selftests/bpf: Add a test case to write into .rodata

Add a test case which attempts to write into .rodata section of the
BPF program, and for comparison this adds test cases also for .bss
and .data section.

Before fix:

  # ./vmtest.sh -- ./test_progs -t verifier_const
  [...]
  ./test_progs -t verifier_const
  tester_init:PASS:tester_log_buf 0 nsec
  process_subtest:PASS:obj_open_mem 0 nsec
  process_subtest:PASS:specs_alloc 0 nsec
  run_subtest:PASS:obj_open_mem 0 nsec
  run_subtest:FAIL:unexpected_load_success unexpected success: 0
  torvalds#465/1   verifier_const/rodata: write rejected:FAIL
  torvalds#465/2   verifier_const/bss: write accepted:OK
  torvalds#465/3   verifier_const/data: write accepted:OK
  torvalds#465     verifier_const:FAIL
  [...]

After fix:

  # ./vmtest.sh -- ./test_progs -t verifier_const
  [...]
  ./test_progs -t verifier_const
  torvalds#465/1   verifier_const/rodata: write rejected:OK
  torvalds#465/2   verifier_const/bss: write accepted:OK
  torvalds#465/3   verifier_const/data: write accepted:OK
  torvalds#465     verifier_const:OK
  [...]

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>

tools/testing/selftests/bpf/prog_tests/verifier.c

@@ -21,6 +21,7 @@
 #include "verifier_cgroup_inv_retcode.skel.h"
 #include "verifier_cgroup_skb.skel.h"
 #include "verifier_cgroup_storage.skel.h"
+#include "verifier_const.skel.h"
 #include "verifier_const_or.skel.h"
 #include "verifier_ctx.skel.h"
 #include "verifier_ctx_sk_msg.skel.h"
@@ -146,6 +147,7 @@ void test_verifier_cfg(void)                  { RUN(verifier_cfg); }
 void test_verifier_cgroup_inv_retcode(void)   { RUN(verifier_cgroup_inv_retcode); }
 void test_verifier_cgroup_skb(void)           { RUN(verifier_cgroup_skb); }
 void test_verifier_cgroup_storage(void)       { RUN(verifier_cgroup_storage); }
+void test_verifier_const(void)                { RUN(verifier_const); }
 void test_verifier_const_or(void)             { RUN(verifier_const_or); }
 void test_verifier_ctx(void)                  { RUN(verifier_ctx); }
 void test_verifier_ctx_sk_msg(void)           { RUN(verifier_ctx_sk_msg); }

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

@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024 Isovalent */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+const volatile long foo = 42;
+long bar;
+long bart = 96;
+
+SEC("tc/ingress")
+__description("rodata: write rejected")
+__failure __msg("write into map forbidden")
+int tcx1(struct __sk_buff *skb)
+{
+	char buff[] = { '8', '4', '\0' };
+	bpf_strtol(buff, sizeof(buff), 0, (long *)&foo);
+	return TCX_PASS;
+}
+
+SEC("tc/ingress")
+__description("bss: write accepted")
+__success
+int tcx2(struct __sk_buff *skb)
+{
+	char buff[] = { '8', '4', '\0' };
+	bpf_strtol(buff, sizeof(buff), 0, &bar);
+	return TCX_PASS;
+}
+
+SEC("tc/ingress")
+__description("data: write accepted")
+__success
+int tcx3(struct __sk_buff *skb)
+{
+	char buff[] = { '8', '4', '\0' };
+	bpf_strtol(buff, sizeof(buff), 0, &bart);
+	return TCX_PASS;
+}
+
+char LICENSE[] SEC("license") = "GPL";