linux-kernel - Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in deferred user space stacktrace

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Message-ID: <CAHk-=wjRC0sRZio4TkqP8_S+Fr8LUypVucPDnmERrHVjWOABXw@mail.gmail.com>
Date: Thu, 28 Aug 2025 14:06:39 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...nel.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Andrii Nakryiko <andrii@...nel.org>, 
	Indu Bhagat <indu.bhagat@...cle.com>, "Jose E. Marchesi" <jemarch@....org>, 
	Beau Belgrave <beaub@...ux.microsoft.com>, Jens Remus <jremus@...ux.ibm.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Florian Weimer <fweimer@...hat.com>, 
	Sam James <sam@...too.org>, Kees Cook <kees@...nel.org>, "Carlos O'Donell" <codonell@...hat.com>
Subject: Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in
 deferred user space stacktrace

On Thu, 28 Aug 2025 at 13:48, Steven Rostedt <rostedt@...nel.org> wrote:
>
> I could run it through the same hash algorithm that "%p" goes through so
> that it's not a real memory address.

For '%p', people can't easily trigger lots of different cases, and you
can't force kernel printouts from user space.

For something like tracing, user space *does* control the output, and
you shouldn't give people visibility into the hashing that '%p' does.

So you can certainly use siphash for hashing, but make sure to not use
the same secret key that the printing does.

As to the ID to hash, I actually think a 'struct file *' might be the
best thing to use - that's directly in the vma, no need to follow any
other pointers for it.

               Linus