selftests/bpf: Test direct packet access on non-linear skbs

This patch adds new selftests in the direct packet access suite, to
cover the non-linear case. The first six tests cover the behavior of
the bounds check with a non-linear skb. The last test adds a call to
bpf_skb_pull_data() to be able to access the packet.

Note that the size of the linear area includes the L2 header, but for
some program types like cgroup_skb, ctx->data points to the L3 header.
Therefore, a linear area of 22 bytes will have only 8 bytes accessible
to the BPF program (22 - ETH_HLEN). For that reason, the cgroup_skb test
cases access the packet at an offset of 8 bytes.

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

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

···
 	: __clobber_all);
 }
 
+#define access_test_non_linear(name, type, desc, retval, linear_sz, off)			\
+	SEC(type)										\
+	__description("direct packet access: " #name " (non-linear, " type ", " desc ")")	\
+	__success __retval(retval)								\
+	__linear_size(linear_sz)								\
+	__naked void access_non_linear_##name(void)						\
+	{											\
+		asm volatile ("									\
+		r2 = *(u32*)(r1 + %[skb_data]);							\
+		r3 = *(u32*)(r1 + %[skb_data_end]);						\
+		r0 = r2;									\
+		r0 += %[offset];								\
+		if r0 > r3 goto l0_%=;								\
+		r0 = *(u8*)(r0 - 1);								\
+		r0 = 0;										\
+		exit;										\
+	l0_%=:	r0 = 1;										\
+		exit;										\
+	"	:										\
+		: __imm_const(skb_data, offsetof(struct __sk_buff, data)),			\
+		  __imm_const(skb_data_end, offsetof(struct __sk_buff, data_end)),		\
+		  __imm_const(offset, off)							\
+		: __clobber_all);								\
+	}
+
+access_test_non_linear(test31, "tc", "too short eth", 1, ETH_HLEN, 22);
+access_test_non_linear(test32, "tc", "too short 1", 1, 1, 22);
+access_test_non_linear(test33, "tc", "long enough", 0, 22, 22);
+access_test_non_linear(test34, "cgroup_skb/ingress", "too short eth", 1, ETH_HLEN, 8);
+access_test_non_linear(test35, "cgroup_skb/ingress", "too short 1", 1, 1, 8);
+access_test_non_linear(test36, "cgroup_skb/ingress", "long enough", 0, 22, 8);
+
+SEC("tc")
+__description("direct packet access: test37 (non-linear, linearized)")
+__success __retval(0)
+__linear_size(ETH_HLEN)
+__naked void access_non_linear_linearized(void)
+{
+	asm volatile ("				\
+	r6 = r1;				\
+	r2 = 22;				\
+	call %[bpf_skb_pull_data];		\
+	r2 = *(u32*)(r6 + %[skb_data]);		\
+	r3 = *(u32*)(r6 + %[skb_data_end]);	\
+	r0 = r2;				\
+	r0 += 22;				\
+	if r0 > r3 goto l0_%=;			\
+	r0 = *(u8*)(r0 - 1);			\
+	exit;					\
+l0_%=:	r0 = 1;					\
+	exit;					\
+"	:
+	: __imm(bpf_skb_pull_data),
+	  __imm_const(skb_data, offsetof(struct __sk_buff, data)),
+	  __imm_const(skb_data_end, offsetof(struct __sk_buff, data_end))
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";