[PATCH bpf v2 2/6] bpf: powerpc64: add JIT support for multi-function programs

[Sandipan Das]

This adds support for bpf-to-bpf function calls in the powerpc64
JIT compiler. The JIT compiler converts the bpf call instructions
to native branch instructions. After a round of the usual passes,
the start addresses of the JITed images for the callee functions
are known. Finally, to fixup the branch target addresses, we need
to perform an extra pass.

Because of the address range in which JITed images are allocated
on powerpc64, the offsets of the start addresses of these images
from __bpf_call_base are as large as 64 bits. So, for a function
call, we cannot use the imm field of the instruction to determine
the callee's address. Instead, we use the alternative method of
getting it from the list of function addresses in the auxillary
data of the caller by using the off field as an index.

Signed-off-by: Sandipan Das <sandipan at linux.vnet.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp64.c | 79 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 69 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 1bdb1aff0619..25939892d8f7 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -256,7 +256,7 @@ static void bpf_jit_emit_tail_call(u32 *image, struct codegen_context *ctx, u32
 /* Assemble the body code between the prologue & epilogue */
 static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 			      struct codegen_context *ctx,
-			      u32 *addrs)
+			      u32 *addrs, bool extra_pass)
 {
 	const struct bpf_insn *insn = fp->insnsi;
 	int flen = fp->len;
@@ -712,11 +712,23 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 			break;
 
 		/*
-		 * Call kernel helper
+		 * Call kernel helper or bpf function
 		 */
 		case BPF_JMP | BPF_CALL:
 			ctx->seen |= SEEN_FUNC;
-			func = (u8 *) __bpf_call_base + imm;
+
+			/* bpf function call */
+			if (insn[i].src_reg == BPF_PSEUDO_CALL && extra_pass)
+				if (fp->aux->func && off < fp->aux->func_cnt)
+					/* use the subprog id from the off
+					 * field to lookup the callee address
+					 */
+					func = (u8 *) fp->aux->func[off]->bpf_func;
+				else
+					return -EINVAL;
+			/* kernel helper call */
+			else
+				func = (u8 *) __bpf_call_base + imm;
 
 			bpf_jit_emit_func_call(image, ctx, (u64)func);
 
@@ -864,6 +876,14 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 	return 0;
 }
 
+struct powerpc64_jit_data {
+	struct bpf_binary_header *header;
+	u32 *addrs;
+	u8 *image;
+	u32 proglen;
+	struct codegen_context ctx;
+};
+
 struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 {
 	u32 proglen;
@@ -871,6 +891,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	u8 *image = NULL;
 	u32 *code_base;
 	u32 *addrs;
+	struct powerpc64_jit_data *jit_data;
 	struct codegen_context cgctx;
 	int pass;
 	int flen;
@@ -878,6 +899,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	struct bpf_prog *org_fp = fp;
 	struct bpf_prog *tmp_fp;
 	bool bpf_blinded = false;
+	bool extra_pass = false;
 
 	if (!fp->jit_requested)
 		return org_fp;
@@ -891,7 +913,28 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 		fp = tmp_fp;
 	}
 
+	jit_data = fp->aux->jit_data;
+	if (!jit_data) {
+		jit_data = kzalloc(sizeof(*jit_data), GFP_KERNEL);
+		if (!jit_data) {
+			fp = org_fp;
+			goto out;
+		}
+		fp->aux->jit_data = jit_data;
+	}
+
 	flen = fp->len;
+	addrs = jit_data->addrs;
+	if (addrs) {
+		cgctx = jit_data->ctx;
+		image = jit_data->image;
+		bpf_hdr = jit_data->header;
+		proglen = jit_data->proglen;
+		alloclen = proglen + FUNCTION_DESCR_SIZE;
+		extra_pass = true;
+		goto skip_init_ctx;
+	}
+
 	addrs = kzalloc((flen+1) * sizeof(*addrs), GFP_KERNEL);
 	if (addrs == NULL) {
 		fp = org_fp;
@@ -904,10 +947,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	cgctx.stack_size = round_up(fp->aux->stack_depth, 16);
 
 	/* Scouting faux-generate pass 0 */
-	if (bpf_jit_build_body(fp, 0, &cgctx, addrs)) {
+	if (bpf_jit_build_body(fp, 0, &cgctx, addrs, false)) {
 		/* We hit something illegal or unsupported. */
 		fp = org_fp;
-		goto out;
+		goto out_addrs;
 	}
 
 	/*
@@ -925,9 +968,10 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 			bpf_jit_fill_ill_insns);
 	if (!bpf_hdr) {
 		fp = org_fp;
-		goto out;
+		goto out_addrs;
 	}
 
+skip_init_ctx:
 	code_base = (u32 *)(image + FUNCTION_DESCR_SIZE);
 
 	/* Code generation passes 1-2 */
@@ -935,7 +979,7 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 		/* Now build the prologue, body code & epilogue for real. */
 		cgctx.idx = 0;
 		bpf_jit_build_prologue(code_base, &cgctx);
-		bpf_jit_build_body(fp, code_base, &cgctx, addrs);
+		bpf_jit_build_body(fp, code_base, &cgctx, addrs, extra_pass);
 		bpf_jit_build_epilogue(code_base, &cgctx);
 
 		if (bpf_jit_enable > 1)
@@ -956,15 +1000,30 @@ struct bpf_prog *bpf_int_jit_compile(struct bpf_prog *fp)
 	((u64 *)image)[1] = local_paca->kernel_toc;
 #endif
 
+	bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
+
+	if (!fp->is_func || extra_pass) {
+		bpf_jit_binary_lock_ro(bpf_hdr);
+	} else {
+		jit_data->addrs = addrs;
+		jit_data->ctx = cgctx;
+		jit_data->proglen = proglen;
+		jit_data->image = image;
+		jit_data->header = bpf_hdr;
+	}
+
 	fp->bpf_func = (void *)image;
 	fp->jited = 1;
 	fp->jited_len = alloclen;
 
-	bpf_flush_icache(bpf_hdr, (u8 *)bpf_hdr + (bpf_hdr->pages * PAGE_SIZE));
+	if (!fp->is_func || extra_pass) {
+out_addrs:
+		kfree(addrs);
+		kfree(jit_data);
+		fp->aux->jit_data = NULL;
+	}
 
 out:
-	kfree(addrs);
-
 	if (bpf_blinded)
 		bpf_jit_prog_release_other(fp, fp == org_fp ? tmp_fp : org_fp);
 
-- 
2.14.3