netdev - Re: [RFC bpf-next] bpf, verifier: improve signed ranges inference for BPF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAM=Ch06FP+emu3s_2_XNVm1CPfBkf_Ei-xuJgsN=DWM7FFEtxA@mail.gmail.com>
Date: Fri, 2 Aug 2024 17:30:21 -0400
From: Harishankar Vishwanathan <harishankar.vishwanathan@...il.com>
To: Shung-Hsi Yu <shung-hsi.yu@...e.com>
Cc: Xu Kuohai <xukuohai@...weicloud.com>, Eduard Zingerman <eddyz87@...il.com>, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, 
	Andrii Nakryiko <andrii@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Roberto Sassu <roberto.sassu@...wei.com>, 
	Edward Cree <ecree.xilinx@...il.com>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Santosh Nagarakatte <santosh.nagarakatte@...gers.edu>, 
	Srinivas Narayana <srinivas.narayana@...gers.edu>, Matan Shachnai <m.shachnai@...gers.edu>
Subject: Re: [RFC bpf-next] bpf, verifier: improve signed ranges inference for BPF_AND

On Tue, Jul 30, 2024 at 12:26 AM Shung-Hsi Yu <shung-hsi.yu@...e.com> wrote:
[...]
> That is great to hear and really boost the level of confidence. Though I
> did made an update[1] to the patch such that implementation of
> negative_bit_floor() is change from
>
>         v &= v >> 1;
>         v &= v >> 2;
>         v &= v >> 4;
>         v &= v >> 8;
>         v &= v >> 16;
>         v &= v >> 32;
>         return v;
>
> to one that closer resembles tnum_range()
>
>         u8 bits = fls64(~v); /* find most-significant unset bit */
>         u64 delta;
>
>         /* special case, needed because 1ULL << 64 is undefined */
>         if (bits > 63)
>                 return 0;
>
>         delta = (1ULL << bits) - 1;
>         return ~delta;
>

This [1] is indeed the version of the patch that we checked: the one that
uses fls and fls64 in negative_bit_floor and negative32_bit_floor .
I replied here because you had CCed us in this thread.

Note that for checking in Agni, the implementation of fls and fls64 were
borrowed from asm-generic [2,3,4].

Having said that, the patch [1] looks good to me.
Tested-by: Harishankar Vishwanathan <harishankar.vishwanathan@...il.com>

[1]: https://lore.kernel.org/bpf/20240719081702.137173-1-shung-hsi.yu@suse.com/
[2]: https://elixir.bootlin.com/linux/v6.10/source/include/asm-generic/bitops/fls.h#L43
[3]: https://elixir.bootlin.com/linux/v6.10/source/include/asm-generic/bitops/fls64.h#L19
[4]: https://elixir.bootlin.com/linux/v6.10/source/include/asm-generic/bitops/__fls.h#L45