linux-kernel - Re: [PATCH bpf-next v2 4/9] bpf: Introduce load-acquire and store-release instructions

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <Z60dO2sV6VIVNE6t@google.com>
Date: Wed, 12 Feb 2025 22:14:19 +0000
From: Peilin Ye <yepeilin@...gle.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: bpf <bpf@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	bpf@...f.org, Xu Kuohai <xukuohai@...weicloud.com>,
	Eduard Zingerman <eddyz87@...il.com>,
	David Vernet <void@...ifault.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	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@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Ilya Leoshkevich <iii@...ux.ibm.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Quentin Monnet <qmo@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	Ihor Solodrai <ihor.solodrai@...ux.dev>,
	Yingchi Long <longyingchi24s@....ac.cn>,
	Josh Don <joshdon@...gle.com>, Barret Rhoden <brho@...gle.com>,
	Neel Natu <neelnatu@...gle.com>,
	Benjamin Segall <bsegall@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 4/9] bpf: Introduce load-acquire and
 store-release instructions

On Mon, Feb 10, 2025 at 10:51:11PM +0000, Peilin Ye wrote:
> > >   #define BPF_LOAD_ACQ   0x10
> > >   #define BPF_STORE_REL  0x20
> > 
> > why not 1 and 2 ?
> 
> I just realized that we can't do 1 and 2 because BPF_ADD | BPF_FETCH
> also equals 1.
> 
> > All other bits are reserved and the verifier will make sure they're zero
> 
> IOW, we can't tell if imm<4-7> is reserved or BPF_ADD (0x00).  What
> would you suggest?  Maybe:
> 
>   #define BPF_ATOMIC_LD_ST 0x10
> 
>   #define BPF_LOAD_ACQ      0x1
>   #define BPF_STORE_REL     0x2
> 
> ?

Or, how about reusing 0xb in imm<4-7>:

  #define BPF_ATOMIC_LD_ST 0xb0

  #define BPF_LOAD_ACQ      0x1
  #define BPF_STORE_REL     0x2

0xb is BPF_MOV in BPFArithOp<>, and we'll never need it for BPF_ATOMIC.
Instead of moving values between registers, we now "move" values from/to
the memory - if I can think of it that way.

- - -
Or, do we want to start to use the remaining bits of the imm field (i.e.
imm<8-31>) ?

Thanks,
Peilin Ye