linux-kernel - Re: [PATCH v4 0/9] uprobes: misc cleanups/simplifications

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Message-ID: <20240802092528.GF39708@noisy.programming.kicks-ass.net>
Date: Fri, 2 Aug 2024 11:25:28 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>,
	Oleg Nesterov <oleg@...hat.com>, andrii@...nel.org,
	mhiramat@...nel.org, jolsa@...nel.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v4 0/9] uprobes: misc cleanups/simplifications

On Thu, Aug 01, 2024 at 02:13:41PM -0700, Andrii Nakryiko wrote:

> Ok, this bisected to:
> 
> 675ad74989c2 ("perf/core: Add aux_pause, aux_resume, aux_start_paused")

Adrian, there are at least two obvious bugs there:

 - aux_action was key's off of PERF_PMU_CAP_AUX_OUTPUT, which is not
   right, that's the capability where events can output to AUX -- aka.
   PEBS-to-PT. It should be PERF_PMU_CAP_ITRACE, which is the
   PT/CoreSight thing.

 - it sets aux_paused unconditionally, which is scribbling in the giant
   union which is overwriting state set by perf_init_event().

But I think there's more problems, we need to do the aux_action
validation after perf_get_aux_event(), we can't know if having those
bits set makes sense before that. This means the perf_event_alloc() site
is wrong in the first place.

I'm going to drop these patches for now. Please rework.