1 files changed, 678 insertions, 37 deletions

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index af35052d06ed..d0846ba818ee 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -30,6 +30,7 @@
 #include <asm/facility.h>
 #include <asm/nospec-branch.h>
 #include <asm/set_memory.h>
+#include <asm/text-patching.h>
 #include "bpf_jit.h"
 
 struct bpf_jit {
@@ -50,12 +51,13 @@ struct bpf_jit {
 	int r14_thunk_ip;	/* Address of expoline thunk for 'br %r14' */
 	int tail_call_start;	/* Tail call start offset */
 	int excnt;		/* Number of exception table entries */
+	int prologue_plt_ret;	/* Return address for prologue hotpatch PLT */
+	int prologue_plt;	/* Start of prologue hotpatch PLT */
 };
 
 #define SEEN_MEM	BIT(0)		/* use mem[] for temporary storage */
 #define SEEN_LITERAL	BIT(1)		/* code uses literals */
 #define SEEN_FUNC	BIT(2)		/* calls C functions */
-#define SEEN_TAIL_CALL	BIT(3)		/* code uses tail calls */
 #define SEEN_STACK	(SEEN_FUNC | SEEN_MEM)
 
 /*
@@ -68,6 +70,10 @@ struct bpf_jit {
 #define REG_0		REG_W0			/* Register 0 */
 #define REG_1		REG_W1			/* Register 1 */
 #define REG_2		BPF_REG_1		/* Register 2 */
+#define REG_3		BPF_REG_2		/* Register 3 */
+#define REG_4		BPF_REG_3		/* Register 4 */
+#define REG_7		BPF_REG_6		/* Register 7 */
+#define REG_8		BPF_REG_7		/* Register 8 */
 #define REG_14		BPF_REG_0		/* Register 14 */
 
 /*
@@ -507,20 +513,58 @@ static void bpf_skip(struct bpf_jit *jit, int size)
 }
 
 /*
+ * PLT for hotpatchable calls. The calling convention is the same as for the
+ * ftrace hotpatch trampolines: %r0 is return address, %r1 is clobbered.
+ */
+extern const char bpf_plt[];
+extern const char bpf_plt_ret[];
+extern const char bpf_plt_target[];
+extern const char bpf_plt_end[];
+#define BPF_PLT_SIZE 32
+asm(
+	".pushsection .rodata\n"
+	"	.align 8\n"
+	"bpf_plt:\n"
+	"	lgrl %r0,bpf_plt_ret\n"
+	"	lgrl %r1,bpf_plt_target\n"
+	"	br %r1\n"
+	"	.align 8\n"
+	"bpf_plt_ret: .quad 0\n"
+	"bpf_plt_target: .quad 0\n"
+	"bpf_plt_end:\n"
+	"	.popsection\n"
+);
+
+static void bpf_jit_plt(void *plt, void *ret, void *target)
+{
+	memcpy(plt, bpf_plt, BPF_PLT_SIZE);
+	*(void **)((char *)plt + (bpf_plt_ret - bpf_plt)) = ret;
+	*(void **)((char *)plt + (bpf_plt_target - bpf_plt)) = target;
+}
+
+/*
  * Emit function prologue
  *
  * Save registers and create stack frame if necessary.
- * See stack frame layout desription in "bpf_jit.h"!
+ * See stack frame layout description in "bpf_jit.h"!
  */
-static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
+static void bpf_jit_prologue(struct bpf_jit *jit, struct bpf_prog *fp,
+			     u32 stack_depth)
 {
-	if (jit->seen & SEEN_TAIL_CALL) {
+	/* No-op for hotpatching */
+	/* brcl 0,prologue_plt */
+	EMIT6_PCREL_RILC(0xc0040000, 0, jit->prologue_plt);
+	jit->prologue_plt_ret = jit->prg;
+
+	if (fp->aux->func_idx == 0) {
+		/* Initialize the tail call counter in the main program. */
 		/* xc STK_OFF_TCCNT(4,%r15),STK_OFF_TCCNT(%r15) */
 		_EMIT6(0xd703f000 | STK_OFF_TCCNT, 0xf000 | STK_OFF_TCCNT);
 	} else {
 		/*
-		 * There are no tail calls. Insert nops in order to have
-		 * tail_call_start at a predictable offset.
+		 * Skip the tail call counter initialization in subprograms.
+		 * Insert nops in order to have tail_call_start at a
+		 * predictable offset.
 		 */
 		bpf_skip(jit, 6);
 	}
@@ -558,6 +602,43 @@ static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
 }
 
 /*
+ * Emit an expoline for a jump that follows
+ */
+static void emit_expoline(struct bpf_jit *jit)
+{
+	/* exrl %r0,.+10 */
+	EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
+	/* j . */
+	EMIT4_PCREL(0xa7f40000, 0);
+}
+
+/*
+ * Emit __s390_indirect_jump_r1 thunk if necessary
+ */
+static void emit_r1_thunk(struct bpf_jit *jit)
+{
+	if (nospec_uses_trampoline()) {
+		jit->r1_thunk_ip = jit->prg;
+		emit_expoline(jit);
+		/* br %r1 */
+		_EMIT2(0x07f1);
+	}
+}
+
+/*
+ * Call r1 either directly or via __s390_indirect_jump_r1 thunk
+ */
+static void call_r1(struct bpf_jit *jit)
+{
+	if (nospec_uses_trampoline())
+		/* brasl %r14,__s390_indirect_jump_r1 */
+		EMIT6_PCREL_RILB(0xc0050000, REG_14, jit->r1_thunk_ip);
+	else
+		/* basr %r14,%r1 */
+		EMIT2(0x0d00, REG_14, REG_1);
+}
+
+/*
  * Function epilogue
  */
 static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth)
@@ -570,25 +651,20 @@ static void bpf_jit_epilogue(struct bpf_jit *jit, u32 stack_depth)
 	if (nospec_uses_trampoline()) {
 		jit->r14_thunk_ip = jit->prg;
 		/* Generate __s390_indirect_jump_r14 thunk */
-		/* exrl %r0,.+10 */
-		EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
-		/* j . */
-		EMIT4_PCREL(0xa7f40000, 0);
+		emit_expoline(jit);
 	}
 	/* br %r14 */
 	_EMIT2(0x07fe);
 
-	if ((nospec_uses_trampoline()) &&
-	    (is_first_pass(jit) || (jit->seen & SEEN_FUNC))) {
-		jit->r1_thunk_ip = jit->prg;
-		/* Generate __s390_indirect_jump_r1 thunk */
-		/* exrl %r0,.+10 */
-		EMIT6_PCREL_RIL(0xc6000000, jit->prg + 10);
-		/* j . */
-		EMIT4_PCREL(0xa7f40000, 0);
-		/* br %r1 */
-		_EMIT2(0x07f1);
-	}
+	if (is_first_pass(jit) || (jit->seen & SEEN_FUNC))
+		emit_r1_thunk(jit);
+
+	jit->prg = ALIGN(jit->prg, 8);
+	jit->prologue_plt = jit->prg;
+	if (jit->prg_buf)
+		bpf_jit_plt(jit->prg_buf + jit->prg,
+			    jit->prg_buf + jit->prologue_plt_ret, NULL);
+	jit->prg += BPF_PLT_SIZE;
 }
 
 static int get_probe_mem_regno(const u8 *insn)
@@ -663,6 +739,34 @@ static int bpf_jit_probe_mem(struct bpf_jit *jit, struct bpf_prog *fp,
 }
 
 /*
+ * Sign-extend the register if necessary
+ */
+static int sign_extend(struct bpf_jit *jit, int r, u8 size, u8 flags)
+{
+	if (!(flags & BTF_FMODEL_SIGNED_ARG))
+		return 0;
+
+	switch (size) {
+	case 1:
+		/* lgbr %r,%r */
+		EMIT4(0xb9060000, r, r);
+		return 0;
+	case 2:
+		/* lghr %r,%r */
+		EMIT4(0xb9070000, r, r);
+		return 0;
+	case 4:
+		/* lgfr %r,%r */
+		EMIT4(0xb9140000, r, r);
+		return 0;
+	case 8:
+		return 0;
+	default:
+		return -1;
+	}
+}
+
+/*
  * Compile one eBPF instruction into s390x code
  *
  * NOTE: Use noinline because for gcov (-fprofile-arcs) gcc allocates a lot of
@@ -1297,9 +1401,10 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 	 */
 	case BPF_JMP | BPF_CALL:
 	{
-		u64 func;
+		const struct btf_func_model *m;
 		bool func_addr_fixed;
-		int ret;
+		int j, ret;
+		u64 func;
 
 		ret = bpf_jit_get_func_addr(fp, insn, extra_pass,
 					    &func, &func_addr_fixed);
@@ -1308,15 +1413,38 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 
 		REG_SET_SEEN(BPF_REG_5);
 		jit->seen |= SEEN_FUNC;
+		/*
+		 * Copy the tail call counter to where the callee expects it.
+		 *
+		 * Note 1: The callee can increment the tail call counter, but
+		 * we do not load it back, since the x86 JIT does not do this
+		 * either.
+		 *
+		 * Note 2: We assume that the verifier does not let us call the
+		 * main program, which clears the tail call counter on entry.
+		 */
+		/* mvc STK_OFF_TCCNT(4,%r15),N(%r15) */
+		_EMIT6(0xd203f000 | STK_OFF_TCCNT,
+		       0xf000 | (STK_OFF_TCCNT + STK_OFF + stack_depth));
+
+		/* Sign-extend the kfunc arguments. */
+		if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
+			m = bpf_jit_find_kfunc_model(fp, insn);
+			if (!m)
+				return -1;
+
+			for (j = 0; j < m->nr_args; j++) {
+				if (sign_extend(jit, BPF_REG_1 + j,
+						m->arg_size[j],
+						m->arg_flags[j]))
+					return -1;
+			}
+		}
+
 		/* lgrl %w1,func */
 		EMIT6_PCREL_RILB(0xc4080000, REG_W1, _EMIT_CONST_U64(func));
-		if (nospec_uses_trampoline()) {
-			/* brasl %r14,__s390_indirect_jump_r1 */
-			EMIT6_PCREL_RILB(0xc0050000, REG_14, jit->r1_thunk_ip);
-		} else {
-			/* basr %r14,%w1 */
-			EMIT2(0x0d00, REG_14, REG_W1);
-		}
+		/* %r1() */
+		call_r1(jit);
 		/* lgr %b0,%r2: load return value into %b0 */
 		EMIT4(0xb9040000, BPF_REG_0, REG_2);
 		break;
@@ -1329,10 +1457,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		 *  B1: pointer to ctx
 		 *  B2: pointer to bpf_array
 		 *  B3: index in bpf_array
-		 */
-		jit->seen |= SEEN_TAIL_CALL;
-
-		/*
+		 *
 		 * if (index >= array->map.max_entries)
 		 *         goto out;
 		 */
@@ -1393,8 +1518,16 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
 		/* lg %r1,bpf_func(%r1) */
 		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, REG_1, REG_0,
 			      offsetof(struct bpf_prog, bpf_func));
-		/* bc 0xf,tail_call_start(%r1) */
-		_EMIT4(0x47f01000 + jit->tail_call_start);
+		if (nospec_uses_trampoline()) {
+			jit->seen |= SEEN_FUNC;
+			/* aghi %r1,tail_call_start */
+			EMIT4_IMM(0xa70b0000, REG_1, jit->tail_call_start);
+			/* brcl 0xf,__s390_indirect_jump_r1 */
+			EMIT6_PCREL_RILC(0xc0040000, 0xf, jit->r1_thunk_ip);
+		} else {
+			/* bc 0xf,tail_call_start(%r1) */
+			_EMIT4(0x47f01000 + jit->tail_call_start);
+		}
 		/* out: */
 		if (jit->prg_buf) {
 			*(u16 *)(jit->prg_buf + patch_1_clrj + 2) =
@@ -1688,7 +1821,7 @@ static int bpf_jit_prog(struct bpf_jit *jit, struct bpf_prog *fp,
 	jit->prg = 0;
 	jit->excnt = 0;
 
-	bpf_jit_prologue(jit, stack_depth);
+	bpf_jit_prologue(jit, fp, stack_depth);
 	if (bpf_set_addr(jit, 0) < 0)
 		return -1;
 	for (i = 0; i < fp->len; i += insn_count) {
@@ -1768,6 +1901,9 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	struct bpf_jit jit;
 	int pass;
 
+	if (WARN_ON_ONCE(bpf_plt_end - bpf_plt != BPF_PLT_SIZE))
+		return orig_fp;
+
 	if (!fp->jit_requested)
 		return orig_fp;
 
@@ -1859,3 +1995,508 @@ out:
 					   tmp : orig_fp);
 	return fp;
 }
+
+bool bpf_jit_supports_kfunc_call(void)
+{
+	return true;
+}
+
+int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
+		       void *old_addr, void *new_addr)
+{
+	struct {
+		u16 opc;
+		s32 disp;
+	} __packed insn;
+	char expected_plt[BPF_PLT_SIZE];
+	char current_plt[BPF_PLT_SIZE];
+	char *plt;
+	int err;
+
+	/* Verify the branch to be patched. */
+	err = copy_from_kernel_nofault(&insn, ip, sizeof(insn));
+	if (err < 0)
+		return err;
+	if (insn.opc != (0xc004 | (old_addr ? 0xf0 : 0)))
+		return -EINVAL;
+
+	if (t == BPF_MOD_JUMP &&
+	    insn.disp == ((char *)new_addr - (char *)ip) >> 1) {
+		/*
+		 * The branch already points to the destination,
+		 * there is no PLT.
+		 */
+	} else {
+		/* Verify the PLT. */
+		plt = (char *)ip + (insn.disp << 1);
+		err = copy_from_kernel_nofault(current_plt, plt, BPF_PLT_SIZE);
+		if (err < 0)
+			return err;
+		bpf_jit_plt(expected_plt, (char *)ip + 6, old_addr);
+		if (memcmp(current_plt, expected_plt, BPF_PLT_SIZE))
+			return -EINVAL;
+		/* Adjust the call address. */
+		s390_kernel_write(plt + (bpf_plt_target - bpf_plt),
+				  &new_addr, sizeof(void *));
+	}
+
+	/* Adjust the mask of the branch. */
+	insn.opc = 0xc004 | (new_addr ? 0xf0 : 0);
+	s390_kernel_write((char *)ip + 1, (char *)&insn.opc + 1, 1);
+
+	/* Make the new code visible to the other CPUs. */
+	text_poke_sync_lock();
+
+	return 0;
+}
+
+struct bpf_tramp_jit {
+	struct bpf_jit common;
+	int orig_stack_args_off;/* Offset of arguments placed on stack by the
+				 * func_addr's original caller
+				 */
+	int stack_size;		/* Trampoline stack size */
+	int stack_args_off;	/* Offset of stack arguments for calling
+				 * func_addr, has to be at the top
+				 */
+	int reg_args_off;	/* Offset of register arguments for calling
+				 * func_addr
+				 */
+	int ip_off;		/* For bpf_get_func_ip(), has to be at
+				 * (ctx - 16)
+				 */
+	int arg_cnt_off;	/* For bpf_get_func_arg_cnt(), has to be at
+				 * (ctx - 8)
+				 */
+	int bpf_args_off;	/* Offset of BPF_PROG context, which consists
+				 * of BPF arguments followed by return value
+				 */
+	int retval_off;		/* Offset of return value (see above) */
+	int r7_r8_off;		/* Offset of saved %r7 and %r8, which are used
+				 * for __bpf_prog_enter() return value and
+				 * func_addr respectively
+				 */
+	int r14_off;		/* Offset of saved %r14 */
+	int run_ctx_off;	/* Offset of struct bpf_tramp_run_ctx */
+	int do_fexit;		/* do_fexit: label */
+};
+
+static void load_imm64(struct bpf_jit *jit, int dst_reg, u64 val)
+{
+	/* llihf %dst_reg,val_hi */
+	EMIT6_IMM(0xc00e0000, dst_reg, (val >> 32));
+	/* oilf %rdst_reg,val_lo */
+	EMIT6_IMM(0xc00d0000, dst_reg, val);
+}
+
+static int invoke_bpf_prog(struct bpf_tramp_jit *tjit,
+			   const struct btf_func_model *m,
+			   struct bpf_tramp_link *tlink, bool save_ret)
+{
+	struct bpf_jit *jit = &tjit->common;
+	int cookie_off = tjit->run_ctx_off +
+			 offsetof(struct bpf_tramp_run_ctx, bpf_cookie);
+	struct bpf_prog *p = tlink->link.prog;
+	int patch;
+
+	/*
+	 * run_ctx.cookie = tlink->cookie;
+	 */
+
+	/* %r0 = tlink->cookie */
+	load_imm64(jit, REG_W0, tlink->cookie);
+	/* stg %r0,cookie_off(%r15) */
+	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_W0, REG_0, REG_15, cookie_off);
+
+	/*
+	 * if ((start = __bpf_prog_enter(p, &run_ctx)) == 0)
+	 *         goto skip;
+	 */
+
+	/* %r1 = __bpf_prog_enter */
+	load_imm64(jit, REG_1, (u64)bpf_trampoline_enter(p));
+	/* %r2 = p */
+	load_imm64(jit, REG_2, (u64)p);
+	/* la %r3,run_ctx_off(%r15) */
+	EMIT4_DISP(0x41000000, REG_3, REG_15, tjit->run_ctx_off);
+	/* %r1() */
+	call_r1(jit);
+	/* ltgr %r7,%r2 */
+	EMIT4(0xb9020000, REG_7, REG_2);
+	/* brcl 8,skip */
+	patch = jit->prg;
+	EMIT6_PCREL_RILC(0xc0040000, 8, 0);
+
+	/*
+	 * retval = bpf_func(args, p->insnsi);
+	 */
+
+	/* %r1 = p->bpf_func */
+	load_imm64(jit, REG_1, (u64)p->bpf_func);
+	/* la %r2,bpf_args_off(%r15) */
+	EMIT4_DISP(0x41000000, REG_2, REG_15, tjit->bpf_args_off);
+	/* %r3 = p->insnsi */
+	if (!p->jited)
+		load_imm64(jit, REG_3, (u64)p->insnsi);
+	/* %r1() */
+	call_r1(jit);
+	/* stg %r2,retval_off(%r15) */
+	if (save_ret) {
+		if (sign_extend(jit, REG_2, m->ret_size, m->ret_flags))
+			return -1;
+		EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15,
+			      tjit->retval_off);
+	}
+
+	/* skip: */
+	if (jit->prg_buf)
+		*(u32 *)&jit->prg_buf[patch + 2] = (jit->prg - patch) >> 1;
+
+	/*
+	 * __bpf_prog_exit(p, start, &run_ctx);
+	 */
+
+	/* %r1 = __bpf_prog_exit */
+	load_imm64(jit, REG_1, (u64)bpf_trampoline_exit(p));
+	/* %r2 = p */
+	load_imm64(jit, REG_2, (u64)p);
+	/* lgr %r3,%r7 */
+	EMIT4(0xb9040000, REG_3, REG_7);
+	/* la %r4,run_ctx_off(%r15) */
+	EMIT4_DISP(0x41000000, REG_4, REG_15, tjit->run_ctx_off);
+	/* %r1() */
+	call_r1(jit);
+
+	return 0;
+}
+
+static int alloc_stack(struct bpf_tramp_jit *tjit, size_t size)
+{
+	int stack_offset = tjit->stack_size;
+
+	tjit->stack_size += size;
+	return stack_offset;
+}
+
+/* ABI uses %r2 - %r6 for parameter passing. */
+#define MAX_NR_REG_ARGS 5
+
+/* The "L" field of the "mvc" instruction is 8 bits. */
+#define MAX_MVC_SIZE 256
+#define MAX_NR_STACK_ARGS (MAX_MVC_SIZE / sizeof(u64))
+
+/* -mfentry generates a 6-byte nop on s390x. */
+#define S390X_PATCH_SIZE 6
+
+static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im,
+					 struct bpf_tramp_jit *tjit,
+					 const struct btf_func_model *m,
+					 u32 flags,
+					 struct bpf_tramp_links *tlinks,
+					 void *func_addr)
+{
+	struct bpf_tramp_links *fmod_ret = &tlinks[BPF_TRAMP_MODIFY_RETURN];
+	struct bpf_tramp_links *fentry = &tlinks[BPF_TRAMP_FENTRY];
+	struct bpf_tramp_links *fexit = &tlinks[BPF_TRAMP_FEXIT];
+	int nr_bpf_args, nr_reg_args, nr_stack_args;
+	struct bpf_jit *jit = &tjit->common;
+	int arg, bpf_arg_off;
+	int i, j;
+
+	/* Support as many stack arguments as "mvc" instruction can handle. */
+	nr_reg_args = min_t(int, m->nr_args, MAX_NR_REG_ARGS);
+	nr_stack_args = m->nr_args - nr_reg_args;
+	if (nr_stack_args > MAX_NR_STACK_ARGS)
+		return -ENOTSUPP;
+
+	/* Return to %r14, since func_addr and %r0 are not available. */
+	if (!func_addr && !(flags & BPF_TRAMP_F_ORIG_STACK))
+		flags |= BPF_TRAMP_F_SKIP_FRAME;
+
+	/*
+	 * Compute how many arguments we need to pass to BPF programs.
+	 * BPF ABI mirrors that of x86_64: arguments that are 16 bytes or
+	 * smaller are packed into 1 or 2 registers; larger arguments are
+	 * passed via pointers.
+	 * In s390x ABI, arguments that are 8 bytes or smaller are packed into
+	 * a register; larger arguments are passed via pointers.
+	 * We need to deal with this difference.
+	 */
+	nr_bpf_args = 0;
+	for (i = 0; i < m->nr_args; i++) {
+		if (m->arg_size[i] <= 8)
+			nr_bpf_args += 1;
+		else if (m->arg_size[i] <= 16)
+			nr_bpf_args += 2;
+		else
+			return -ENOTSUPP;
+	}
+
+	/*
+	 * Calculate the stack layout.
+	 */
+
+	/* Reserve STACK_FRAME_OVERHEAD bytes for the callees. */
+	tjit->stack_size = STACK_FRAME_OVERHEAD;
+	tjit->stack_args_off = alloc_stack(tjit, nr_stack_args * sizeof(u64));
+	tjit->reg_args_off = alloc_stack(tjit, nr_reg_args * sizeof(u64));
+	tjit->ip_off = alloc_stack(tjit, sizeof(u64));
+	tjit->arg_cnt_off = alloc_stack(tjit, sizeof(u64));
+	tjit->bpf_args_off = alloc_stack(tjit, nr_bpf_args * sizeof(u64));
+	tjit->retval_off = alloc_stack(tjit, sizeof(u64));
+	tjit->r7_r8_off = alloc_stack(tjit, 2 * sizeof(u64));
+	tjit->r14_off = alloc_stack(tjit, sizeof(u64));
+	tjit->run_ctx_off = alloc_stack(tjit,
+					sizeof(struct bpf_tramp_run_ctx));
+	/* The caller has already reserved STACK_FRAME_OVERHEAD bytes. */
+	tjit->stack_size -= STACK_FRAME_OVERHEAD;
+	tjit->orig_stack_args_off = tjit->stack_size + STACK_FRAME_OVERHEAD;
+
+	/* aghi %r15,-stack_size */
+	EMIT4_IMM(0xa70b0000, REG_15, -tjit->stack_size);
+	/* stmg %r2,%rN,fwd_reg_args_off(%r15) */
+	if (nr_reg_args)
+		EMIT6_DISP_LH(0xeb000000, 0x0024, REG_2,
+			      REG_2 + (nr_reg_args - 1), REG_15,
+			      tjit->reg_args_off);
+	for (i = 0, j = 0; i < m->nr_args; i++) {
+		if (i < MAX_NR_REG_ARGS)
+			arg = REG_2 + i;
+		else
+			arg = tjit->orig_stack_args_off +
+			      (i - MAX_NR_REG_ARGS) * sizeof(u64);
+		bpf_arg_off = tjit->bpf_args_off + j * sizeof(u64);
+		if (m->arg_size[i] <= 8) {
+			if (i < MAX_NR_REG_ARGS)
+				/* stg %arg,bpf_arg_off(%r15) */
+				EMIT6_DISP_LH(0xe3000000, 0x0024, arg,
+					      REG_0, REG_15, bpf_arg_off);
+			else
+				/* mvc bpf_arg_off(8,%r15),arg(%r15) */
+				_EMIT6(0xd207f000 | bpf_arg_off,
+				       0xf000 | arg);
+			j += 1;
+		} else {
+			if (i < MAX_NR_REG_ARGS) {
+				/* mvc bpf_arg_off(16,%r15),0(%arg) */
+				_EMIT6(0xd20ff000 | bpf_arg_off,
+				       reg2hex[arg] << 12);
+			} else {
+				/* lg %r1,arg(%r15) */
+				EMIT6_DISP_LH(0xe3000000, 0x0004, REG_1, REG_0,
+					      REG_15, arg);
+				/* mvc bpf_arg_off(16,%r15),0(%r1) */
+				_EMIT6(0xd20ff000 | bpf_arg_off, 0x1000);
+			}
+			j += 2;
+		}
+	}
+	/* stmg %r7,%r8,r7_r8_off(%r15) */
+	EMIT6_DISP_LH(0xeb000000, 0x0024, REG_7, REG_8, REG_15,
+		      tjit->r7_r8_off);
+	/* stg %r14,r14_off(%r15) */
+	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_14, REG_0, REG_15, tjit->r14_off);
+
+	if (flags & BPF_TRAMP_F_ORIG_STACK) {
+		/*
+		 * The ftrace trampoline puts the return address (which is the
+		 * address of the original function + S390X_PATCH_SIZE) into
+		 * %r0; see ftrace_shared_hotpatch_trampoline_br and
+		 * ftrace_init_nop() for details.
+		 */
+
+		/* lgr %r8,%r0 */
+		EMIT4(0xb9040000, REG_8, REG_0);
+	} else {
+		/* %r8 = func_addr + S390X_PATCH_SIZE */
+		load_imm64(jit, REG_8, (u64)func_addr + S390X_PATCH_SIZE);
+	}
+
+	/*
+	 * ip = func_addr;
+	 * arg_cnt = m->nr_args;
+	 */
+
+	if (flags & BPF_TRAMP_F_IP_ARG) {
+		/* %r0 = func_addr */
+		load_imm64(jit, REG_0, (u64)func_addr);
+		/* stg %r0,ip_off(%r15) */
+		EMIT6_DISP_LH(0xe3000000, 0x0024, REG_0, REG_0, REG_15,
+			      tjit->ip_off);
+	}
+	/* lghi %r0,nr_bpf_args */
+	EMIT4_IMM(0xa7090000, REG_0, nr_bpf_args);
+	/* stg %r0,arg_cnt_off(%r15) */
+	EMIT6_DISP_LH(0xe3000000, 0x0024, REG_0, REG_0, REG_15,
+		      tjit->arg_cnt_off);
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		/*
+		 * __bpf_tramp_enter(im);
+		 */
+
+		/* %r1 = __bpf_tramp_enter */
+		load_imm64(jit, REG_1, (u64)__bpf_tramp_enter);
+		/* %r2 = im */
+		load_imm64(jit, REG_2, (u64)im);
+		/* %r1() */
+		call_r1(jit);
+	}
+
+	for (i = 0; i < fentry->nr_links; i++)
+		if (invoke_bpf_prog(tjit, m, fentry->links[i],
+				    flags & BPF_TRAMP_F_RET_FENTRY_RET))
+			return -EINVAL;
+
+	if (fmod_ret->nr_links) {
+		/*
+		 * retval = 0;
+		 */
+
+		/* xc retval_off(8,%r15),retval_off(%r15) */
+		_EMIT6(0xd707f000 | tjit->retval_off,
+		       0xf000 | tjit->retval_off);
+
+		for (i = 0; i < fmod_ret->nr_links; i++) {
+			if (invoke_bpf_prog(tjit, m, fmod_ret->links[i], true))
+				return -EINVAL;
+
+			/*
+			 * if (retval)
+			 *         goto do_fexit;
+			 */
+
+			/* ltg %r0,retval_off(%r15) */
+			EMIT6_DISP_LH(0xe3000000, 0x0002, REG_0, REG_0, REG_15,
+				      tjit->retval_off);
+			/* brcl 7,do_fexit */
+			EMIT6_PCREL_RILC(0xc0040000, 7, tjit->do_fexit);
+		}
+	}
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		/*
+		 * retval = func_addr(args);
+		 */
+
+		/* lmg %r2,%rN,reg_args_off(%r15) */
+		if (nr_reg_args)
+			EMIT6_DISP_LH(0xeb000000, 0x0004, REG_2,
+				      REG_2 + (nr_reg_args - 1), REG_15,
+				      tjit->reg_args_off);
+		/* mvc stack_args_off(N,%r15),orig_stack_args_off(%r15) */
+		if (nr_stack_args)
+			_EMIT6(0xd200f000 |
+				       (nr_stack_args * sizeof(u64) - 1) << 16 |
+				       tjit->stack_args_off,
+			       0xf000 | tjit->orig_stack_args_off);
+		/* lgr %r1,%r8 */
+		EMIT4(0xb9040000, REG_1, REG_8);
+		/* %r1() */
+		call_r1(jit);
+		/* stg %r2,retval_off(%r15) */
+		EMIT6_DISP_LH(0xe3000000, 0x0024, REG_2, REG_0, REG_15,
+			      tjit->retval_off);
+
+		im->ip_after_call = jit->prg_buf + jit->prg;
+
+		/*
+		 * The following nop will be patched by bpf_tramp_image_put().
+		 */
+
+		/* brcl 0,im->ip_epilogue */
+		EMIT6_PCREL_RILC(0xc0040000, 0, (u64)im->ip_epilogue);
+	}
+
+	/* do_fexit: */
+	tjit->do_fexit = jit->prg;
+	for (i = 0; i < fexit->nr_links; i++)
+		if (invoke_bpf_prog(tjit, m, fexit->links[i], false))
+			return -EINVAL;
+
+	if (flags & BPF_TRAMP_F_CALL_ORIG) {
+		im->ip_epilogue = jit->prg_buf + jit->prg;
+
+		/*
+		 * __bpf_tramp_exit(im);
+		 */
+
+		/* %r1 = __bpf_tramp_exit */
+		load_imm64(jit, REG_1, (u64)__bpf_tramp_exit);
+		/* %r2 = im */
+		load_imm64(jit, REG_2, (u64)im);
+		/* %r1() */
+		call_r1(jit);
+	}
+
+	/* lmg %r2,%rN,reg_args_off(%r15) */
+	if ((flags & BPF_TRAMP_F_RESTORE_REGS) && nr_reg_args)
+		EMIT6_DISP_LH(0xeb000000, 0x0004, REG_2,
+			      REG_2 + (nr_reg_args - 1), REG_15,
+			      tjit->reg_args_off);
+	/* lgr %r1,%r8 */
+	if (!(flags & BPF_TRAMP_F_SKIP_FRAME))
+		EMIT4(0xb9040000, REG_1, REG_8);
+	/* lmg %r7,%r8,r7_r8_off(%r15) */
+	EMIT6_DISP_LH(0xeb000000, 0x0004, REG_7, REG_8, REG_15,
+		      tjit->r7_r8_off);
+	/* lg %r14,r14_off(%r15) */
+	EMIT6_DISP_LH(0xe3000000, 0x0004, REG_14, REG_0, REG_15, tjit->r14_off);
+	/* lg %r2,retval_off(%r15) */
+	if (flags & (BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_RET_FENTRY_RET))
+		EMIT6_DISP_LH(0xe3000000, 0x0004, REG_2, REG_0, REG_15,
+			      tjit->retval_off);
+	/* aghi %r15,stack_size */
+	EMIT4_IMM(0xa70b0000, REG_15, tjit->stack_size);
+	/* Emit an expoline for the following indirect jump. */
+	if (nospec_uses_trampoline())
+		emit_expoline(jit);
+	if (flags & BPF_TRAMP_F_SKIP_FRAME)
+		/* br %r14 */
+		_EMIT2(0x07fe);
+	else
+		/* br %r1 */
+		_EMIT2(0x07f1);
+
+	emit_r1_thunk(jit);
+
+	return 0;
+}
+
+int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image,
+				void *image_end, const struct btf_func_model *m,
+				u32 flags, struct bpf_tramp_links *tlinks,
+				void *func_addr)
+{
+	struct bpf_tramp_jit tjit;
+	int ret;
+	int i;
+
+	for (i = 0; i < 2; i++) {
+		if (i == 0) {
+			/* Compute offsets, check whether the code fits. */
+			memset(&tjit, 0, sizeof(tjit));
+		} else {
+			/* Generate the code. */
+			tjit.common.prg = 0;
+			tjit.common.prg_buf = image;
+		}
+		ret = __arch_prepare_bpf_trampoline(im, &tjit, m, flags,
+						    tlinks, func_addr);
+		if (ret < 0)
+			return ret;
+		if (tjit.common.prg > (char *)image_end - (char *)image)
+			/*
+			 * Use the same error code as for exceeding
+			 * BPF_MAX_TRAMP_LINKS.
+			 */
+			return -E2BIG;
+	}
+
+	return ret;
+}
+
+bool bpf_jit_supports_subprog_tailcalls(void)
+{
+	return true;
+}