n");
-			goto retpoline_generic;
-		}
-		mode = SPECTRE_V2_LFENCE;
+	if (spectre_v2_in_eibrs_mode(mode)) {
+		/* Force it so VMEXIT will restore correctly */
+		x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
+		wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
+	}
+
+	switch (mode) {
+	case SPECTRE_V2_NONE:
+	case SPECTRE_V2_EIBRS:
+		break;
+
+	case SPECTRE_V2_LFENCE:
+	case SPECTRE_V2_EIBRS_LFENCE:
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE);
+		fallthrough;
+
+	case SPECTRE_V2_RETPOLINE:
+	case SPECTRE_V2_EIBRS_RETPOLINE:
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
-	} else {
-	retpoline_generic:
-		mode = SPECTRE_V2_RETPOLINE;
-		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
+		break;
 	}
 
-specv2_set_mode:
 	spectre_v2_enabled = mode;
 	pr_info("%s\n", spectre_v2_strings[mode]);
 
@@ -982,7 +1041,7 @@ static void __init spectre_v2_select_mitigation(void)
 	 * the CPU supports Enhanced IBRS, kernel might un-intentionally not
 	 * enable IBRS around firmware calls.
 	 */
-	if (boot_cpu_has(X86_FEATURE_IBRS) && mode != SPECTRE_V2_IBRS_ENHANCED) {
+	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_eibrs_mode(mode)) {
 		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
 		pr_info("Enabling Restricted Speculation for firmware calls\n");
 	}
@@ -1691,7 +1750,7 @@ static ssize_t tsx_async_abort_show_state(char *buf)
 
 static char *stibp_state(void)
 {
-	if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+	if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
 		return "";
 
 	switch (spectre_v2_user_stibp) {