1 files changed, 100 insertions, 0 deletions
diff --git a/arch/s390/kernel/nospec-branch.c b/arch/s390/kernel/nospec-branch.c
new file mode 100644
index 000000000000..69d7fcf48158
--- /dev/null
+++ b/arch/s390/kernel/nospec-branch.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/module.h>
+#include <asm/nospec-branch.h>
+
+int nospec_call_disable = IS_ENABLED(EXPOLINE_OFF);
+int nospec_return_disable = !IS_ENABLED(EXPOLINE_FULL);
+
+static int __init nospectre_v2_setup_early(char *str)
+{
+	nospec_call_disable = 1;
+	nospec_return_disable = 1;
+	return 0;
+}
+early_param("nospectre_v2", nospectre_v2_setup_early);
+
+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;
+	}
+	return 0;
+}
+early_param("spectre_v2", spectre_v2_setup_early);
+
+static void __init_or_module __nospec_revert(s32 *start, s32 *end)
+{
+	enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
+	u8 *instr, *thunk, *br;
+	u8 insnbuf[6];
+	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)
+			type = BRCL_EXPOLINE;	/* brcl instruction */
+		else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
+			type = BRASL_EXPOLINE;	/* brasl instruction */
+		else
+			continue;
+		thunk = instr + (*(int *)(instr + 2)) * 2;
+		if (thunk[0] == 0xc6 && thunk[1] == 0x00)
+			/* exrl %r0,<target-br> */
+			br = thunk + (*(int *)(thunk + 2)) * 2;
+		else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
+			 thunk[6] == 0x44 && thunk[7] == 0x00 &&
+			 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
+			 (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
+			/* larl %rx,<target br> + ex %r0,0(%rx) */
+			br = thunk + (*(int *)(thunk + 2)) * 2;
+		else
+			continue;
+		if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
+			continue;
+		switch (type) {
+		case BRCL_EXPOLINE:
+			/* brcl to thunk, replace with br + nop */
+			insnbuf[0] = br[0];
+			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			break;
+		case BRASL_EXPOLINE:
+			/* brasl to thunk, replace with basr + nop */
+			insnbuf[0] = 0x0d;
+			insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
+			break;
+		}
+
+		s390_kernel_write(instr, insnbuf, 6);
+	}
+}
+
+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)
+{
+	if (nospec_return_disable)
+		__nospec_revert(start, end);
+}
+
+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);
+}