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Subject: Re: [PATCH v7 0/5] kasan: support backing vmalloc space with real
 shadow memory
To:     Daniel Axtens <dja@axtens.net>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, x86@kernel.org, aryabinin@virtuozzo.com,
        glider@google.com, luto@kernel.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, dvyukov@google.com
Cc:     linuxppc-dev@lists.ozlabs.org, gor@linux.ibm.com
References: <20190903145536.3390-1-dja@axtens.net>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <d43cba17-ef1f-b715-e826-5325432042dd@c-s.fr>
Date:   Wed, 11 Sep 2019 06:27:15 +0000
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Hi Daniel,

Are any other patches required prior to this series ? I have tried to 
apply it on later powerpc/merge branch without success:


[root@localhost linux-powerpc]# git am 
/root/Downloads/kasan-support-backing-vmalloc-space-with-real-shadow-memory\(1\).patch 

Applying: kasan: support backing vmalloc space with real shadow memory
.git/rebase-apply/patch:389: trailing whitespace.
  *                 (1)      (2)      (3)
error: patch failed: lib/Kconfig.kasan:142
error: lib/Kconfig.kasan: patch does not apply
Patch failed at 0001 kasan: support backing vmalloc space with real 
shadow memory
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".


[root@localhost linux-powerpc]# git am -3 
/root/Downloads/kasan-support-backing-vmalloc-space-with-real-shadow-memory\(1\).patch 

Applying: kasan: support backing vmalloc space with real shadow memory
error: sha1 information is lacking or useless (include/linux/vmalloc.h).
error: could not build fake ancestor
Patch failed at 0001 kasan: support backing vmalloc space with real 
shadow memory
The copy of the patch that failed is found in: .git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".


Christophe

On 09/03/2019 02:55 PM, Daniel Axtens wrote:
> Currently, vmalloc space is backed by the early shadow page. This
> means that kasan is incompatible with VMAP_STACK.
> 
> This series provides a mechanism to back vmalloc space with real,
> dynamically allocated memory. I have only wired up x86, because that's
> the only currently supported arch I can work with easily, but it's
> very easy to wire up other architectures, and it appears that there is
> some work-in-progress code to do this on arm64 and s390.
> 
> This has been discussed before in the context of VMAP_STACK:
>   - https://bugzilla.kernel.org/show_bug.cgi?id=202009
>   - https://lkml.org/lkml/2018/7/22/198
>   - https://lkml.org/lkml/2019/7/19/822
> 
> In terms of implementation details:
> 
> Most mappings in vmalloc space are small, requiring less than a full
> page of shadow space. Allocating a full shadow page per mapping would
> therefore be wasteful. Furthermore, to ensure that different mappings
> use different shadow pages, mappings would have to be aligned to
> KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
> 
> Instead, share backing space across multiple mappings. Allocate a
> backing page when a mapping in vmalloc space uses a particular page of
> the shadow region. This page can be shared by other vmalloc mappings
> later on.
> 
> We hook in to the vmap infrastructure to lazily clean up unused shadow
> memory.
> 
> 
> v1: https://lore.kernel.org/linux-mm/20190725055503.19507-1-dja@axtens.net/
> v2: https://lore.kernel.org/linux-mm/20190729142108.23343-1-dja@axtens.net/
>   Address review comments:
>   - Patch 1: use kasan_unpoison_shadow's built-in handling of
>              ranges that do not align to a full shadow byte
>   - Patch 3: prepopulate pgds rather than faulting things in
> v3: https://lore.kernel.org/linux-mm/20190731071550.31814-1-dja@axtens.net/
>   Address comments from Mark Rutland:
>   - kasan_populate_vmalloc is a better name
>   - handle concurrency correctly
>   - various nits and cleanups
>   - relax module alignment in KASAN_VMALLOC case
> v4: https://lore.kernel.org/linux-mm/20190815001636.12235-1-dja@axtens.net/
>   Changes to patch 1 only:
>   - Integrate Mark's rework, thanks Mark!
>   - handle the case where kasan_populate_shadow might fail
>   - poision shadow on free, allowing the alloc path to just
>       unpoision memory that it uses
> v5: https://lore.kernel.org/linux-mm/20190830003821.10737-1-dja@axtens.net/
>   Address comments from Christophe Leroy:
>   - Fix some issues with my descriptions in commit messages and docs
>   - Dynamically free unused shadow pages by hooking into the vmap book-keeping
>   - Split out the test into a separate patch
>   - Optional patch to track the number of pages allocated
>   - minor checkpatch cleanups
> v6: https://lore.kernel.org/linux-mm/20190902112028.23773-1-dja@axtens.net/
>   Properly guard freeing pages in patch 1, drop debugging code.
> v7: Add a TLB flush on freeing, thanks Mark Rutland.
>      Explain more clearly how I think freeing is concurrency-safe.
> 
> Daniel Axtens (5):
>    kasan: support backing vmalloc space with real shadow memory
>    kasan: add test for vmalloc
>    fork: support VMAP_STACK with KASAN_VMALLOC
>    x86/kasan: support KASAN_VMALLOC
>    kasan debug: track pages allocated for vmalloc shadow
> 
>   Documentation/dev-tools/kasan.rst |  63 ++++++++
>   arch/Kconfig                      |   9 +-
>   arch/x86/Kconfig                  |   1 +
>   arch/x86/mm/kasan_init_64.c       |  60 ++++++++
>   include/linux/kasan.h             |  31 ++++
>   include/linux/moduleloader.h      |   2 +-
>   include/linux/vmalloc.h           |  12 ++
>   kernel/fork.c                     |   4 +
>   lib/Kconfig.kasan                 |  16 +++
>   lib/test_kasan.c                  |  26 ++++
>   mm/kasan/common.c                 | 230 ++++++++++++++++++++++++++++++
>   mm/kasan/generic_report.c         |   3 +
>   mm/kasan/kasan.h                  |   1 +
>   mm/vmalloc.c                      |  45 +++++-
>   14 files changed, 497 insertions(+), 6 deletions(-)
>