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Message-ID: <20190819160320.GF9927@lakrids.cambridge.arm.com>
Date: Mon, 19 Aug 2019 17:03:20 +0100
From: Mark Rutland <mark.rutland@....com>
To: Andrey Konovalov <andreyknvl@...gle.com>
Cc: Will Deacon <will@...nel.org>,
Andrey Ryabinin <aryabinin@...tuozzo.com>,
Walter Wu <walter-zh.wu@...iatek.com>,
Alexander Potapenko <glider@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Matthias Brugger <matthias.bgg@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
wsd_upstream@...iatek.com, LKML <linux-kernel@...r.kernel.org>,
kasan-dev <kasan-dev@...glegroups.com>,
linux-mediatek@...ts.infradead.org,
Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: kasan: fix phys_to_virt() false positive on
tag-based kasan
On Mon, Aug 19, 2019 at 05:37:36PM +0200, Andrey Konovalov wrote:
> On Mon, Aug 19, 2019 at 5:03 PM Mark Rutland <mark.rutland@....com> wrote:
> >
> > On Mon, Aug 19, 2019 at 04:05:22PM +0200, Andrey Konovalov wrote:
> > > On Mon, Aug 19, 2019 at 3:34 PM Will Deacon <will@...nel.org> wrote:
> > > >
> > > > On Mon, Aug 19, 2019 at 02:23:48PM +0100, Mark Rutland wrote:
> > > > > On Mon, Aug 19, 2019 at 01:56:26PM +0100, Will Deacon wrote:
> > > > > > On Mon, Aug 19, 2019 at 07:44:20PM +0800, Walter Wu wrote:
> > > > > > > __arm_v7s_unmap() call iopte_deref() to translate pyh_to_virt address,
> > > > > > > but it will modify pointer tag into 0xff, so there is a false positive.
> > > > > > >
> > > > > > > When enable tag-based kasan, phys_to_virt() function need to rewrite
> > > > > > > its original pointer tag in order to avoid kasan report an incorrect
> > > > > > > memory corruption.
> > > > > >
> > > > > > Hmm. Which tree did you see this on? We've recently queued a load of fixes
> > > > > > in this area, but I /thought/ they were only needed after the support for
> > > > > > 52-bit virtual addressing in the kernel.
> > > > >
> > > > > I'm seeing similar issues in the virtio blk code (splat below), atop of
> > > > > the arm64 for-next/core branch. I think this is a latent issue, and
> > > > > people are only just starting to test with KASAN_SW_TAGS.
> > > > >
> > > > > It looks like the virtio blk code will round-trip a SLUB-allocated pointer from
> > > > > virt->page->virt, losing the per-object tag in the process.
> > > > >
> > > > > Our page_to_virt() seems to get a per-page tag, but this only makes
> > > > > sense if you're dealing with the page allocator, rather than something
> > > > > like SLUB which carves a page into smaller objects giving each object a
> > > > > distinct tag.
> > > > >
> > > > > Any round-trip of a pointer from SLUB is going to lose the per-object
> > > > > tag.
> > > >
> > > > Urgh, I wonder how this is supposed to work?
> > > >
> > > > If we end up having to check the KASAN shadow for *_to_virt(), then why
> > > > do we need to store anything in the page flags at all? Andrey?
> > >
> > > As per 2813b9c0 ("kasan, mm, arm64: tag non slab memory allocated via
> > > pagealloc") we should only save a non-0xff tag in page flags for non
> > > slab pages.
> > >
> > > Could you share your .config so I can reproduce this?
> >
> > I wrote a test (below) to do so. :)
> >
> > It fires with arm64 defconfig, + CONFIG_TEST_KASAN=m.
> >
> > With Andrey Ryabinin's patch it works as expected with no KASAN splats
> > for the two new test cases.
>
> OK, Andrey's patch makes sense and fixes both Mark's test patch and
> reports from CONFIG_IOMMU_IO_PGTABLE_ARMV7S_SELFTEST.
>
> Tested-by: Andrey Konovalov <andreyknvl@...gle.com>
> Reviewed-by: Andrey Konovalov <andreyknvl@...gle.com>
>
> on both patches.
>
> >
> > Thanks,
> > Mark.
> >
> > ---->8----
> > From 7e8569b558fca21ad4e80fddae659591bc84ce1f Mon Sep 17 00:00:00 2001
> > From: Mark Rutland <mark.rutland@....com>
> > Date: Mon, 19 Aug 2019 15:39:32 +0100
> > Subject: [PATCH] lib/test_kasan: add roundtrip tests
> >
> > In several places we needs to be able to operate on pointers which have
>
> "needs" => "need"
Thanks!
I'll spin a standalone v2 of this with that fixed and your tags folded
in.
Mark.
>
> > gone via a roundtrip:
> >
> > virt -> {phys,page} -> virt
> >
> > With KASAN_SW_TAGS, we can't preserve the tag for SLUB objects, and the
> > {phys,page} -> virt conversion will use KASAN_TAG_KERNEL.
> >
> > This patch adds tests to ensure that this works as expected, without
> > false positives.
> >
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> > Cc: Andrey Konovalov <andreyknvl@...gle.com>
> > Cc: Will Deacon <will.deacon@....com>
> > ---
> > lib/test_kasan.c | 40 ++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 40 insertions(+)
> >
> > diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> > index b63b367a94e8..cf7b93f0d90c 100644
> > --- a/lib/test_kasan.c
> > +++ b/lib/test_kasan.c
> > @@ -19,6 +19,8 @@
> > #include <linux/string.h>
> > #include <linux/uaccess.h>
> >
> > +#include <asm/page.h>
> > +
> > /*
> > * Note: test functions are marked noinline so that their names appear in
> > * reports.
> > @@ -337,6 +339,42 @@ static noinline void __init kmalloc_uaf2(void)
> > kfree(ptr2);
> > }
> >
> > +static noinline void __init kfree_via_page(void)
> > +{
> > + char *ptr;
> > + size_t size = 8;
> > + struct page *page;
> > + unsigned long offset;
> > +
> > + pr_info("invalid-free false positive (via page)\n");
> > + ptr = kmalloc(size, GFP_KERNEL);
> > + if (!ptr) {
> > + pr_err("Allocation failed\n");
> > + return;
> > + }
> > +
> > + page = virt_to_page(ptr);
> > + offset = offset_in_page(ptr);
> > + kfree(page_address(page) + offset);
> > +}
> > +
> > +static noinline void __init kfree_via_phys(void)
> > +{
> > + char *ptr;
> > + size_t size = 8;
> > + phys_addr_t phys;
> > +
> > + pr_info("invalid-free false positive (via phys)\n");
> > + ptr = kmalloc(size, GFP_KERNEL);
> > + if (!ptr) {
> > + pr_err("Allocation failed\n");
> > + return;
> > + }
> > +
> > + phys = virt_to_phys(ptr);
> > + kfree(phys_to_virt(phys));
> > +}
> > +
> > static noinline void __init kmem_cache_oob(void)
> > {
> > char *p;
> > @@ -737,6 +775,8 @@ static int __init kmalloc_tests_init(void)
> > kmalloc_uaf();
> > kmalloc_uaf_memset();
> > kmalloc_uaf2();
> > + kfree_via_page();
> > + kfree_via_phys();
> > kmem_cache_oob();
> > memcg_accounted_kmem_cache();
> > kasan_stack_oob();
> > --
> > 2.11.0
> >
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