[PATCH bpf-next 2/2] selftests/bpf: Add tests for bpf_sockopt is_compat field

["Maciej Żenczykowski" <maze@google.com>]

Sync tools/include/uapi/linux/bpf.h with the addition of the 'is_compat'
field in 'struct bpf_sockopt' and add test cases to 'prog_tests/sockopt.c'
to verify context access permissions:

 - Test reading 'ctx->is_compat' in 'cgroup/{g,s}etsockopt'
   (expecting 0 in native execution).
 - Check verifier rejects writes to 'ctx->is_compat'
   in 'cgroup/{g,s}etsockopt'.

Tested via:
  tools/testing/selftests/bpf/vmtest.sh -- ./test_progs -t sockopt

Signed-off-by: Maciej Żenczykowski <maze@google.com>
---
 tools/include/uapi/linux/bpf.h                |  1 +
 .../selftests/bpf/prog_tests/sockopt.c        | 86 +++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index ffd96e8b920b..15f712b5b164 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7616,6 +7616,7 @@ struct bpf_sockopt {
 	__s32	optname;
 	__s32	optlen;
 	__s32	retval;
+	__s32	is_compat;
 };
 
 struct bpf_pidns_info {
diff --git a/tools/testing/selftests/bpf/prog_tests/sockopt.c b/tools/testing/selftests/bpf/prog_tests/sockopt.c
index eaac83a7f388..c7dd22d0e3f8 100644
--- a/tools/testing/selftests/bpf/prog_tests/sockopt.c
+++ b/tools/testing/selftests/bpf/prog_tests/sockopt.c
@@ -215,6 +215,49 @@ static struct sockopt_test {
 		.get_optname = IP_TOS,
 		.get_optlen = 1,
 	},
+	{
+		.descr = "getsockopt: read ctx->is_compat",
+		.insns = {
+			/* r6 = ctx->is_compat */
+			BPF_LDX_MEM(BPF_W, BPF_REG_6, BPF_REG_1,
+				    offsetof(struct bpf_sockopt, is_compat)),
+
+			/* if (ctx->is_compat == 0) { */
+			BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 4),
+			/* ctx->retval = 0 */
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct bpf_sockopt, retval)),
+			/* return 1 */
+			BPF_MOV64_IMM(BPF_REG_0, 1),
+			BPF_JMP_A(1),
+			/* } else { */
+			/* return 0 */
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			/* } */
+			BPF_EXIT_INSN(),
+		},
+		.attach_type = BPF_CGROUP_GETSOCKOPT,
+		.expected_attach_type = BPF_CGROUP_GETSOCKOPT,
+
+		.get_level = SOL_IP,
+		.get_optname = IP_TOS,
+		.get_optlen = 1,
+	},
+	{
+		.descr = "getsockopt: deny writing to ctx->is_compat",
+		.insns = {
+			/* ctx->is_compat = 1 */
+			BPF_MOV64_IMM(BPF_REG_0, 1),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct bpf_sockopt, is_compat)),
+			BPF_EXIT_INSN(),
+		},
+		.attach_type = BPF_CGROUP_GETSOCKOPT,
+		.expected_attach_type = BPF_CGROUP_GETSOCKOPT,
+
+		.error = DENY_LOAD,
+	},
 	{
 		.descr = "getsockopt: deny writing to ctx->optname",
 		.insns = {
@@ -609,6 +652,49 @@ static struct sockopt_test {
 		.get_optval = { 1 << 3 },
 		.get_optlen = 1,
 	},
+	{
+		.descr = "setsockopt: read ctx->is_compat",
+		.insns = {
+			/* r6 = ctx->is_compat */
+			BPF_LDX_MEM(BPF_W, BPF_REG_6, BPF_REG_1,
+				    offsetof(struct bpf_sockopt, is_compat)),
+
+			/* if (ctx->is_compat == 0) { */
+			BPF_JMP_IMM(BPF_JNE, BPF_REG_6, 0, 4),
+			/* ctx->optlen = -1 */
+			BPF_MOV64_IMM(BPF_REG_0, -1),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct bpf_sockopt, optlen)),
+			/* return 1 */
+			BPF_MOV64_IMM(BPF_REG_0, 1),
+			BPF_JMP_A(1),
+			/* } else { */
+			/* return 0 */
+			BPF_MOV64_IMM(BPF_REG_0, 0),
+			/* } */
+			BPF_EXIT_INSN(),
+		},
+		.attach_type = BPF_CGROUP_SETSOCKOPT,
+		.expected_attach_type = BPF_CGROUP_SETSOCKOPT,
+
+		.set_optname = 123,
+		.set_optlen = 1,
+		.io_uring_support = true,
+	},
+	{
+		.descr = "setsockopt: deny writing to ctx->is_compat",
+		.insns = {
+			/* ctx->is_compat = 1 */
+			BPF_MOV64_IMM(BPF_REG_0, 1),
+			BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+				    offsetof(struct bpf_sockopt, is_compat)),
+			BPF_EXIT_INSN(),
+		},
+		.attach_type = BPF_CGROUP_SETSOCKOPT,
+		.expected_attach_type = BPF_CGROUP_SETSOCKOPT,
+
+		.error = DENY_LOAD,
+	},
 	{
 		.descr = "setsockopt: read ctx->optlen",
 		.insns = {
-- 
2.55.0.691.gc56d675ccc-goog