Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230616085038.4121892-1-rppt@kernel.org> <20230616085038.4121892-3-rppt@kernel.org>
 <f9a7eebe-d36e-4587-b99d-35d4edefdd14@app.fastmail.com> <20230618080027.GA52412@kernel.org>
 <a17c65c6-863f-4026-9c6f-a04b659e9ab4@app.fastmail.com> <20230625161417.GK52412@kernel.org>
 <ZJmFFmexl_1GUhIL@FVFF77S0Q05N>
In-Reply-To: <ZJmFFmexl_1GUhIL@FVFF77S0Q05N>
From:   Song Liu <song@kernel.org>
Date:   Mon, 26 Jun 2023 10:48:37 -0700
Message-ID: <CAPhsuW4pDkd7rCWRM6938ve36rfhGxyu=8t1-GjcKnNajofpQA@mail.gmail.com>
Subject: Re: [PATCH v2 02/12] mm: introduce execmem_text_alloc() and jit_text_alloc()
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Mike Rapoport <rppt@kernel.org>, Andy Lutomirski <luto@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "David S. Miller" <davem@davemloft.net>,
        Dinh Nguyen <dinguyen@kernel.org>,
        Heiko Carstens <hca@linux.ibm.com>,
        Helge Deller <deller@gmx.de>,
        Huacai Chen <chenhuacai@kernel.org>,
        Kent Overstreet <kent.overstreet@linux.dev>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nadav Amit <nadav.amit@gmail.com>,
        "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Puranjay Mohan <puranjay12@gmail.com>,
        Rick P Edgecombe <rick.p.edgecombe@intel.com>,
        "Russell King (Oracle)" <linux@armlinux.org.uk>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will@kernel.org>, bpf@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org,
        linux-mm@kvack.org, linux-modules@vger.kernel.org,
        linux-parisc@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-s390@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org, loongarch@lists.linux.dev,
        netdev@vger.kernel.org, sparclinux@vger.kernel.org,
        "the arch/x86 maintainers" <x86@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Jun 26, 2023 at 5:31=E2=80=AFAM Mark Rutland <mark.rutland@arm.com>=
 wrote:
>
[...]
> >
> > So the idea was that jit_text_alloc() will have a cache of large pages
> > mapped ROX, will allocate memory from those caches and there will be
> > jit_update() that uses text poking for writing to that memory.
> >
> > Upon allocation of a large page to increase the cache, that large page =
will
> > be "invalidated" by filling it with breakpoint instructions (e.g int3 o=
n
> > x86)
>
> Does that work on x86?
>
> That is in no way gauranteed for other architectures; on arm64 you need
> explicit cache maintenance (with I-cache maintenance at the VA to be exec=
uted
> from) followed by context-synchronization-events (e.g. via ISB instructio=
ns, or
> IPIs).

I guess we need:
1) Invalidate unused part of the huge ROX pages;
2) Do not put two jit users (including module text, bpf, etc.) in the
same cache line;
3) Explicit cache maintenance;
4) context-synchronization-events.

Would these (or a subset of them) be sufficient to protect us from torn rea=
d?

Thanks,
Song