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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: John Fastabend <john.fastabend@gmail.com>
Cc: ecree@solarflare.com, yhs@fb.com, daniel@iogearbox.net,
	netdev@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [bpf-next PATCH 10/10] bpf: test_verifier, add alu32 bounds tracking tests
Date: Wed, 25 Mar 2020 23:34:41 -0700
Message-ID: <20200326063441.ymitkh5z6sgevbm4@ast-mbp> (raw)
In-Reply-To: <158507165554.15666.6019652542965367828.stgit@john-Precision-5820-Tower>

On Tue, Mar 24, 2020 at 10:40:55AM -0700, John Fastabend wrote:
> Its possible to have divergent ALU32 and ALU64 bounds when using JMP32
> instructins and ALU64 arithmatic operations. Sometimes the clang will
> even generate this code. Because the case is a bit tricky lets add
> a specific test for it.
> 
> Here is  pseudocode asm version to illustrate the idea,
> 
>  1 r0 = 0xffffffff00000001;
>  2 if w0 > 1 goto %l[fail];
>  3 r0 += 1
>  5 if w0 > 2 goto %l[fail]
>  6 exit
> 
> The intent here is the verifier will fail the load if the 32bit bounds
> are not tracked correctly through ALU64 op. Similarly we can check the
> 64bit bounds are correctly zero extended after ALU32 ops.
> 
>  1 r0 = 0xffffffff00000001;
>  2 w0 += 1
>  2 if r0 < 0xffffffff00000001 goto %l[fail];

This should be 3.

> +	"bounds check mixed 32bit and 64bit arithmatic. test2",
> +	.insns = {
> +	BPF_MOV64_IMM(BPF_REG_0, 0),
> +	BPF_MOV64_IMM(BPF_REG_1, -1),
> +	BPF_ALU64_IMM(BPF_LSH, BPF_REG_1, 32),
> +	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 1),
> +	/* r1 = 0xffffFFFF00000001 */
> +	BPF_MOV64_IMM(BPF_REG_2, 3),
> +	/* r1 = 0x2 */
> +	BPF_ALU32_IMM(BPF_ADD, BPF_REG_1, 1),
> +	/* check ALU32 op zero extends 64bit bounds */
> +	BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_2, 1),
> +	BPF_JMP_A(1),
> +	/* invalid ldx if bounds are lost above */
> +	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, -1),
> +	BPF_EXIT_INSN(),
> +	},
> +	.result = ACCEPT
> +},
> 

      reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 17:37 [bpf-next PATCH 00/10] ALU32 bounds tracking support John Fastabend
2020-03-24 17:37 ` [bpf-next PATCH 01/10] bpf: verifier, do_refine_retval_range may clamp umin to 0 incorrectly John Fastabend
2020-03-24 17:38 ` [bpf-next PATCH 02/10] bpf: verifer, refactor adjust_scalar_min_max_vals John Fastabend
2020-03-26  6:10   ` Alexei Starovoitov
2020-03-24 17:38 ` [bpf-next PATCH 03/10] bpf: verifer, adjust_scalar_min_max_vals to always call update_reg_bounds() John Fastabend
2020-03-24 17:38 ` [bpf-next PATCH 04/10] bpf: verifier, do explicit ALU32 bounds tracking John Fastabend
2020-03-26  6:20   ` Alexei Starovoitov
2020-03-26 15:18     ` John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 05/10] bpf: verifier, return value is an int in do_refine_retval_range John Fastabend
2020-03-26  6:23   ` Alexei Starovoitov
2020-03-26 15:52     ` John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 06/10] bpf: test_progs, add test to catch retval refine error handling John Fastabend
2020-03-24 17:39 ` [bpf-next PATCH 07/10] bpf: test_verifier, bpf_get_stack return value add <0 John Fastabend
2020-03-26  6:33   ` Alexei Starovoitov
2020-03-26 15:48     ` John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 08/10] bpf: test_verifier, #70 error message updates for 32-bit right shift John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 09/10] bpf: test_verifier, #65 error message updates for trunc of boundary-cross John Fastabend
2020-03-24 17:40 ` [bpf-next PATCH 10/10] bpf: test_verifier, add alu32 bounds tracking tests John Fastabend
2020-03-26  6:34   ` Alexei Starovoitov [this message]

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