[PATCH bpf-next v2 13/22] bpf: Allow inserting in front of a queued patch

[Qiliang Yuan <odys.yuan@gmail.com>]

bpf_convert_ctx_accesses() inserts the store of the context pointer
for the epilogue in front of the first instruction, and then the
prologue in front of it as well.

bpf_patch_list_insert() only takes an instruction that has no patch
queued yet, so the second insertion is refused.

Put insns inserted in front of a queued patch in front of all of it,
and move the patch down behind them the same way as a single
instruction.

Signed-off-by: Qiliang Yuan <odys.yuan@gmail.com>
---
 kernel/bpf/core.c   | 27 +++++++++++++++------------
 kernel/bpf/fixups.c |  2 +-
 2 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 6e356e16613b3..0447e3b4cfa48 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -746,24 +746,27 @@ int __bpf_patch_list_del(struct bpf_patch_list *pl, const struct bpf_prog *prog,
  * Queue 'insns[0..cnt)' to go in front of insn 'off'. Jumps to 'off',
  * instruction arrays and poke descriptors still name the insn at 'off', while
  * subprogs, line info, function pointers and calls that start at 'off' start
- * at the first inserted insn.
+ * at the first inserted insn. Inserting in front of a queued patch puts the
+ * insns in front of it.
  */
 int __bpf_patch_list_insert(struct bpf_patch_list *pl, const struct bpf_prog *prog,
 			    u32 off, const struct bpf_insn *insns, u32 cnt)
 {
-	struct bpf_insn_patch *p;
+	struct bpf_insn_patch *p = pl->cnt ? &pl->patches[pl->cnt - 1] : NULL;
 	int err;
 
-	err = patch_list_reserve_patch(pl) ?: patch_list_reserve_insns(pl, 1);
-	if (err)
-		return err;
-	p = &pl->patches[pl->cnt++];
-	p->off = off;
-	p->len = 1;
-	p->target = 0;
-	p->start = pl->insn_cnt;
-	p->orig = prog->insnsi[off];
-	pl->insns[pl->insn_cnt++] = p->orig;
+	if (!p || off != p->off) {
+		err = patch_list_reserve_patch(pl) ?: patch_list_reserve_insns(pl, 1);
+		if (err)
+			return err;
+		p = &pl->patches[pl->cnt++];
+		p->off = off;
+		p->len = 1;
+		p->target = 0;
+		p->start = pl->insn_cnt;
+		p->orig = prog->insnsi[off];
+		pl->insns[pl->insn_cnt++] = p->orig;
+	}
 
 	err = patch_list_reserve_insns(pl, cnt);
 	if (err)
diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
index bb4fd75a70624..6d99de1be2581 100644
--- a/kernel/bpf/fixups.c
+++ b/kernel/bpf/fixups.c
@@ -429,7 +429,7 @@ int bpf_patch_list_insert(struct bpf_verifier_env *env, u32 off,
 		return -EINTR;
 
 	if (verifier_bug_if(!cnt || off >= env->prog->len ||
-			    (p && off <= p->off),
+			    (p && (off < p->off || (off == p->off && !p->len))),
 			    env, "insns inserted at %u out of order", off))
 		return -EFAULT;
 

-- 
2.43.0