bpf: Represent stack access effects with arg_access_info

The following patches in the series add support for may_write property
inference. To properly track this property there is a need to
distinguish three ways the helpers/kfuncs affect stack:
- read;
- write and destroy all previous stack tracking information for
  affected slots;
- both read and write the stack slots, potentially preserving some of
  the tracking information.

The later property can't be encoded by signed access_byte convention.
Hence, introduce arg_access_info with a size and separate may_read,
may_write and must_write bits. Convert the liveness access recording
paths to use it. Proper may_write calculation and support will be
added in the following patches.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20261009-scev-minimal-rebase-v3-1-bcba9bc53ac9@gmail.com

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index c51083c761cf..d4f32acba236 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1723,6 +1723,14 @@ bool bpf_is_may_goto_insn(struct bpf_insn *insn);
 void bpf_verbose_insn(struct bpf_verifier_env *env, struct bpf_insn *insn);
 bool bpf_get_call_summary(struct bpf_verifier_env *env, struct bpf_insn *call,
 			  struct bpf_call_summary *cs);
+/* Stack effects used for state pruning; must_write implies may_write. */
+struct arg_access_info {
+	u32 size;		/* Maximum extent; U32_MAX if unknown. */
+	u8 may_read:1;		/* Incoming contents or initialization may be needed. */
+	u8 may_write:1;
+	u8 must_write:1;	/* Prior verifier state is destroyed throughout size. */
+};
+
 s64 bpf_helper_stack_access_bytes(struct bpf_verifier_env *env,
 				  struct bpf_insn *insn, int arg,
 				  int insn_idx);