selftests/bpf: Add selftest for may_goto

Added test cases to ensure that programs with stack sizes exceeding 512
bytes are restricted in non-JITed mode, and can be executed normally in
JITed mode, even with stack sizes exceeding 512 bytes due to the presence
of may_goto instructions.

Test result:
echo "0" > /proc/sys/net/core/bpf_jit_enable
./test_progs -t verifier_stack_ptr
...
stack size 512 with may_goto with jit:SKIP
stack size 512 with may_goto without jit:OK
...
Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED

echo "1" > /proc/sys/net/core/bpf_jit_enable
./test_progs -t verifier_stack_ptr
...
stack size 512 with may_goto with jit:OK
stack size 512 with may_goto without jit:SKIP
...
Summary: 1/27 PASSED, 25 SKIPPED, 0 FAILED

Signed-off-by: Jiayuan Chen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

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

···
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("PTR_TO_STACK stack size > 512")
+__failure __msg("invalid write to stack R1 off=-520 size=8")
+__naked void stack_check_size_gt_512(void)
+{
+	asm volatile ("					\
+	r1 = r10;					\
+	r1 += -520;					\
+	r0 = 42;					\
+	*(u64*)(r1 + 0) = r0;				\
+	exit;						\
+"	::: __clobber_all);
+}
+
+#ifdef __BPF_FEATURE_MAY_GOTO
+SEC("socket")
+__description("PTR_TO_STACK stack size 512 with may_goto with jit")
+__load_if_JITed()
+__success __retval(42)
+__naked void stack_check_size_512_with_may_goto_jit(void)
+{
+	asm volatile ("					\
+	r1 = r10;					\
+	r1 += -512;					\
+	r0 = 42;					\
+	*(u32*)(r1 + 0) = r0;				\
+	may_goto l0_%=;					\
+	r2 = 100;					\
+	l0_%=:						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("socket")
+__description("PTR_TO_STACK stack size 512 with may_goto without jit")
+__load_if_no_JITed()
+__failure __msg("stack size 520(extra 8) is too large")
+__naked void stack_check_size_512_with_may_goto(void)
+{
+	asm volatile ("					\
+	r1 = r10;					\
+	r1 += -512;					\
+	r0 = 42;					\
+	*(u32*)(r1 + 0) = r0;				\
+	may_goto l0_%=;					\
+	r2 = 100;					\
+	l0_%=:						\
+	exit;						\
+"	::: __clobber_all);
+}
+#endif
+
 char _license[] SEC("license") = "GPL";