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 v2 2/7] bpf: verifier, do explicit ALU32 bounds tracking
Date: Mon, 30 Mar 2020 15:23:02 -0700 [thread overview]
Message-ID: <20200330222302.6fhtedyzxfaqmthl@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <158560419880.10843.11448220440809118343.stgit@john-Precision-5820-Tower>
On Mon, Mar 30, 2020 at 02:36:39PM -0700, John Fastabend wrote:
> +static void __scalar64_min_max_lsh(struct bpf_reg_state *dst_reg,
> + u64 umin_val, u64 umax_val)
> +{
> + /* Special case <<32 because it is a common compiler pattern to zero
> + * upper bits by doing <<32 s>>32. In this case if 32bit bounds are
> + * positive we know this shift will also be positive so we can track
> + * bounds correctly. Otherwise we lose all sign bit information except
> + * what we can pick up from var_off. Perhaps we can generalize this
> + * later to shifts of any length.
> + */
> + if (umin_val == 32 && umax_val == 32 && dst_reg->s32_max_value >= 0)
> + dst_reg->smax_value = (s64)dst_reg->s32_max_value << 32;
> + else
> + dst_reg->smax_value = S64_MAX;
I fixed up above comment to say 'sign extend' instead of 'zero upper bit' and
applied.
Thanks a ton for the awesome work.
next prev parent reply other threads:[~2020-03-30 22:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-30 21:35 [bpf-next PATCH v2 0/7] ALU32 bounds tracking support John Fastabend
2020-03-30 21:36 ` [bpf-next PATCH v2 1/7] bpf: verifier, do_refine_retval_range may clamp umin to 0 incorrectly John Fastabend
2020-03-30 21:36 ` [bpf-next PATCH v2 2/7] bpf: verifier, do explicit ALU32 bounds tracking John Fastabend
2020-03-30 22:23 ` Alexei Starovoitov [this message]
2020-03-30 21:36 ` [bpf-next PATCH v2 3/7] bpf: verifier, refine 32bit bound in do_refine_retval_range John Fastabend
2020-03-30 21:37 ` [bpf-next PATCH v2 4/7] bpf: test_progs, add test to catch retval refine error handling John Fastabend
2020-03-30 21:37 ` [bpf-next PATCH v2 5/7] bpf: test_verifier, bpf_get_stack return value add <0 John Fastabend
2020-03-30 21:38 ` [bpf-next PATCH v2 6/7] bpf: test_verifier, #65 error message updates for trunc of boundary-cross John Fastabend
2020-03-30 21:38 ` [bpf-next PATCH v2 7/7] bpf: test_verifier, add alu32 bounds tracking tests John Fastabend
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