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Subject[PATCH v3 net-next 12/12] selftests/bpf: variable offset negative tests
Date
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>
---
tools/testing/selftests/bpf/test_verifier.c | 41 +++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 7df3c34..471fbee 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -5311,6 +5311,47 @@ 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)
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