bpf: Preserve const register type on const OR alu ops

Occasionally, clang (e.g. version 3.8.1) translates a sum between two
constant operands using a BPF_OR instead of a BPF_ADD. The verifier is
currently not handling this scenario, and the destination register type
becomes UNKNOWN_VALUE even if it's still storing a constant. As a result,
the destination register cannot be used as argument to a helper function
expecting a ARG_CONST_STACK_*, limiting some use cases.

Modify the verifier to handle this case, and add a few tests to make sure
all combinations are supported, and stack boundaries are still verified
even with BPF_OR.

Signed-off-by: Gianluca Borello <g.borello@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 0e742210750ed2931a62d96febf575e8ae936d6b..38d05da84a49508d80bee58c71f7c77011b6a243 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1481,14 +1481,19 @@ static int evaluate_reg_imm_alu(struct bpf_verifier_env *env,
        struct bpf_reg_state *src_reg = &regs[insn->src_reg];
        u8 opcode = BPF_OP(insn->code);
 
-       /* dst_reg->type == CONST_IMM here, simulate execution of 'add' insn.
-        * Don't care about overflow or negative values, just add them
+       /* dst_reg->type == CONST_IMM here, simulate execution of 'add'/'or'
+        * insn. Don't care about overflow or negative values, just add them
         */
        if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_K)
                dst_reg->imm += insn->imm;
        else if (opcode == BPF_ADD && BPF_SRC(insn->code) == BPF_X &&
                 src_reg->type == CONST_IMM)
                dst_reg->imm += src_reg->imm;
+       else if (opcode == BPF_OR && BPF_SRC(insn->code) == BPF_K)
+               dst_reg->imm |= insn->imm;
+       else if (opcode == BPF_OR && BPF_SRC(insn->code) == BPF_X &&
+                src_reg->type == CONST_IMM)
+               dst_reg->imm |= src_reg->imm;
        else
                mark_reg_unknown_value(regs, insn->dst_reg);
        return 0;

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 3c59f96e3ed8c30ec083e174d8232a17de8e6308..071431bedde8fc150cfd5a7c22715d12dfeb78a6 100644 (file)
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -1,2 +1,3 @@
 test_verifier
 test_maps
+test_lru_map

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 5da2e9d7689ca150390a1c5fb1360d27d4c8cb80..8d71e44b319d73ac7fad5a7818977f7302858e8b 100644 (file)
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -2683,6 +2683,66 @@ static struct bpf_test tests[] = {
                .errstr_unpriv = "R0 pointer arithmetic prohibited",
                .result_unpriv = REJECT,
        },
+       {
+               "constant register |= constant should keep constant type",
+               .insns = {
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -48),
+                       BPF_MOV64_IMM(BPF_REG_2, 34),
+                       BPF_ALU64_IMM(BPF_OR, BPF_REG_2, 13),
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+                       BPF_EMIT_CALL(BPF_FUNC_probe_read),
+                       BPF_EXIT_INSN(),
+               },
+               .result = ACCEPT,
+               .prog_type = BPF_PROG_TYPE_TRACEPOINT,
+       },
+       {
+               "constant register |= constant should not bypass stack boundary checks",
+               .insns = {
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -48),
+                       BPF_MOV64_IMM(BPF_REG_2, 34),
+                       BPF_ALU64_IMM(BPF_OR, BPF_REG_2, 24),
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+                       BPF_EMIT_CALL(BPF_FUNC_probe_read),
+                       BPF_EXIT_INSN(),
+               },
+               .errstr = "invalid stack type R1 off=-48 access_size=58",
+               .result = REJECT,
+               .prog_type = BPF_PROG_TYPE_TRACEPOINT,
+       },
+       {
+               "constant register |= constant register should keep constant type",
+               .insns = {
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -48),
+                       BPF_MOV64_IMM(BPF_REG_2, 34),
+                       BPF_MOV64_IMM(BPF_REG_4, 13),
+                       BPF_ALU64_REG(BPF_OR, BPF_REG_2, BPF_REG_4),
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+                       BPF_EMIT_CALL(BPF_FUNC_probe_read),
+                       BPF_EXIT_INSN(),
+               },
+               .result = ACCEPT,
+               .prog_type = BPF_PROG_TYPE_TRACEPOINT,
+       },
+       {
+               "constant register |= constant register should not bypass stack boundary checks",
+               .insns = {
+                       BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),
+                       BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -48),
+                       BPF_MOV64_IMM(BPF_REG_2, 34),
+                       BPF_MOV64_IMM(BPF_REG_4, 24),
+                       BPF_ALU64_REG(BPF_OR, BPF_REG_2, BPF_REG_4),
+                       BPF_MOV64_IMM(BPF_REG_3, 0),
+                       BPF_EMIT_CALL(BPF_FUNC_probe_read),
+                       BPF_EXIT_INSN(),
+               },
+               .errstr = "invalid stack type R1 off=-48 access_size=58",
+               .result = REJECT,
+               .prog_type = BPF_PROG_TYPE_TRACEPOINT,
+       },
 };
 
 static int probe_filter_length(const struct bpf_insn *fp)