selftests/bpf: Convert ctx tests from ASM to C

Convert existing tests from ASM to C, in prep for future changes to add
more comprehensive tests.

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260406194403.1649608-4-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 35 insertions, 45 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 1ac366fd4dae..169cf7fbf40f 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -175,7 +175,7 @@ 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(void)                  { RUN_TESTS(verifier_ctx); }
 void test_verifier_ctx_sk_msg(void)           { RUN(verifier_ctx_sk_msg); }
 void test_verifier_d_path(void)               { RUN(verifier_d_path); }
 void test_verifier_default_trusted_ptr(void)  { RUN_TESTS(verifier_default_trusted_ptr); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_ctx.c b/tools/testing/selftests/bpf/progs/verifier_ctx.c
index ae756764ffba..4c285ac8fff6 100644
--- a/tools/testing/selftests/bpf/progs/verifier_ctx.c
+++ b/tools/testing/selftests/bpf/progs/verifier_ctx.c
@@ -295,68 +295,58 @@ padding_access("sk_reuseport", sk_reuseport_md, hash, 4);
 SEC("syscall")
 __description("syscall: write to ctx with fixed offset")
 __success
-__naked void syscall_ctx_fixed_off_write(void)
+int syscall_ctx_fixed_off_write(void *ctx)
 {
-	asm volatile ("					\
-	r0 = 0;						\
-	*(u32*)(r1 + 0) = r0;				\
-	r1 += 4;					\
-	*(u32*)(r1 + 0) = r0;				\
-	exit;						\
-"	::: __clobber_all);
+	char *p = ctx;
+
+	*(__u32 *)p = 0;
+	*(__u32 *)(p + 4) = 0;
+	return 0;
 }
 
 /*
- * Test that program types without convert_ctx_access can dereference
- * their ctx pointer after adding a fixed offset. Variable and negative
- * offsets should still be rejected.
+ * For non-syscall program types without convert_ctx_access, direct ctx
+ * dereference is still allowed after adding a fixed offset, while variable
+ * and negative direct accesses reject.
+ *
+ * Passing ctx as a helper or kfunc memory argument is only permitted for
+ * syscall programs, so the helper and kfunc cases below validate rejection
+ * for non-syscall ctx pointers at fixed, variable, and zero-sized accesses.
  */
-#define no_rewrite_ctx_access(type, name, off, ld_op)			\
+#define no_rewrite_ctx_access(type, name, off, load_t)			\
 	SEC(type)							\
 	__description(type ": read ctx at fixed offset")		\
 	__success							\
-	__naked void no_rewrite_##name##_fixed(void)			\
+	int no_rewrite_##name##_fixed(void *ctx)			\
 	{								\
-		asm volatile ("						\
-		r1 += %[__off];						\
-		r0 = *(" #ld_op " *)(r1 + 0);				\
-		r0 = 0;							\
-		exit;"							\
-		:							\
-		: __imm_const(__off, off)				\
-		: __clobber_all);					\
+		char *p = ctx;						\
+		volatile load_t val;					\
+									\
+		val = *(load_t *)(p + off);				\
+		(void)val;						\
+		return 0;						\
 	}								\
 	SEC(type)							\
 	__description(type ": reject variable offset ctx access")	\
 	__failure __msg("variable ctx access var_off=")			\
-	__naked void no_rewrite_##name##_var(void)			\
+	int no_rewrite_##name##_var(void *ctx)			\
 	{								\
-		asm volatile ("						\
-		r6 = r1;						\
-		call %[bpf_get_prandom_u32];				\
-		r1 = r6;						\
-		r0 &= 4;						\
-		r1 += r0;						\
-		r0 = *(" #ld_op " *)(r1 + 0);				\
-		r0 = 0;							\
-		exit;"							\
-		:							\
-		: __imm(bpf_get_prandom_u32)				\
-		: __clobber_all);					\
+		__u64 off_var = bpf_get_prandom_u32();			\
+		char *p = ctx;						\
+									\
+		off_var &= 4;						\
+		p += off_var;						\
+		return *(load_t *)p;					\
 	}								\
 	SEC(type)							\
 	__description(type ": reject negative offset ctx access")	\
-	__failure __msg("negative offset ctx ptr")			\
-	__naked void no_rewrite_##name##_neg(void)			\
+	__failure __msg("invalid bpf_context access")			\
+	int no_rewrite_##name##_neg(void *ctx)			\
 	{								\
-		asm volatile ("						\
-		r1 += %[__neg_off];					\
-		r0 = *(" #ld_op " *)(r1 + 0);				\
-		r0 = 0;							\
-		exit;"							\
-		:							\
-		: __imm_const(__neg_off, -(off))			\
-		: __clobber_all);					\
+		char *p = ctx;						\
+									\
+		p -= 612;						\
+		return *(load_t *)p;					\
 	}
 
 no_rewrite_ctx_access("kprobe", kprobe, 8, u64);