linux-hardening - Re: [POC][RFC][PATCH 1/2] mm/x86: Add wildcard * option as memmap=nn*align:name

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Date: Tue, 9 Apr 2024 15:23:07 -0700
From: Kees Cook <keescook@...omium.org>
To: Steven Rostedt <rostedt@...dmis.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>,
	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: [POC][RFC][PATCH 1/2] mm/x86: Add wildcard * option as
 memmap=nn*align:name

On Tue, Apr 09, 2024 at 05:02:55PM -0400, Steven Rostedt 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 is not the same,
> add a new option to the memmap=nn$ kernel command line.
> 
> The memmap=nn$addr will reserve nn amount of memory at the physical
> address addr. To use this, one must know the physical memory layout and
> know where usable memory exists in the physical layout.
> 
> Add a '*' option that will assign memory by looking for a range that can
> fit the given size and alignment. It will start at the high addresses, and
> then work its way down.
> 
> The format is:  memmap=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:
> 
>   memmap=12M*4096:oops ramoops.mem_name=oops
> 
> Where ramoops.mem_name will tell ramoops that memory was reserved for it
> via the wildcard '*' option and it can find it by calling:
> 
>   if (memmap_named("oops", &start, &size)) {
> 	// start holds the start address and size holds the size given
> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  arch/x86/kernel/e820.c | 91 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/mm.h     |  2 +
>  mm/memory.c            |  7 ++++
>  3 files changed, 100 insertions(+)

Do we need to involve e820 at all? I think it might be possible to just
have pstore call request_mem_region() very early? Or does KASLR make
that unstable?

-- 
Kees Cook