selftests/bpf: tests for rejection of ALU ops with negative offsets

These are test cases for commit [1].
Define a simple program using MOD, DIV, ADD instructions,
make sure that the program is rejected if invalid offset
field is used for instruction.

[1] 55c0ced ("bpf: Reject negative offsets for ALU ops")

Signed-off-by: Eduard Zingerman <[email protected]>

Author: eddyz87

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

@@ -3,6 +3,7 @@
 
 #include <linux/bpf.h>
 #include <bpf/bpf_helpers.h>
+#include "../../../include/linux/filter.h"
 #include "bpf_misc.h"
 
 #define MAX_ENTRIES 11
@@ -183,4 +184,32 @@ __naked void flow_keys_illegal_variable_offset_alu(void)
 	: __clobber_all);
 }
 
+#define DEFINE_BAD_OFFSET_TEST(name, op, off, imm)	\
+	SEC("socket")					\
+	__failure __msg("BPF_ALU uses reserved fields") \
+	__naked void name(void)				\
+	{						\
+		asm volatile(				\
+			"r0 = 1;"			\
+			".8byte %[insn];"		\
+			"r0 = 0;"			\
+			"exit;"				\
+		:					\
+		: __imm_insn(insn, BPF_RAW_INSN((op), 0, 0, (off), (imm))) \
+		: __clobber_all);			\
+	}
+
+/*
+ * Offset fields of 0 and 1 are legal for BPF_{DIV,MOD} instructions.
+ * Offset fields of 0 are legal for the rest of ALU instructions.
+ * Test that error is reported for illegal offsets, assuming that tests
+ * for legal offsets exist.
+ */
+DEFINE_BAD_OFFSET_TEST(bad_offset_divx, BPF_ALU64 | BPF_DIV | BPF_X, -1, 0)
+DEFINE_BAD_OFFSET_TEST(bad_offset_modk, BPF_ALU64 | BPF_MOD | BPF_K, -1, 1)
+DEFINE_BAD_OFFSET_TEST(bad_offset_addx, BPF_ALU64 | BPF_ADD | BPF_X, -1, 0)
+DEFINE_BAD_OFFSET_TEST(bad_offset_divx2, BPF_ALU64 | BPF_DIV | BPF_X, 2, 0)
+DEFINE_BAD_OFFSET_TEST(bad_offset_modk2, BPF_ALU64 | BPF_MOD | BPF_K, 2, 1)
+DEFINE_BAD_OFFSET_TEST(bad_offset_addx2, BPF_ALU64 | BPF_ADD | BPF_X, 1, 0)
+
 char _license[] SEC("license") = "GPL";