selftests/bpf: variable offset negative tests

Variable ctx accesses and stack accesses aren't allowed, because we can't
 determine what type of value will be read.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 876b878..65aa562 100644 (file)
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -5980,6 +5980,47 @@ static struct bpf_test tests[] = {
                .errstr = "R0 min value is negative, either use unsigned index or do a if (index >=0) check.",
                .result = REJECT,
        },
+       {
+               "variable-offset ctx access",
+               .insns = {
+                       /* Get an unknown value */
+                       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
+                       /* Make it small and 4-byte aligned */
+                       BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
+                       /* add it to skb.  We now have either &skb->len or
+                        * &skb->pkt_type, but we don't know which
+                        */
+                       BPF_ALU64_REG(BPF_ADD, BPF_REG_1, BPF_REG_2),
+                       /* dereference it */
+                       BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .errstr = "variable ctx access var_off=(0x0; 0x4)",
+               .result = REJECT,
+               .prog_type = BPF_PROG_TYPE_LWT_IN,
+       },
+       {
+               "variable-offset stack access",
+               .insns = {
+                       /* Fill the top 8 bytes of the stack */
+                       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+                       /* Get an unknown value */
+                       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, 0),
+                       /* Make it small and 4-byte aligned */
+                       BPF_ALU64_IMM(BPF_AND, BPF_REG_2, 4),
+                       BPF_ALU64_IMM(BPF_SUB, BPF_REG_2, 8),
+                       /* add it to fp.  We now have either fp-4 or fp-8, but
+                        * we don't know which
+                        */
+                       BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_10),
+                       /* dereference it */
+                       BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_2, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .errstr = "variable stack access var_off=(0xfffffffffffffff8; 0x4)",
+               .result = REJECT,
+               .prog_type = BPF_PROG_TYPE_LWT_IN,
+       },
 };
 
 static int probe_filter_length(const struct bpf_insn *fp)