selftests/bpf: subtraction bounds test

There is a bug in the verifier's handling of BPF_SUB: [a,b] - [c,d] yields
 was [a-c, b-d] rather than the correct [a-d, b-c].  So here is a test
 which, with the bogus handling, will produce ranges of [0,0] and thus
 allowed accesses; whereas the correct handling will give a range of
 [-255, 255] (and hence the right-shift will give a range of [0, 255]) and
 the accesses will be rejected.

Signed-off-by: Edward Cree <ecree@solarflare.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
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 af7d173910f4b71023badb38011a27179f92fdf9..addea82f76c943edb42ebbb6075abe849b5b7f32 100644 (file)
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -5980,6 +5980,34 @@ static struct bpf_test tests[] = {
                .result = REJECT,
                .result_unpriv = REJECT,
        },
+       {
+               "subtraction bounds (map value)",
+               .insns = {
+                       BPF_ST_MEM(BPF_DW, BPF_REG_10, -8, 0),
+                       BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -8),
+                       BPF_LD_MAP_FD(BPF_REG_1, 0),
+                       BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
+                                    BPF_FUNC_map_lookup_elem),
+                       BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 9),
+                       BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
+                       BPF_JMP_IMM(BPF_JGT, BPF_REG_1, 0xff, 7),
+                       BPF_LDX_MEM(BPF_B, BPF_REG_3, BPF_REG_0, 1),
+                       BPF_JMP_IMM(BPF_JGT, BPF_REG_3, 0xff, 5),
+                       BPF_ALU64_REG(BPF_SUB, BPF_REG_1, BPF_REG_3),
+                       BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 56),
+                       BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1),
+                       BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .fixup_map1 = { 3 },
+               .errstr_unpriv = "R0 pointer arithmetic prohibited",
+               .errstr = "R0 min value is negative, either use unsigned index or do a if (index >=0) check.",
+               .result = REJECT,
+               .result_unpriv = REJECT,
+       },
 };
 
 static int probe_filter_length(const struct bpf_insn *fp)