Merge branch 'bpf-dedup-fixes'

Andrii Nakryiko says:

====================
This patchset fixes a bug in btf_dedup() algorithm, which under specific
hash collision causes infinite loop. It also exposes ability to tune BTF
deduplication table size, with double purpose of allowing applications to
adjust size according to the size of BTF data, as well as allowing a simple
way to force hash collisions by setting table size to 1.

- Patch #1 fixes bug in btf_dedup testing code that's checking strings
- Patch #2 fixes pointer arg formatting in btf.h
- Patch #3 adds option to specify custom dedup table size
- Patch #4 fixes aforementioned bug in btf_dedup
- Patch #5 adds test that validates the fix

v1->v2:
- remove "Fixes" from formatting change patch
- extract roundup_pow2_max func for dedup table size
- btf_equal_struct -> btf_shallow_equal_struct
- explain in comment why we can't rely on just btf_dedup_is_equiv
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 48 insertions, 2 deletions

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index e47168d1257d..3b74d23fffab 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -14,6 +14,7 @@ feature
 test_libbpf_open
 test_sock
 test_sock_addr
+test_sock_fields
 urandom_read
 test_btf
 test_sockmap
diff --git a/tools/testing/selftests/bpf/test_btf.c b/tools/testing/selftests/bpf/test_btf.c
index 02d314383a9c..38797aa627a7 100644
--- a/tools/testing/selftests/bpf/test_btf.c
+++ b/tools/testing/selftests/bpf/test_btf.c
@@ -5732,6 +5732,51 @@ const struct btf_dedup_test dedup_tests[] = {
 	},
 },
 {
+	.descr = "dedup: struct <-> fwd resolution w/ hash collision",
+	/*
+	 * // CU 1:
+	 * struct x;
+	 * struct s {
+	 *	struct x *x;
+	 * };
+	 * // CU 2:
+	 * struct x {};
+	 * struct s {
+	 *	struct x *x;
+	 * };
+	 */
+	.input = {
+		.raw_types = {
+			/* CU 1 */
+			BTF_FWD_ENC(NAME_TBD, 0 /* struct fwd */),	/* [1] fwd x      */
+			BTF_PTR_ENC(1),					/* [2] ptr -> [1] */
+			BTF_STRUCT_ENC(NAME_TBD, 1, 8),			/* [3] struct s   */
+				BTF_MEMBER_ENC(NAME_TBD, 2, 0),
+			/* CU 2 */
+			BTF_STRUCT_ENC(NAME_TBD, 0, 0),			/* [4] struct x   */
+			BTF_PTR_ENC(4),					/* [5] ptr -> [4] */
+			BTF_STRUCT_ENC(NAME_TBD, 1, 8),			/* [6] struct s   */
+				BTF_MEMBER_ENC(NAME_TBD, 5, 0),
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0x\0s\0x\0x\0s\0x\0"),
+	},
+	.expect = {
+		.raw_types = {
+			BTF_PTR_ENC(3),					/* [1] ptr -> [3] */
+			BTF_STRUCT_ENC(NAME_TBD, 1, 8),			/* [2] struct s   */
+				BTF_MEMBER_ENC(NAME_TBD, 1, 0),
+			BTF_STRUCT_ENC(NAME_NTH(2), 0, 0),		/* [3] struct x   */
+			BTF_END_RAW,
+		},
+		BTF_STR_SEC("\0s\0x"),
+	},
+	.opts = {
+		.dont_resolve_fwds = false,
+		.dedup_table_size = 1, /* force hash collisions */
+	},
+},
+{
 	.descr = "dedup: all possible kinds (no duplicates)",
 	.input = {
 		.raw_types = {
@@ -5936,9 +5981,9 @@ static int do_test_dedup(unsigned int test_num)
 	}
 
 	test_hdr = test_btf_data;
-	test_strs = test_btf_data + test_hdr->str_off;
+	test_strs = test_btf_data + sizeof(*test_hdr) + test_hdr->str_off;
 	expect_hdr = expect_btf_data;
-	expect_strs = expect_btf_data + expect_hdr->str_off;
+	expect_strs = expect_btf_data + sizeof(*test_hdr) + expect_hdr->str_off;
 	if (CHECK(test_hdr->str_len != expect_hdr->str_len,
 		  "test_hdr->str_len:%u != expect_hdr->str_len:%u",
 		  test_hdr->str_len, expect_hdr->str_len)) {