linux-kernel - Re: [PATCH 1/2] mm/memblock: Add "reserve_mem" to reserved named memory at boot up

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Date: Tue, 4 Jun 2024 06:57:27 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Kees Cook <kees@...nel.org>
Cc: 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>, Kees Cook
 <keescook@...omium.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>, Mike Rapoport
 <rppt@...nel.org>, ardb@...nel.org
Subject: Re: [PATCH 1/2] mm/memblock: Add "reserve_mem" to reserved named
 memory at boot up

On Mon, 03 Jun 2024 22:52:37 -0700
Kees Cook <kees@...nel.org> wrote:

> On June 3, 2024 4:33:31 PM PDT, Steven Rostedt <rostedt@...dmis.org> wrote:
> >From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> >
> >In order to allow for requesting a memory region that can be used for
> >things like pstore on multiple machines where the memory layout is not the
> >same, add a new option to the kernel command line called "reserve_mem".
> >
> >The format is:  reserve_mem=nn:align:name
> >
> >Where it will find nn amount of memory at the given alignment of align.
> >The name field is to allow another subsystem to retrieve where the memory
> >was found. For example:
> >
> >  reserve_mem=12M:4096:oops ramoops.mem_name=oops  
> 
> How does this interact with KASLR? It has chosen its physical location
> before this parsing happens, so I'd expect this to fail once in a while,
> unless the size/alignment is lucky enough that KASLR never uses that
> portion of the physical memory...
> 

From looking at the KASLR code, it looks to me that it picks from 100
different locations. I could be wrong, but if you have sufficient memory,
I'm thinking that it should not conflict. But if it does, yes, it will fail
to pick the same location.

-- Steve