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Commit 3c839744 authored by Gianluca Borello's avatar Gianluca Borello Committed by David S. Miller
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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: default avatarGianluca Borello <g.borello@gmail.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f0903ea3

kernel/bpf/verifier.c

+7 −2
Original line number Diff line number Diff line
@@ -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;

tools/testing/selftests/bpf/.gitignore

+1 −0
Original line number Diff line number Diff line 
test_verifier

test_maps

test_lru_map

tools/testing/selftests/bpf/test_verifier.c

+60 −0
Original line number Diff line number Diff line
@@ -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)