Date:   Thu,  4 Jul 2019 22:26:44 +0100
From:   Jiong Wang <jiong.wang@...ronome.com>
To:     alexei.starovoitov@...il.com, daniel@...earbox.net
Cc:     ecree@...arflare.com, naveen.n.rao@...ux.vnet.ibm.com,
        andriin@...com, jakub.kicinski@...ronome.com, bpf@...r.kernel.org,
        netdev@...r.kernel.org, oss-drivers@...ronome.com,
        Jiong Wang <jiong.wang@...ronome.com>
Subject: [RFC bpf-next 1/8] bpf: introducing list based insn patching infra to core layer

This patch introduces list based bpf insn patching infra to bpf core layer
which is lower than verification layer.

This layer has bpf insn sequence as the solo input, therefore the tasks
to be finished during list linerization is:
  - copy insn
  - relocate jumps
  - relocation line info.

Suggested-by: Alexei Starovoitov <ast@...nel.org>
Suggested-by: Edward Cree <ecree@...arflare.com>
Signed-off-by: Jiong Wang <jiong.wang@...ronome.com>
---
 include/linux/filter.h |  25 +++++
 kernel/bpf/core.c      | 268 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 293 insertions(+)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 1fe53e7..1fea68c 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -842,6 +842,31 @@ struct bpf_prog *bpf_patch_insn_single(struct bpf_prog *prog, u32 off,
 				       const struct bpf_insn *patch, u32 len);
 int bpf_remove_insns(struct bpf_prog *prog, u32 off, u32 cnt);
 
+int bpf_jit_adj_imm_off(struct bpf_insn *insn, int old_idx, int new_idx,
+			int idx_map[]);
+
+#define LIST_INSN_FLAG_PATCHED	0x1
+#define LIST_INSN_FLAG_REMOVED	0x2
+struct bpf_list_insn {
+	struct bpf_insn insn;
+	struct bpf_list_insn *next;
+	s32 orig_idx;
+	u32 flag;
+};
+
+struct bpf_list_insn *bpf_create_list_insn(struct bpf_prog *prog);
+void bpf_destroy_list_insn(struct bpf_list_insn *list);
+/* Replace LIST_INSN with new list insns generated from PATCH. */
+struct bpf_list_insn *bpf_patch_list_insn(struct bpf_list_insn *list_insn,
+					  const struct bpf_insn *patch,
+					  u32 len);
+/* Pre-patch list_insn with insns inside PATCH, meaning LIST_INSN is not
+ * touched. New list insns are inserted before it.
+ */
+struct bpf_list_insn *bpf_prepatch_list_insn(struct bpf_list_insn *list_insn,
+					     const struct bpf_insn *patch,
+					     u32 len);
+
 void bpf_clear_redirect_map(struct bpf_map *map);
 
 static inline bool xdp_return_frame_no_direct(void)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index e2c1b43..e60703e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -502,6 +502,274 @@ int bpf_remove_insns(struct bpf_prog *prog, u32 off, u32 cnt)
 	return WARN_ON_ONCE(bpf_adj_branches(prog, off, off + cnt, off, false));
 }
 
+int bpf_jit_adj_imm_off(struct bpf_insn *insn, int old_idx, int new_idx,
+			s32 idx_map[])
+{
+	u8 code = insn->code;
+	s64 imm;
+	s32 off;
+
+	if (BPF_CLASS(code) != BPF_JMP && BPF_CLASS(code) != BPF_JMP32)
+		return 0;
+
+	if (BPF_CLASS(code) == BPF_JMP &&
+	    (BPF_OP(code) == BPF_EXIT ||
+	     (BPF_OP(code) == BPF_CALL && insn->src_reg != BPF_PSEUDO_CALL)))
+		return 0;
+
+	/* BPF to BPF call. */
+	if (BPF_OP(code) == BPF_CALL) {
+		imm = idx_map[old_idx + insn->imm + 1] - new_idx - 1;
+		if (imm < S32_MIN || imm > S32_MAX)
+			return -ERANGE;
+		insn->imm = imm;
+		return 1;
+	}
+
+	/* Jump. */
+	off = idx_map[old_idx + insn->off + 1] - new_idx - 1;
+	if (off < S16_MIN || off > S16_MAX)
+		return -ERANGE;
+	insn->off = off;
+	return 0;
+}
+
+void bpf_destroy_list_insn(struct bpf_list_insn *list)
+{
+	struct bpf_list_insn *elem, *next;
+
+	for (elem = list; elem; elem = next) {
+		next = elem->next;
+		kvfree(elem);
+	}
+}
+
+struct bpf_list_insn *bpf_create_list_insn(struct bpf_prog *prog)
+{
+	unsigned int idx, len = prog->len;
+	struct bpf_list_insn *hdr, *prev;
+	struct bpf_insn *insns;
+
+	hdr = kvzalloc(sizeof(*hdr), GFP_KERNEL);
+	if (!hdr)
+		return ERR_PTR(-ENOMEM);
+
+	insns = prog->insnsi;
+	hdr->insn = insns[0];
+	hdr->orig_idx = 1;
+	prev = hdr;
+
+	for (idx = 1; idx < len; idx++) {
+		struct bpf_list_insn *node = kvzalloc(sizeof(*node),
+						      GFP_KERNEL);
+
+		if (!node) {
+			/* Destroy what has been allocated. */
+			bpf_destroy_list_insn(hdr);
+			return ERR_PTR(-ENOMEM);
+		}
+		node->insn = insns[idx];
+		node->orig_idx = idx + 1;
+		prev->next = node;
+		prev = node;
+	}
+
+	return hdr;
+}
+
+/* Linearize bpf list insn to array. */
+static struct bpf_prog *bpf_linearize_list_insn(struct bpf_prog *prog,
+						struct bpf_list_insn *list)
+{
+	u32 *idx_map, idx, prev_idx, fini_cnt = 0, orig_cnt = prog->len;
+	struct bpf_insn *insns, *insn;
+	struct bpf_list_insn *elem;
+
+	/* Calculate final size. */
+	for (elem = list; elem; elem = elem->next)
+		if (!(elem->flag & LIST_INSN_FLAG_REMOVED))
+			fini_cnt++;
+
+	insns = prog->insnsi;
+	/* If prog length remains same, nothing else to do. */
+	if (fini_cnt == orig_cnt) {
+		for (insn = insns, elem = list; elem; elem = elem->next, insn++)
+			*insn = elem->insn;
+		return prog;
+	}
+	/* Realloc insn buffer when necessary. */
+	if (fini_cnt > orig_cnt)
+		prog = bpf_prog_realloc(prog, bpf_prog_size(fini_cnt),
+					GFP_USER);
+	if (!prog)
+		return ERR_PTR(-ENOMEM);
+	insns = prog->insnsi;
+	prog->len = fini_cnt;
+
+	/* idx_map[OLD_IDX] = NEW_IDX */
+	idx_map = kvmalloc(orig_cnt * sizeof(u32), GFP_KERNEL);
+	if (!idx_map)
+		return ERR_PTR(-ENOMEM);
+	memset(idx_map, 0xff, orig_cnt * sizeof(u32));
+
+	/* Copy over insn + calculate idx_map. */
+	for (idx = 0, elem = list; elem; elem = elem->next) {
+		int orig_idx = elem->orig_idx - 1;
+
+		if (orig_idx >= 0) {
+			idx_map[orig_idx] = idx;
+
+			if (elem->flag & LIST_INSN_FLAG_REMOVED)
+				continue;
+		}
+		insns[idx++] = elem->insn;
+	}
+
+	/* Relocate jumps using idx_map.
+	 *   old_dst = jmp_insn.old_target + old_pc + 1;
+	 *   new_dst = idx_map[old_dst] = jmp_insn.new_target + new_pc + 1;
+	 *   jmp_insn.new_target = new_dst - new_pc - 1;
+	 */
+	for (idx = 0, prev_idx = 0, elem = list; elem; elem = elem->next) {
+		int ret, orig_idx;
+
+		/* A removed insn doesn't increase new_pc */
+		if (elem->flag & LIST_INSN_FLAG_REMOVED)
+			continue;
+
+		orig_idx = elem->orig_idx - 1;
+		ret = bpf_jit_adj_imm_off(&insns[idx],
+					  orig_idx >= 0 ? orig_idx : prev_idx,
+					  idx, idx_map);
+		idx++;
+		if (ret < 0) {
+			kvfree(idx_map);
+			return ERR_PTR(ret);
+		}
+		if (orig_idx >= 0)
+			/* Record prev_idx. it is used for relocating jump insn
+			 * inside patch buffer. For example, when doing jit
+			 * blinding, a jump could be moved to some other
+			 * positions inside the patch buffer, and its old_dst
+			 * could be calculated using prev_idx.
+			 */
+			prev_idx = orig_idx;
+	}
+
+	/* Adjust linfo.
+	 *
+	 * NOTE: the prog reached core layer has been adjusted to contain insns
+	 *       for single function, however linfo contains information for
+	 *       whole program, so we need to make sure linfo beyond current
+	 *       function is handled properly.
+	 */
+	if (prog->aux->nr_linfo) {
+		u32 linfo_idx, insn_start, insn_end, nr_linfo, idx, delta;
+		struct bpf_line_info *linfo;
+
+		linfo_idx = prog->aux->linfo_idx;
+		linfo = &prog->aux->linfo[linfo_idx];
+		insn_start = linfo[0].insn_off;
+		insn_end = insn_start + orig_cnt;
+		nr_linfo = prog->aux->nr_linfo - linfo_idx;
+		delta = fini_cnt - orig_cnt;
+		for (idx = 0; idx < nr_linfo; idx++) {
+			int adj_off;
+
+			if (linfo[idx].insn_off >= insn_end) {
+				linfo[idx].insn_off += delta;
+				continue;
+			}
+
+			adj_off = linfo[idx].insn_off - insn_start;
+			linfo[idx].insn_off = idx_map[adj_off] + insn_start;
+		}
+	}
+	kvfree(idx_map);
+
+	return prog;
+}
+
+struct bpf_list_insn *bpf_patch_list_insn(struct bpf_list_insn *list_insn,
+					  const struct bpf_insn *patch,
+					  u32 len)
+{
+	struct bpf_list_insn *prev, *next;
+	u32 insn_delta = len - 1;
+	u32 idx;
+
+	list_insn->insn = *patch;
+	list_insn->flag |= LIST_INSN_FLAG_PATCHED;
+
+	/* Since our patchlet doesn't expand the image, we're done. */
+	if (insn_delta == 0)
+		return list_insn;
+
+	len--;
+	patch++;
+
+	prev = list_insn;
+	next = list_insn->next;
+	for (idx = 0; idx < len; idx++) {
+		struct bpf_list_insn *node = kvzalloc(sizeof(*node),
+						      GFP_KERNEL);
+
+		if (!node) {
+			/* Link what's allocated, so list destroyer could
+			 * free them.
+			 */
+			prev->next = next;
+			return ERR_PTR(-ENOMEM);
+		}
+
+		node->insn = patch[idx];
+		prev->next = node;
+		prev = node;
+	}
+
+	prev->next = next;
+	return prev;
+}
+
+struct bpf_list_insn *bpf_prepatch_list_insn(struct bpf_list_insn *list_insn,
+					     const struct bpf_insn *patch,
+					     u32 len)
+{
+	struct bpf_list_insn *prev, *node, *begin_node;
+	u32 idx;
+
+	if (!len)
+		return list_insn;
+
+	node = kvzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return ERR_PTR(-ENOMEM);
+	node->insn = patch[0];
+	begin_node = node;
+	prev = node;
+
+	for (idx = 1; idx < len; idx++) {
+		node = kvzalloc(sizeof(*node), GFP_KERNEL);
+		if (!node) {
+			node = begin_node;
+			/* Release what's has been allocated. */
+			while (node) {
+				struct bpf_list_insn *next = node->next;
+
+				kvfree(node);
+				node = next;
+			}
+			return ERR_PTR(-ENOMEM);
+		}
+		node->insn = patch[idx];
+		prev->next = node;
+		prev = node;
+	}
+
+	prev->next = list_insn;
+	return begin_node;
+}
+
 void bpf_prog_kallsyms_del_subprogs(struct bpf_prog *fp)
 {
 	int i;
-- 
2.7.4

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