x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS

Extend spectre_v2= boot option with Kernel IBRS.

  [jpoimboe: no STIBP with IBRS]
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>

Documentation/admin-guide/kernel-parameters.txt

@@ -5589,6 +5589,7 @@
 			eibrs		  - enhanced IBRS
 			eibrs,retpoline   - enhanced IBRS + Retpolines
 			eibrs,lfence      - enhanced IBRS + LFENCE
+			ibrs		  - use IBRS to protect kernel
 
 			Not specifying this option is equivalent to
 			spectre_v2=auto.

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

@@ -211,6 +211,7 @@ enum spectre_v2_mitigation {
 	SPECTRE_V2_EIBRS,
 	SPECTRE_V2_EIBRS_RETPOLINE,
 	SPECTRE_V2_EIBRS_LFENCE,
+	SPECTRE_V2_IBRS,
 };
 
 /* The indirect branch speculation control variants */

arch/x86/kernel/cpu/bugs.c

@@ -972,6 +972,7 @@ enum spectre_v2_mitigation_cmd {
 	SPECTRE_V2_CMD_EIBRS,
 	SPECTRE_V2_CMD_EIBRS_RETPOLINE,
 	SPECTRE_V2_CMD_EIBRS_LFENCE,
+	SPECTRE_V2_CMD_IBRS,
 };
 
 enum spectre_v2_user_cmd {
@@ -1044,11 +1045,12 @@ 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)
+static inline bool spectre_v2_in_ibrs_mode(enum spectre_v2_mitigation mode)
 {
-	return (mode == SPECTRE_V2_EIBRS ||
+	return mode == SPECTRE_V2_IBRS ||
+	       mode == SPECTRE_V2_EIBRS ||
 	       mode == SPECTRE_V2_EIBRS_RETPOLINE ||
-		mode == SPECTRE_V2_EIBRS_LFENCE);
+	       mode == SPECTRE_V2_EIBRS_LFENCE;
 }
 
 static void __init
@@ -1113,12 +1115,12 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
 	}
 
 	/*
-	 * If no STIBP, enhanced IBRS is enabled or SMT impossible, STIBP is not
-	 * required.
+	 * If no STIBP, IBRS or enhanced IBRS is enabled, or SMT impossible,
+	 * STIBP is not required.
 	 */
 	if (!boot_cpu_has(X86_FEATURE_STIBP) ||
 	    !smt_possible ||
-	    spectre_v2_in_eibrs_mode(spectre_v2_enabled))
+	    spectre_v2_in_ibrs_mode(spectre_v2_enabled))
 		return;
 
 	/*
@@ -1150,6 +1152,7 @@ static const char * const spectre_v2_strings[] = {
 	[SPECTRE_V2_EIBRS]			= "Mitigation: Enhanced IBRS",
 	[SPECTRE_V2_EIBRS_LFENCE]		= "Mitigation: Enhanced IBRS + LFENCE",
 	[SPECTRE_V2_EIBRS_RETPOLINE]		= "Mitigation: Enhanced IBRS + Retpolines",
+	[SPECTRE_V2_IBRS]			= "Mitigation: IBRS",
 };
 
 static const struct {
@@ -1167,6 +1170,7 @@ static const struct {
 	{ "eibrs,lfence",	SPECTRE_V2_CMD_EIBRS_LFENCE,	  false },
 	{ "eibrs,retpoline",	SPECTRE_V2_CMD_EIBRS_RETPOLINE,	  false },
 	{ "auto",		SPECTRE_V2_CMD_AUTO,		  false },
+	{ "ibrs",		SPECTRE_V2_CMD_IBRS,              false },
 };
 
 static void __init spec_v2_print_cond(const char *reason, bool secure)
@@ -1229,6 +1233,24 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 		return SPECTRE_V2_CMD_AUTO;
 	}
 
+	if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
+		pr_err("%s selected but not Intel CPU. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_IBRS && !boot_cpu_has(X86_FEATURE_IBRS)) {
+		pr_err("%s selected but CPU doesn't have IBRS. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
+	if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_has(X86_FEATURE_XENPV)) {
+		pr_err("%s selected but running as XenPV guest. Switching to AUTO select\n",
+		       mitigation_options[i].option);
+		return SPECTRE_V2_CMD_AUTO;
+	}
+
 	spec_v2_print_cond(mitigation_options[i].option,
 			   mitigation_options[i].secure);
 	return cmd;
@@ -1268,6 +1290,14 @@ static void __init spectre_v2_select_mitigation(void)
 			break;
 		}
 
+		if (boot_cpu_has_bug(X86_BUG_RETBLEED) &&
+		    retbleed_cmd != RETBLEED_CMD_OFF &&
+		    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;
 
@@ -1284,6 +1314,10 @@ static void __init spectre_v2_select_mitigation(void)
 		mode = spectre_v2_select_retpoline();
 		break;
 
+	case SPECTRE_V2_CMD_IBRS:
+		mode = SPECTRE_V2_IBRS;
+		break;
+
 	case SPECTRE_V2_CMD_EIBRS:
 		mode = SPECTRE_V2_EIBRS;
 		break;
@@ -1300,7 +1334,7 @@ static void __init spectre_v2_select_mitigation(void)
 	if (mode == SPECTRE_V2_EIBRS && unprivileged_ebpf_enabled())
 		pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);
 
-	if (spectre_v2_in_eibrs_mode(mode)) {
+	if (spectre_v2_in_ibrs_mode(mode)) {
 		/* Force it so VMEXIT will restore correctly */
 		x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
 		write_spec_ctrl_current(x86_spec_ctrl_base, true);
@@ -1311,6 +1345,10 @@ static void __init spectre_v2_select_mitigation(void)
 	case SPECTRE_V2_EIBRS:
 		break;
 
+	case SPECTRE_V2_IBRS:
+		setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS);
+		break;
+
 	case SPECTRE_V2_LFENCE:
 	case SPECTRE_V2_EIBRS_LFENCE:
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE_LFENCE);
@@ -1337,17 +1375,17 @@ static void __init spectre_v2_select_mitigation(void)
 	pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
 
 	/*
-	 * Retpoline means the kernel is safe because it has no indirect
-	 * branches. Enhanced IBRS protects firmware too, so, enable restricted
-	 * speculation around firmware calls only when Enhanced IBRS isn't
-	 * supported.
+	 * Retpoline protects the kernel, but doesn't protect firmware.  IBRS
+	 * and Enhanced IBRS protect firmware too, so enable IBRS around
+	 * firmware calls only when IBRS / Enhanced 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.
 	 */
-	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_eibrs_mode(mode)) {
+	if (boot_cpu_has(X86_FEATURE_IBRS) && !spectre_v2_in_ibrs_mode(mode)) {
 		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
 		pr_info("Enabling Restricted Speculation for firmware calls\n");
 	}
@@ -2089,7 +2127,7 @@ static ssize_t mmio_stale_data_show_state(char *buf)
 
 static char *stibp_state(void)
 {
-	if (spectre_v2_in_eibrs_mode(spectre_v2_enabled))
+	if (spectre_v2_in_ibrs_mode(spectre_v2_enabled))
 		return "";
 
 	switch (spectre_v2_user_stibp) {