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Message-ID: <CAPhsuW7Nj1Sa_9xQtTgHz9AmX39zdh2x2COqA-qmkfpfX9hNWw@mail.gmail.com>
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>,
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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
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