From: Mark Rutland <mark.rutland@arm.com>
To: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>,
Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Andrey Konovalov <andreyknvl@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Christoph Lameter <cl@linux.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Dmitriy Vyukov <dvyukov@google.com>,
Eric Dumazet <edumazet@google.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Hillf Danton <hdanton@sina.com>, Ingo Molnar <mingo@redhat.com>,
Jann Horn <jannh@google.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Jonathan Corbet <corbet@lwn.net>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Kees Cook <keescook@chromium.org>,
Pekka Enberg <penberg@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
SeongJae Park <sjpark@amazon.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vlastimil Babka <vbabka@suse.cz>,
the arch/x86 maintainers <x86@kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64
Date: Thu, 8 Oct 2020 11:45:01 +0100 [thread overview]
Message-ID: <20201008104501.GB72325@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CANpmjNMFrMZybOebFwJ1GRXpt8v39AN016UDgPZzE8J3zKh9RA@mail.gmail.com>
On Thu, Oct 08, 2020 at 11:40:52AM +0200, Marco Elver wrote:
> On Thu, 1 Oct 2020 at 19:58, Mark Rutland <mark.rutland@arm.com> wrote:
> [...]
> > > > If you need virt_to_page() to work, the address has to be part of the
> > > > linear/direct map.
> [...]
> >
> > What's the underlying requirement here? Is this a performance concern,
> > codegen/codesize, or something else?
>
> It used to be performance, since is_kfence_address() is used in the
> fast path. However, with some further tweaks we just did to
> is_kfence_address(), our benchmarks show a pointer load can be
> tolerated.
Great!
I reckon that this is something we can optimize in futue if necessary
(e.g. with some form of code-patching for immediate values), but it's
good to have a starting point that works everywhere!
[...]
> > I'm not too worried about allocating this dynamically, but:
> >
> > * The arch code needs to set up the translation tables for this, as we
> > cannot safely change the mapping granularity live.
> >
> > * As above I'm fairly certain x86 needs to use a carevout from the
> > linear map to function correctly anyhow, so we should follow the same
> > approach for both arm64 and x86. That might be a static carevout that
> > we figure out the aliasing for, or something entirely dynamic.
>
> We're going with dynamically allocating the pool (for both x86 and
> arm64), since any benefits we used to measure from the static pool are
> no longer measurable (after removing a branch from
> is_kfence_address()). It should hopefully simplify a lot of things,
> given all the caveats that you pointed out.
>
> For arm64, the only thing left then is to fix up the case if the
> linear map is not forced to page granularity.
The simplest way to do this is to modify arm64's arch_add_memory() to
force the entire linear map to be mapped at page granularity when KFENCE
is enabled, something like:
| diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
| index 936c4762dadff..f6eba0642a4a3 100644
| --- a/arch/arm64/mm/mmu.c
| +++ b/arch/arm64/mm/mmu.c
| @@ -1454,7 +1454,8 @@ int arch_add_memory(int nid, u64 start, u64 size,
| {
| int ret, flags = 0;
|
| - if (rodata_full || debug_pagealloc_enabled())
| + if (rodata_full || debug_pagealloc_enabled() ||
| + IS_ENABLED(CONFIG_KFENCE))
| flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
|
| __create_pgd_mapping(swapper_pg_dir, start, __phys_to_virt(start),
... and I given that RODATA_FULL_DEFAULT_ENABLED is the default, I
suspect it's not worth trying to only for that for the KFENCE region
unless someone complains.
Thanks,
Mark.
next prev parent reply other threads:[~2020-10-08 10:45 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-21 13:26 [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Marco Elver
2020-09-21 13:26 ` [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure Marco Elver
2020-09-25 11:23 ` SeongJae Park
2020-09-25 11:31 ` Marco Elver
2020-09-29 12:42 ` Andrey Konovalov
2020-09-29 13:11 ` Marco Elver
2020-09-29 13:48 ` Andrey Konovalov
2020-09-29 13:49 ` Marco Elver
2020-09-29 14:01 ` Andrey Konovalov
2020-09-29 14:24 ` Mark Rutland
2020-09-29 14:51 ` Marco Elver
2020-09-29 15:05 ` Mark Rutland
2020-10-05 16:00 ` Alexander Potapenko
2020-10-05 16:49 ` Jann Horn
2020-09-29 15:51 ` Alexander Potapenko
2020-10-01 18:11 ` Mark Rutland
2020-09-21 13:26 ` [PATCH v3 02/10] x86, kfence: enable KFENCE for x86 Marco Elver
2020-09-21 13:26 ` [PATCH v3 03/10] arm64, kfence: enable KFENCE for ARM64 Marco Elver
2020-09-21 14:31 ` Will Deacon
2020-09-21 14:58 ` Alexander Potapenko
2020-09-21 15:37 ` Alexander Potapenko
2020-09-21 17:43 ` Will Deacon
2020-09-22 9:56 ` Marco Elver
2020-09-29 13:53 ` Mark Rutland
2020-09-29 16:52 ` Alexander Potapenko
2020-09-25 15:25 ` Alexander Potapenko
2020-09-29 14:02 ` Mark Rutland
2020-10-01 11:24 ` Alexander Potapenko
2020-10-01 17:57 ` Mark Rutland
2020-10-08 9:40 ` Marco Elver
2020-10-08 10:45 ` Mark Rutland [this message]
2020-10-14 19:12 ` Marco Elver
2020-10-15 13:39 ` Mark Rutland
2020-10-15 14:15 ` Marco Elver
2020-09-28 11:53 ` Marco Elver
2020-09-29 14:27 ` Mark Rutland
2020-09-29 17:04 ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 04/10] mm, kfence: insert KFENCE hooks for SLAB Marco Elver
2020-09-21 13:26 ` [PATCH v3 05/10] mm, kfence: insert KFENCE hooks for SLUB Marco Elver
2020-09-21 13:26 ` [PATCH v3 06/10] kfence, kasan: make KFENCE compatible with KASAN Marco Elver
2020-09-29 12:20 ` Andrey Konovalov
2020-09-29 13:13 ` Alexander Potapenko
2020-09-21 13:26 ` [PATCH v3 07/10] kfence, kmemleak: make KFENCE compatible with KMEMLEAK Marco Elver
2020-09-21 13:26 ` [PATCH v3 08/10] kfence, lockdep: make KFENCE compatible with lockdep Marco Elver
2020-09-21 13:26 ` [PATCH v3 09/10] kfence, Documentation: add KFENCE documentation Marco Elver
2020-09-21 13:26 ` [PATCH v3 10/10] kfence: add test suite Marco Elver
2020-09-21 17:13 ` Paul E. McKenney
2020-09-21 17:37 ` Marco Elver
2020-09-21 17:48 ` Paul E. McKenney
2020-09-21 13:38 ` [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector Dmitry Vyukov
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