linux-kernel - Re: [PATCH bpf-next v5 2/6] bpf/verifier: add bpf

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Date: Sun, 24 Mar 2024 15:13:08 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Benjamin Tissoires <bentiss@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, 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>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v5 2/6] bpf/verifier: add bpf_timer as a kfunc
 capable type

On Sat, Mar 23, 2024 at 9:57 PM Kumar Kartikeya Dwivedi
<memxor@...il.com> wrote:

> > > >
> > > > Observation is correct. The patch is buggy,
> > > > but the suggestion to follow process_dynptr_func() will lead
> > > > to unnecessary complexity.
> > > > dynptr-s are on stack with plenty of extra checks.
> > >
> > > The suggestion was to call process_timer_func, not process_dynptr_func.
> > >
> > > > In this case bpf_timer is in map_value.
> > > > Much simpler is to follow KF_ARG_PTR_TO_MAP approach.
> > >
> > > What I meant by the example was that dynptr handling does the same
> > > thing for kfuncs and helpers (using the same function), so timer
> > > arguments should do the same (i.e. use process_timer_func), which will
> > > do all checks for constant offset (ensuring var_off is tnum_is_const)
> > > and match it against btf_record->timer_off.
> >
> > I don't follow. Please elaborate with a patch.
> > The var_off and off is a part of the bug, but it's not the biggest part of it.
>
> Not compile tested.

I see. All makes sense to me.

Benjamin,
pls incorporate it in your set.