[PATCH bpf-next v2 03/22] bpf: Apply single-instruction patches of the verifier in place

[Qiliang Yuan]

bpf_patch_insn_data() replaces one instruction by one in place, and
only sets non_stack_access of its aux data from whether the new
instruction accesses memory.

bpf_patch_list_add() queues such a patch like any other, although it
moves nothing, and the commit fills in its aux data the way it does
for a longer patch, which keeps non_stack_access of the old
instruction where bpf_patch_insn_data() recomputes it.

Write a patch of a single instruction to the program right away and
adjust its aux data with adjust_insn_aux_data(), as
bpf_patch_insn_data() does.

Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 kernel/bpf/fixups.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/fixups.c b/kernel/bpf/fixups.c
index 0697f66b1ffc1..a0dd582312d86 100644
--- a/kernel/bpf/fixups.c
+++ b/kernel/bpf/fixups.c
@@ -382,7 +382,8 @@ struct bpf_prog *bpf_patch_insn_data(struct bpf_verifier_env *env, u32 off,
 
 /*
  * Queue the replacement of insn 'off' by 'patch[0..len)' until
- * bpf_patch_list_commit(), see __bpf_patch_list_add().
+ * bpf_patch_list_commit(), see __bpf_patch_list_add(). Replacing one insn by
+ * one moves nothing and is done right away.
  */
 struct bpf_insn *bpf_patch_list_add(struct bpf_verifier_env *env, u32 off,
 				    const struct bpf_insn *patch, u32 len)
@@ -397,6 +398,13 @@ struct bpf_insn *bpf_patch_list_add(struct bpf_verifier_env *env, u32 off,
 			    env, "insn %u patched out of order", off))
 		return ERR_PTR(-EFAULT);
 
+	if (len == 1) {
+		env->prog->insnsi[off] = *patch;
+		adjust_insn_aux_data(env, env->prog, off, 1, NULL,
+				     BPF_PATCH_KEEP_TARGET);
+		return &env->prog->insnsi[off];
+	}
+
 	return __bpf_patch_list_add(pl, env->prog, off, patch, len);
 }
 

-- 
2.43.0