linux-kernel - Re: bpf: test_verifier: sanitation: alu with different scalars

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Date:   Tue, 25 Jun 2019 11:39:24 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Yauheni Kaliuta <yauheni.kaliuta@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Jiri Benc <jbenc@...hat.com>
Subject: Re: bpf: test_verifier: sanitation: alu with different scalars

On 06/25/2019 10:29 AM, Yauheni Kaliuta wrote:
> Hi!
> 
> I'm wondering, how the sanitaion tests (#903 5.2-rc6 for example)
> are supposed to work on BE arches:
> 
> {
> 	"sanitation: alu with different scalars 1",
> 	.insns = {
> 	BPF_MOV64_IMM(BPF_REG_0, 1),
> 	BPF_LD_MAP_FD(BPF_REG_ARG1, 0),
> 	BPF_MOV64_REG(BPF_REG_ARG2, BPF_REG_FP),
> 	BPF_ALU64_IMM(BPF_ADD, BPF_REG_ARG2, -16),
> 	BPF_ST_MEM(BPF_DW, BPF_REG_FP, -16, 0),
> 	BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
> 	BPF_JMP_IMM(BPF_JNE, BPF_REG_0, 0, 1),
> 	BPF_EXIT_INSN(),
> 	BPF_LDX_MEM(BPF_B, BPF_REG_1, BPF_REG_0, 0),
> 
> reads one byte 0 on BE and 28 on LE (from ->index) since
> 
> 	struct test_val {
> 		unsigned int index;
> 		int foo[MAX_ENTRIES];
> 	};
> 
>         struct test_val value = {
> 		.index = (6 + 1) * sizeof(int),
> 		.foo[6] = 0xabcdef12,
> 	};
> 
> 	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3),
> 
> So different branches are taken depending of the endianness.
> 
> 	BPF_MOV64_IMM(BPF_REG_2, 0),
> 	BPF_MOV64_IMM(BPF_REG_3, 0x100000),
> 	BPF_JMP_A(2),
> 	BPF_MOV64_IMM(BPF_REG_2, 42),
> 	BPF_MOV64_IMM(BPF_REG_3, 0x100001),
> 	BPF_ALU64_REG(BPF_ADD, BPF_REG_2, BPF_REG_3),
> 	BPF_MOV64_REG(BPF_REG_0, BPF_REG_2),
> 	BPF_EXIT_INSN(),
> 	},
> 	.fixup_map_array_48b = { 1 },
> 	.result = ACCEPT,
> 	.retval = 0x100000,
> },

Let me get my hands on a s390x box later today and get back to you.

Thanks,
Daniel