linux-kernel - Re: [PATCHv3 perf/core 0/6] uprobe,bpf: Allow to change app registers from uprobe registers

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Message-ID: <aMiFQRLP3w1APfbU@krava>
Date: Mon, 15 Sep 2025 23:29:37 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Jiri Olsa <olsajiri@...il.com>, Ihor Solodrai <ihor.solodrai@...ux.dev>,
	Oleg Nesterov <oleg@...hat.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	x86@...nel.org, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv3 perf/core 0/6] uprobe,bpf: Allow to change app
 registers from uprobe registers

On Mon, Sep 15, 2025 at 01:10:33PM -0700, Andrii Nakryiko wrote:
> On Fri, Sep 12, 2025 at 1:55 PM Jiri Olsa <olsajiri@...il.com> wrote:
> >
> > On Fri, Sep 12, 2025 at 01:28:55PM -0700, Ihor Solodrai wrote:
> > > On 9/9/25 9:41 AM, Andrii Nakryiko wrote:
> > > > On Tue, Sep 9, 2025 at 8:39 AM Jiri Olsa <jolsa@...nel.org> wrote:
> > > > >
> > > > > hi,
> > > > > we recently had several requests for tetragon to be able to change
> > > > > user application function return value or divert its execution through
> > > > > instruction pointer change.
> > > > >
> > > > > This patchset adds support for uprobe program to change app's registers
> > > > > including instruction pointer.
> > > > >
> > > > > v3 changes:
> > > > > - deny attach of kprobe,multi with kprobe_write_ctx set [Alexei]
> > > > > - added more tests for denied kprobe attachment
> > > > >
> > > > > thanks,
> > > > > jirka
> > > > >
> > > > >
> > > > > ---
> > > > > Jiri Olsa (6):
> > > > >        bpf: Allow uprobe program to change context registers
> > > > >        uprobe: Do not emulate/sstep original instruction when ip is changed
> > > > >        selftests/bpf: Add uprobe context registers changes test
> > > > >        selftests/bpf: Add uprobe context ip register change test
> > > > >        selftests/bpf: Add kprobe write ctx attach test
> > > > >        selftests/bpf: Add kprobe multi write ctx attach test
> > > > >
> > > >
> > > > For the series:
> > > >
> > > > Acked-by: Andrii Nakryiko <andrii@...nel.org>
> > > >
> > > > Question is which tree will this go through? Most changes are in BPF,
> > > > so probably bpf-next, right?
> > >
> > > Hi Jiri.
> > >
> > > This series does not apply to current bpf-next, see below.
> > >
> > > Could you please respin it with bpf-next tag?
> > > E.g. "[PATCH v4 bpf-next 0/6] ..."
> > >
> >
> > hi,
> > the uprobe change it needs to be on top of the optimized uprobes (tip/perf/core)
> 
> Is this what you happened to base it on (and thus diff context has
> that arch_uprobe_optimize), or those changes are needed for correct
> functioning?

yes

> 
> It seems like some conflict is inevitable, but on uprobe side it's two
> lines of code that would need to be put after arch_uprobe_optimize
> (instead of handler_chain), while on BPF side it's a bit more
> invasive.
> 
> So unless tip/perf/core changes are mandatory for correct functioning,
> I'd say let's rebase on top of bpf-next and handle that trivial merge
> conflict during merge window?

ok, sounds good, will rebase/resend

thanks,
jirka