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

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Date: Fri, 12 Apr 2024 23:59:07 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Steven Rostedt <rostedt@...dmis.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: [POC][RFC][PATCH 1/2] mm/x86: Add wildcard * option as
 memmap=nn*align:name

On Tue, Apr 09, 2024 at 04:41:24PM -0700, Kees Cook wrote:
> On Tue, Apr 09, 2024 at 07:11:56PM -0400, Steven Rostedt wrote:
> > On Tue, 9 Apr 2024 15:23:07 -0700
> > Kees Cook <keescook@...omium.org> wrote:
> > 
> > > 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?
> > 
> > Yeah, would that give the same physical memory each boot, and can we
> > guarantee that KASLR will not map the kernel over the previous location?
> 
> Hm, no, for physical memory it needs to get excluded very early, which
> means e820.

Whatever memory is reserved in arch/x86/kernel/e820.c, that happens after
kaslr, so to begin with, a new memmap parameter should be also added to
parse_memmap in arch/x86/boot/compressed/kaslr.c to ensure the same
physical address will be available after KASLR.

More generally, memmap= is x86 specific and a bit of a hack.
Why won't you add a new kernel parameter that will be parsed in, say, 
mm/mm_init.c and will create the mmap_map (or whatever it will be named)
and reserve that memory in memblock rather than in e820?

This still will require update to arch/x86/boot/compressed/kaslr.c of
course.

> So, yeah, your proposal makes sense. I'm not super excited
> about this be x86-only though. What does arm64 for for memmap?
> 
> -- 
> Kees Cook
> 

-- 
Sincerely yours,
Mike.