selftests/bpf: Support non-linear flag in test loader

This patch adds support for a new tag __linear_size in the test loader,
to specify the size of the linear area in case of non-linear skbs. If
the tag is absent or null, a linear skb is crafted.

Signed-off-by: Paul Chaignon <[e-mail]>
Signed-off-by: Martin KaFai Lau <[e-mail]>
Link: https://patch.msgid.link/7ad92[e-mail]

tools/testing/selftests/bpf/progs/bpf_misc.h

···
  *                   Several __arch_* annotations could be specified at once.
  *                   When test case is not run on current arch it is marked as skipped.
  * __caps_unpriv     Specify the capabilities that should be set when running the test.
+ *
+ * __linear_size     Specify the size of the linear area of non-linear skbs, or
+ *                   0 for linear skbs.
  */
 #define __msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_msg=" XSTR(__COUNTER__) "=" msg)))
 #define __not_msg(msg)		__attribute__((btf_decl_tag("comment:test_expect_not_msg=" XSTR(__COUNTER__) "=" msg)))
···
 #define __stderr_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_stderr_unpriv=" XSTR(__COUNTER__) "=" msg)))
 #define __stdout(msg)		__attribute__((btf_decl_tag("comment:test_expect_stdout=" XSTR(__COUNTER__) "=" msg)))
 #define __stdout_unpriv(msg)	__attribute__((btf_decl_tag("comment:test_expect_stdout_unpriv=" XSTR(__COUNTER__) "=" msg)))
+#define __linear_size(sz)	__attribute__((btf_decl_tag("comment:test_linear_size=" XSTR(sz))))
 
 /* Define common capabilities tested using __caps_unpriv */
 #define CAP_NET_ADMIN		12

tools/testing/selftests/bpf/progs/verifier_direct_packet_access.c

···
 // SPDX-License-Identifier: GPL-2.0
 /* Converted from tools/testing/selftests/bpf/verifier/direct_packet_access.c */
 
+#include <linux/if_ether.h>
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"

tools/testing/selftests/bpf/test_loader.c

···
 #define TEST_TAG_EXPECT_STDERR_PFX_UNPRIV "comment:test_expect_stderr_unpriv="
 #define TEST_TAG_EXPECT_STDOUT_PFX "comment:test_expect_stdout="
 #define TEST_TAG_EXPECT_STDOUT_PFX_UNPRIV "comment:test_expect_stdout_unpriv="
+#define TEST_TAG_LINEAR_SIZE "comment:test_linear_size="
 
 /* Warning: duplicated in bpf_misc.h */
 #define POINTER_VALUE	0xbadcafe
···
 	int mode_mask;
 	int arch_mask;
 	int load_mask;
+	int linear_sz;
 	bool auxiliary;
 	bool valid;
 };
···
 					      &spec->unpriv.stdout);
 			if (err)
 				goto cleanup;
+		} else if (str_has_pfx(s, TEST_TAG_LINEAR_SIZE)) {
+			switch (bpf_program__type(prog)) {
+			case BPF_PROG_TYPE_SCHED_ACT:
+			case BPF_PROG_TYPE_SCHED_CLS:
+			case BPF_PROG_TYPE_CGROUP_SKB:
+				val = s + sizeof(TEST_TAG_LINEAR_SIZE) - 1;
+				err = parse_int(val, &spec->linear_sz, "test linear size");
+				if (err)
+					goto cleanup;
+				break;
+			default:
+				PRINT_FAIL("__linear_size for unsupported program type");
+				err = -EINVAL;
+				goto cleanup;
+			}
 		}
 	}
 
···
 	}
 }
 
-static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts)
+static int do_prog_test_run(int fd_prog, int *retval, bool empty_opts, int linear_sz)
 {
 	__u8 tmp_out[TEST_DATA_LEN << 2] = {};
 	__u8 tmp_in[TEST_DATA_LEN] = {};
+	struct __sk_buff ctx = {};
 	int err, saved_errno;
 	LIBBPF_OPTS(bpf_test_run_opts, topts,
 		.data_in = tmp_in,
···
 		.data_size_out = sizeof(tmp_out),
 		.repeat = 1,
 	);
+
+	if (linear_sz) {
+		ctx.data_end = linear_sz;
+		topts.ctx_in = &ctx;
+		topts.ctx_size_in = sizeof(ctx);
+	}
 
 	if (empty_opts) {
 		memset(&topts, 0, sizeof(struct bpf_test_run_opts));
···
 		}
 
 		err = do_prog_test_run(bpf_program__fd(tprog), &retval,
-				       bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false);
+				       bpf_program__type(tprog) == BPF_PROG_TYPE_SYSCALL ? true : false,
+				       spec->linear_sz);
 		if (!err && retval != subspec->retval && subspec->retval != POINTER_VALUE) {
 			PRINT_FAIL("Unexpected retval: %d != %d\n", retval, subspec->retval);
 			goto tobj_cleanup;