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From: Song Liu <song@kernel.org>
Date: Fri, 19 Apr 2024 10:32:39 -0700
Message-ID: <CAPhsuW7Nj1Sa_9xQtTgHz9AmX39zdh2x2COqA-qmkfpfX9hNWw@mail.gmail.com>
Subject: Re: [PATCH v4 05/15] mm: introduce execmem_alloc() and execmem_free()
To: Mike Rapoport <rppt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>, Peter Zijlstra <peterz@infradead.org>, 
	linux-kernel@vger.kernel.org, Alexandre Ghiti <alexghiti@rivosinc.com>, 
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On Fri, Apr 19, 2024 at 10:03=E2=80=AFAM Mike Rapoport <rppt@kernel.org> wr=
ote:
[...]
> > >
> > > [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 si=
ze)
> > {
> > ...
> >        p =3D __execmem_cache_alloc(size);
> >        if (p)
> >                return p;
> >       err =3D 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 tha=
t
> 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