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bpf: Preserve const register type on const OR alu ops

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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>
This commit is contained in:
Gianluca Borello 2016-12-03 12:31:33 -08:00 committed by David S. Miller
parent f0903ea371
commit 3c839744b3
3 changed files with 68 additions and 2 deletions
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9
kernel/bpf/verifier.c
View File

@ -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;

1
tools/testing/selftests/bpf/.gitignore vendored
View File

@ -1,2 +1,3 @@
test_verifier
test_maps
test_lru_map

60
tools/testing/selftests/bpf/test_verifier.c
View File

@ -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)