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From: Alexander Potapenko <glider@google.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Marco Elver <elver@google.com>,
	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@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>,
	sjpark@amazon.com,  Thomas Gleixner <tglx@linutronix.de>,
	Vlastimil Babka <vbabka@suse.cz>, Will Deacon <will@kernel.org>,
	 "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 01/10] mm: add Kernel Electric-Fence infrastructure
Date: Tue, 29 Sep 2020 17:51:58 +0200	[thread overview]
Message-ID: <CAG_fn=UOJARteeqT_+1ORPEP9SB5HR3B3W8830rA9kjZLoN+Ww@mail.gmail.com> (raw)
In-Reply-To: <20200929142411.GC53442@C02TD0UTHF1T.local>

On Tue, Sep 29, 2020 at 4:24 PM Mark Rutland <mark.rutland@arm.com> wrote:
>
> On Mon, Sep 21, 2020 at 03:26:02PM +0200, Marco Elver wrote:
> > From: Alexander Potapenko <glider@google.com>
> >
> > This adds the Kernel Electric-Fence (KFENCE) infrastructure. KFENCE is a
> > low-overhead sampling-based memory safety error detector of heap
> > use-after-free, invalid-free, and out-of-bounds access errors.
> >
> > KFENCE is designed to be enabled in production kernels, and has near
> > zero performance overhead. Compared to KASAN, KFENCE trades performance
> > for precision. The main motivation behind KFENCE's design, is that with
> > enough total uptime KFENCE will detect bugs in code paths not typically
> > exercised by non-production test workloads. One way to quickly achieve a
> > large enough total uptime is when the tool is deployed across a large
> > fleet of machines.
> >
> > KFENCE objects each reside on a dedicated page, at either the left or
> > right page boundaries. The pages to the left and right of the object
> > page are "guard pages", whose attributes are changed to a protected
> > state, and cause page faults on any attempted access to them. Such page
> > faults are then intercepted by KFENCE, which handles the fault
> > gracefully by reporting a memory access error. To detect out-of-bounds
> > writes to memory within the object's page itself, KFENCE also uses
> > pattern-based redzones. The following figure illustrates the page
> > layout:
> >
> >   ---+-----------+-----------+-----------+-----------+-----------+---
> >      | xxxxxxxxx | O :       | xxxxxxxxx |       : O | xxxxxxxxx |
> >      | xxxxxxxxx | B :       | xxxxxxxxx |       : B | xxxxxxxxx |
> >      | x GUARD x | J : RED-  | x GUARD x | RED-  : J | x GUARD x |
> >      | xxxxxxxxx | E :  ZONE | xxxxxxxxx |  ZONE : E | xxxxxxxxx |
> >      | xxxxxxxxx | C :       | xxxxxxxxx |       : C | xxxxxxxxx |
> >      | xxxxxxxxx | T :       | xxxxxxxxx |       : T | xxxxxxxxx |
> >   ---+-----------+-----------+-----------+-----------+-----------+---
> >
> > Guarded allocations are set up based on a sample interval (can be set
> > via kfence.sample_interval). After expiration of the sample interval, a
> > guarded allocation from the KFENCE object pool is returned to the main
> > allocator (SLAB or SLUB). At this point, the timer is reset, and the
> > next allocation is set up after the expiration of the interval.
>
> From other sub-threads it sounds like these addresses are not part of
> the linear/direct map.
For x86 these addresses belong to .bss, i.e. "kernel text mapping"
section, isn't that the linear map?
I also don't see lm_alias being used much outside arm64 code.

> Having kmalloc return addresses outside of the
> linear map is going to break anything that relies on virt<->phys
> conversions, and is liable to make DMA corrupt memory. There were
> problems of that sort with VMAP_STACK, and this is why kvmalloc() is
> separate from kmalloc().
>
> Have you tested with CONFIG_DEBUG_VIRTUAL? I'd expect that to scream.

Just checked - it doesn't scream on x86.

> I strongly suspect this isn't going to be safe unless you always use an
> in-place carevout from the linear map (which could be the linear alias
> of a static carevout).
>
> [...]
>
> > +static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
> > +{
> > +     return static_branch_unlikely(&kfence_allocation_key) ? __kfence_alloc(s, size, flags) :
> > +                                                                   NULL;
> > +}
>
> Minor (unrelated) nit, but this would be easier to read as:
>
> static __always_inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags)
> {
>         if (static_branch_unlikely(&kfence_allocation_key))
>                 return __kfence_alloc(s, size, flags);
>         return NULL;
> }
>
> Thanks,
> Mark.



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg


  parent reply	other threads:[~2020-09-29 15:52 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 [this message]
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
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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