1 files changed, 94 insertions, 29 deletions

diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
index 9aff72d3abda..18ae7b9c71d6 100644
--- a/arch/s390/kernel/nospec-branch.c
+++ b/arch/s390/kernel/nospec-branch.c
@@ -1,32 +1,86 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/module.h>
+#include <linux/device.h>
 #include <asm/nospec-branch.h>
 
-int nospec_call_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
-int nospec_return_disable = !IS_ENABLED(CONFIG_EXPOLINE_FULL);
+static int __init nobp_setup_early(char *str)
+{
+	bool enabled;
+	int rc;
+
+	rc = kstrtobool(str, &enabled);
+	if (rc)
+		return rc;
+	if (enabled && test_facility(82)) {
+		/*
+		 * The user explicitely requested nobp=1, enable it and
+		 * disable the expoline support.
+		 */
+		__set_facility(82, S390_lowcore.alt_stfle_fac_list);
+		if (IS_ENABLED(CONFIG_EXPOLINE))
+			nospec_disable = 1;
+	} else {
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
+	}
+	return 0;
+}
+early_param("nobp", nobp_setup_early);
+
+static int __init nospec_setup_early(char *str)
+{
+	__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
+	return 0;
+}
+early_param("nospec", nospec_setup_early);
+
+static int __init nospec_report(void)
+{
+	if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
+		pr_info("Spectre V2 mitigation: execute trampolines\n");
+	if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
+		pr_info("Spectre V2 mitigation: limited branch prediction\n");
+	return 0;
+}
+arch_initcall(nospec_report);
+
+#ifdef CONFIG_EXPOLINE
+
+int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
 
 static int __init nospectre_v2_setup_early(char *str)
 {
-	nospec_call_disable = 1;
-	nospec_return_disable = 1;
+	nospec_disable = 1;
 	return 0;
 }
 early_param("nospectre_v2", nospectre_v2_setup_early);
 
+void __init nospec_auto_detect(void)
+{
+	if (IS_ENABLED(CC_USING_EXPOLINE)) {
+		/*
+		 * The kernel has been compiled with expolines.
+		 * Keep expolines enabled and disable nobp.
+		 */
+		nospec_disable = 0;
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
+	}
+	/*
+	 * If the kernel has not been compiled with expolines the
+	 * nobp setting decides what is done, this depends on the
+	 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
+	 */
+}
+
 static int __init spectre_v2_setup_early(char *str)
 {
 	if (str && !strncmp(str, "on", 2)) {
-		nospec_call_disable = 0;
-		nospec_return_disable = 0;
-	}
-	if (str && !strncmp(str, "off", 3)) {
-		nospec_call_disable = 1;
-		nospec_return_disable = 1;
-	}
-	if (str && !strncmp(str, "auto", 4)) {
-		nospec_call_disable = 0;
-		nospec_return_disable = 1;
+		nospec_disable = 0;
+		__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
 	}
+	if (str && !strncmp(str, "off", 3))
+		nospec_disable = 1;
+	if (str && !strncmp(str, "auto", 4))
+		nospec_auto_detect();
 	return 0;
 }
 early_param("spectre_v2", spectre_v2_setup_early);
@@ -39,7 +93,6 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 	s32 *epo;
 
 	/* Second part of the instruction replace is always a nop */
-	memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4);
 	for (epo = start; epo < end; epo++) {
 		instr = (u8 *) epo + *epo;
 		if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
@@ -60,18 +113,34 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 			br = thunk + (*(int *)(thunk + 2)) * 2;
 		else
 			continue;
-		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
+		/* Check for unconditional branch 0x07f? or 0x47f???? */
+		if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
 			continue;
+
+		memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
 		switch (type) {
 		case BRCL_EXPOLINE:
-			/* brcl to thunk, replace with br + nop */
 			insnbuf[0] = br[0];
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			if (br[0] == 0x47) {
+				/* brcl to b, replace with bc + nopr */
+				insnbuf[2] = br[2];
+				insnbuf[3] = br[3];
+			} else {
+				/* brcl to br, replace with bcr + nop */
+			}
 			break;
 		case BRASL_EXPOLINE:
-			/* brasl to thunk, replace with basr + nop */
-			insnbuf[0] = 0x0d;
 			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			if (br[0] == 0x47) {
+				/* brasl to b, replace with bas + nopr */
+				insnbuf[0] = 0x4d;
+				insnbuf[2] = br[2];
+				insnbuf[3] = br[3];
+			} else {
+				/* brasl to br, replace with basr + nop */
+				insnbuf[0] = 0x0d;
+			}
 			break;
 		}
 
@@ -79,15 +148,9 @@ static void __init_or_module __nospec_revert(s32 *start, s32 *end)
 	}
 }
 
-void __init_or_module nospec_call_revert(s32 *start, s32 *end)
-{
-	if (nospec_call_disable)
-		__nospec_revert(start, end);
-}
-
-void __init_or_module nospec_return_revert(s32 *start, s32 *end)
+void __init_or_module nospec_revert(s32 *start, s32 *end)
 {
-	if (nospec_return_disable)
+	if (nospec_disable)
 		__nospec_revert(start, end);
 }
 
@@ -95,6 +158,8 @@ extern s32 __nospec_call_start[], __nospec_call_end[];
 extern s32 __nospec_return_start[], __nospec_return_end[];
 void __init nospec_init_branches(void)
 {
-	nospec_call_revert(__nospec_call_start, __nospec_call_end);
-	nospec_return_revert(__nospec_return_start, __nospec_return_end);
+	nospec_revert(__nospec_call_start, __nospec_call_end);
+	nospec_revert(__nospec_return_start, __nospec_return_end);
 }
+
+#endif /* CONFIG_EXPOLINE */