From: Marco Elver <elver@google.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will.deacon@arm.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Peter Collingbourne <pcc@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Branislav Rankov <Branislav.Rankov@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/12] kasan, mm: optimize krealloc poisoning
Date: Wed, 3 Feb 2021 15:34:59 +0100 [thread overview]
Message-ID: <YBq0k2p5eudcY6bD@elver.google.com> (raw)
In-Reply-To: <431c6cfa0ac8fb2b33d7ab561a64aa84c844d1a0.1612208222.git.andreyknvl@google.com>
On Mon, Feb 01, 2021 at 08:43PM +0100, Andrey Konovalov wrote:
> Currently, krealloc() always calls ksize(), which unpoisons the whole
> object including the redzone. This is inefficient, as kasan_krealloc()
> repoisons the redzone for objects that fit into the same buffer.
>
> This patch changes krealloc() instrumentation to use uninstrumented
> __ksize() that doesn't unpoison the memory. Instead, kasan_kreallos()
> is changed to unpoison the memory excluding the redzone.
>
> For objects that don't fit into the old allocation, this patch disables
> KASAN accessibility checks when copying memory into a new object instead
> of unpoisoning it.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
> mm/kasan/common.c | 12 ++++++++++--
> mm/slab_common.c | 20 ++++++++++++++------
> 2 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index 9c64a00bbf9c..a51d6ea580b0 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -476,7 +476,7 @@ static void *____kasan_kmalloc(struct kmem_cache *cache, const void *object,
>
> /*
> * The object has already been unpoisoned by kasan_slab_alloc() for
> - * kmalloc() or by ksize() for krealloc().
> + * kmalloc() or by kasan_krealloc() for krealloc().
> */
>
> /*
> @@ -526,7 +526,7 @@ void * __must_check __kasan_kmalloc_large(const void *ptr, size_t size,
>
> /*
> * The object has already been unpoisoned by kasan_alloc_pages() for
> - * alloc_pages() or by ksize() for krealloc().
> + * alloc_pages() or by kasan_krealloc() for krealloc().
> */
>
> /*
> @@ -554,8 +554,16 @@ void * __must_check __kasan_krealloc(const void *object, size_t size, gfp_t flag
> if (unlikely(object == ZERO_SIZE_PTR))
> return (void *)object;
>
> + /*
> + * Unpoison the object's data.
> + * Part of it might already have been unpoisoned, but it's unknown
> + * how big that part is.
> + */
> + kasan_unpoison(object, size);
> +
> page = virt_to_head_page(object);
>
> + /* Piggy-back on kmalloc() instrumentation to poison the redzone. */
> if (unlikely(!PageSlab(page)))
> return __kasan_kmalloc_large(object, size, flags);
> else
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index dad70239b54c..821f657d38b5 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -1140,19 +1140,27 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size,
> void *ret;
> size_t ks;
>
> - if (likely(!ZERO_OR_NULL_PTR(p)) && !kasan_check_byte(p))
> - return NULL;
> -
> - ks = ksize(p);
> + /* Don't use instrumented ksize to allow precise KASAN poisoning. */
> + if (likely(!ZERO_OR_NULL_PTR(p))) {
> + if (!kasan_check_byte(p))
> + return NULL;
> + ks = __ksize(p);
> + } else
> + ks = 0;
>
This unfortunately broke KFENCE:
https://syzkaller.appspot.com/bug?extid=e444e1006d07feef0ef3 + various
other false positives.
We need to use ksize() here, as __ksize() is unaware of KFENCE. Or
somehow add the same check here that ksize() uses to get the real object
size.
> + /* If the object still fits, repoison it precisely. */
> if (ks >= new_size) {
> p = kasan_krealloc((void *)p, new_size, flags);
> return (void *)p;
> }
>
> ret = kmalloc_track_caller(new_size, flags);
> - if (ret && p)
> - memcpy(ret, p, ks);
> + if (ret && p) {
> + /* Disable KASAN checks as the object's redzone is accessed. */
> + kasan_disable_current();
> + memcpy(ret, kasan_reset_tag(p), ks);
> + kasan_enable_current();
> + }
>
> return ret;
> }
> --
> 2.30.0.365.g02bc693789-goog
>
next prev parent reply other threads:[~2021-02-03 14:37 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-01 19:43 [PATCH 00/12] kasan: optimizations and fixes for HW_TAGS Andrey Konovalov
2021-02-01 19:43 ` [PATCH 01/12] kasan, mm: don't save alloc stacks twice Andrey Konovalov
2021-02-02 16:06 ` Marco Elver
2021-02-02 18:01 ` Andrey Konovalov
2021-02-02 18:40 ` Marco Elver
2021-02-01 19:43 ` [PATCH 02/12] kasan, mm: optimize kmalloc poisoning Andrey Konovalov
2021-02-02 16:25 ` Marco Elver
2021-02-02 17:15 ` Andrey Konovalov
2021-02-02 17:39 ` Marco Elver
2021-02-01 19:43 ` [PATCH 03/12] kasan: optimize large " Andrey Konovalov
2021-02-02 16:57 ` Marco Elver
2021-02-01 19:43 ` [PATCH 04/12] kasan: clean up setting free info in kasan_slab_free Andrey Konovalov
2021-02-02 17:03 ` Marco Elver
2021-02-01 19:43 ` [PATCH 05/12] kasan: unify large kfree checks Andrey Konovalov
2021-02-03 12:13 ` Marco Elver
2021-02-01 19:43 ` [PATCH 06/12] kasan: rework krealloc tests Andrey Konovalov
2021-02-03 14:48 ` Marco Elver
2021-02-01 19:43 ` [PATCH 07/12] kasan, mm: remove krealloc side-effect Andrey Konovalov
2021-02-03 15:10 ` Marco Elver
2021-02-01 19:43 ` [PATCH 08/12] kasan, mm: optimize krealloc poisoning Andrey Konovalov
2021-02-03 14:34 ` Marco Elver [this message]
2021-02-01 19:43 ` [PATCH 09/12] kasan: ensure poisoning size alignment Andrey Konovalov
2021-02-03 15:31 ` Marco Elver
2021-02-01 19:43 ` [PATCH 10/12] arm64: kasan: simplify and inline MTE functions Andrey Konovalov
2021-02-01 22:44 ` Andrew Morton
2021-02-04 12:39 ` Vincenzo Frascino
2021-02-02 15:42 ` Catalin Marinas
2021-02-02 18:04 ` Andrey Konovalov
2021-02-04 12:37 ` Vincenzo Frascino
2021-02-01 19:43 ` [PATCH 11/12] kasan: always inline HW_TAGS helper functions Andrey Konovalov
2021-02-03 15:51 ` Marco Elver
2021-02-01 19:43 ` [PATCH 12/12] arm64: kasan: export MTE symbols for KASAN tests Andrey Konovalov
2021-02-02 10:46 ` Will Deacon
2021-02-02 13:42 ` Andrey Konovalov
2021-02-02 15:43 ` Catalin Marinas
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