selftests/bpf: Test indirect var_off stack access in raw mode

Test that verifier rejects indirect access to uninitialized stack with
variable offset.

Example of output:
  # ./test_verifier
  ...
  #859/p indirect variable-offset stack access, uninitialized OK

Signed-off-by: Andrey Ignatov <rdna@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/tools/testing/selftests/bpf/verifier/var_off.c b/tools/testing/selftests/bpf/verifier/var_off.c
index c4ebd0bb07814f6c1095ea153b7c0bb065e19ed0..3840bd16e1739301343f0627fe801697979eebc0 100644 (file)
--- a/tools/testing/selftests/bpf/verifier/var_off.c
+++ b/tools/testing/selftests/bpf/verifier/var_off.c
@@ -114,6 +114,33 @@
        .result = REJECT,
        .prog_type = BPF_PROG_TYPE_LWT_IN,
 },
+{
+       "indirect variable-offset stack access, uninitialized",
+       .insns = {
+       BPF_MOV64_IMM(BPF_REG_2, 6),
+       BPF_MOV64_IMM(BPF_REG_3, 28),
+       /* Fill the top 16 bytes of the stack. */
+       BPF_ST_MEM(BPF_W, BPF_REG_10, -16, 0),
+       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+       /* Get an unknown value. */
+       BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1, 0),
+       /* Make it small and 4-byte aligned. */
+       BPF_ALU64_IMM(BPF_AND, BPF_REG_4, 4),
+       BPF_ALU64_IMM(BPF_SUB, BPF_REG_4, 16),
+       /* Add it to fp.  We now have either fp-12 or fp-16, we don't know
+        * which, but either way it points to initialized stack.
+        */
+       BPF_ALU64_REG(BPF_ADD, BPF_REG_4, BPF_REG_10),
+       BPF_MOV64_IMM(BPF_REG_5, 8),
+       /* Dereference it indirectly. */
+       BPF_EMIT_CALL(BPF_FUNC_getsockopt),
+       BPF_MOV64_IMM(BPF_REG_0, 0),
+       BPF_EXIT_INSN(),
+       },
+       .errstr = "invalid indirect read from stack var_off",
+       .result = REJECT,
+       .prog_type = BPF_PROG_TYPE_SOCK_OPS,
+},
 {
        "indirect variable-offset stack access, ok",
        .insns = {