linux-kernel - Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem

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Date: Fri, 19 Apr 2024 10:32:39 -0700
From: Song Liu <song@...nel.org>
To: Mike Rapoport <rppt@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, 
	linux-kernel@...r.kernel.org, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Bjorn Topel <bjorn@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	"David S. Miller" <davem@...emloft.net>, Dinh Nguyen <dinguyen@...nel.org>, 
	Donald Dutile <ddutile@...hat.com>, Eric Chanudet <echanude@...hat.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, Helge Deller <deller@....de>, Huacai Chen <chenhuacai@...nel.org>, 
	Kent Overstreet <kent.overstreet@...ux.dev>, Luis Chamberlain <mcgrof@...nel.org>, 
	Michael Ellerman <mpe@...erman.id.au>, Nadav Amit <nadav.amit@...il.com>, 
	Palmer Dabbelt <palmer@...belt.com>, Puranjay Mohan <puranjay12@...il.com>, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, Russell King <linux@...linux.org.uk>, 
	Steven Rostedt <rostedt@...dmis.org>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
	Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...nel.org>, bpf@...r.kernel.org, 
	linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mips@...r.kernel.org, linux-mm@...ck.org, linux-modules@...r.kernel.org, 
	linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	linux-s390@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev, 
	netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()

On Fri, Apr 19, 2024 at 10:03 AM Mike Rapoport <rppt@...nel.org> wrote:
[...]
> > >
> > > [1] https://lore.kernel.org/all/20240411160526.2093408-1-rppt@kernel.org
> >
> > For the ROX to work, we need different users (module text, kprobe, etc.) to have
> > the same execmem_range. From [1]:
> >
> > static void *execmem_cache_alloc(struct execmem_range *range, size_t size)
> > {
> > ...
> >        p = __execmem_cache_alloc(size);
> >        if (p)
> >                return p;
> >       err = execmem_cache_populate(range, size);
> > ...
> > }
> >
> > We are calling __execmem_cache_alloc() without range. For this to work,
> > we can only call execmem_cache_alloc() with one execmem_range.
>
> Actually, on x86 this will "just work" because everything shares the same
> address space :)
>
> The 2M pages in the cache will be in the modules space, so
> __execmem_cache_alloc() will always return memory from that address space.
>
> For other architectures this indeed needs to be fixed with passing the
> range to __execmem_cache_alloc() and limiting search in the cache for that
> range.

I think we at least need the "map to" concept (initially proposed by Thomas)
to get this work. For example, EXECMEM_BPF and EXECMEM_KPROBE
maps to EXECMEM_MODULE_TEXT, so that all these actually share
the same range.

Does this make sense?

Song