linux-hardening - Re: [PATCH v3 2/2] pstore/ramoops: Add ramoops.mem

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Message-ID: <CAMj1kXFGnk4vYpTk4PwUg8iYHcbXdrPaYP+OBxHrD5+=jvow+g@mail.gmail.com>
Date: Thu, 13 Jun 2024 16:06:47 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Mike Rapoport <rppt@...nel.org>, Kees Cook <kees@...nel.org>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, 
	Vlastimil Babka <vbabka@...e.cz>, Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Peter Zijlstra <peterz@...radead.org>, Tony Luck <tony.luck@...el.com>, 
	"Guilherme G. Piccoli" <gpiccoli@...lia.com>, linux-hardening@...r.kernel.org, 
	Guenter Roeck <linux@...ck-us.net>, Ross Zwisler <zwisler@...gle.com>, wklin@...gle.com, 
	Vineeth Remanan Pillai <vineeth@...byteword.org>, Joel Fernandes <joel@...lfernandes.org>, 
	Suleiman Souhlal <suleiman@...gle.com>, Linus Torvalds <torvalds@...uxfoundation.org>, 
	Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v3 2/2] pstore/ramoops: Add ramoops.mem_name= command line option

On Thu, 13 Jun 2024 at 15:26, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 13 Jun 2024 08:11:48 +0200
> Ard Biesheuvel <ardb@...nel.org> wrote:
> > >
> > > I've added one more comment to v5, with that fixed I can take this.
> > >
> >
> > So how is this supposed to work wrt to the rigid 'no user visible
> > regressions' rule, given that this whole thing is a best effort thing
>
> This has nothing to do with user space. The kernel command line has
> broken in the past. If you update the kernel, you can update the
> command line. There's no "no user visible regressions" rule. It's
> "Don't break user space". This has nothing to do with user space.
>
> > to begin with. This needs at least a huge disclaimer that this rule
> > does not apply, and if this works today, there is no guarantee that it
> > will keep working on newer kernels. Otherwise, you will be making the
> > job of the people who work on the boot code significantly more
> > difficult. And even then, I wonder whether Linus and #regzcop are
> > going to honour such a disclaimer.
>
> Again, this has nothing to do with user space. The rule Linus talks
> about is breaking user space. This is about kernel debugging. Something
> *completely different*!
>
> >
> > So this belongs downstream, unless some guarantees can be provided
> > that this functionality is exempt from the usual regression policies.
>
> I disagree. kexec/kdump also has the same issues.
>

Fair enough. As long as it is documented that there is no guarantee
that this will keep working over a kernel upgrade, then I have no
objections.