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: <Z7AxcSwD-topj1bk@google.com>
Date: Sat, 15 Feb 2025 06:17:21 +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 Fri, Feb 14, 2025 at 07:04:13PM -0800, Alexei Starovoitov wrote:
> > > > How about:
> > > > #define BPF_LOAD_ACQ 2
> > > > #define BPF_STORE_REL 3
> > > >
> > > > and only use them with BPF_MOV like
> > > >
> > > > imm = BPF_MOV | BPF_LOAD_ACQ - is actual load acquire
> > > > imm = BPF_MOV | BPF_STORE_REL - release
> >
> > Based on everything discussed, should we proceed with the above
> > suggestion?  Specifically:
> >
> >   #define BPF_LD_ST     BPF_MOV /* 0xb0 */
> 
> The aliasing still bothers me.
> I hated doing it when going from cBPF to eBPF,
> but we only had 8-bit to work with.
> Here we have 32-bit.
> Aliases make disassemblers trickier, since value no longer
> translates to string as-is. It depends on the context.
> There is probably no use for BPF_MOV operation in atomic
> context, but by reusing BPF_ADD, BPF_XOR, etc in atomic
> we signed up ourselves for all of alu ops.

I see.

> That's why BPF_XCHG and BPF_CMPXCHG are outside
> of alu op range.
> 
> So my preference is to do:
> #define BPF_LOAD_ACQ 0x100
> #define BPF_STORE_REL 0x110
> #define BPF_CMPWAIT_RELAXED   0x120
>
> and keep growing it.
> We burn the first nibble, but so be it.

Got it!  In instruction-set.rst I'll make it clear that imm<0-3> must be
zero for load_acq/store_rel.

Cheers,
Peilin Ye