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SubjectRe: [PATCH v7 0/4] KASAN for arm64
On Mon, Nov 16, 2015 at 06:34:27PM +0300, Andrey Ryabinin wrote:
> On 11/16/2015 02:16 PM, Suzuki K. Poulose wrote:
> > On 13/10/15 09:34, Catalin Marinas wrote:
> >> On Mon, Oct 12, 2015 at 06:52:56PM +0300, Andrey Ryabinin wrote:
> >>> Andrey Ryabinin (3):
> >>> arm64: move PGD_SIZE definition to pgalloc.h
> >>> arm64: add KASAN support
> >>> Documentation/features/KASAN: arm64 supports KASAN now
> >>>
> >>> Linus Walleij (1):
> >>> ARM64: kasan: print memory assignment
> >>
> >> Patches queued for 4.4. Thanks.
> >
> > I get the following failure with KASAN + 16K_PAGES + 48BIT_VA, with 4.4-rc1:
> >
> > arch/arm64/mm/kasan_init.c: In function ‘kasan_early_init’:
> > include/linux/compiler.h:484:38: error: call to ‘__compiletime_assert_95’ declared with attribute error: BUILD_BUG_ON failed: !IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE)
> > _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> > ^
> > include/linux/compiler.h:467:4: note: in definition of macro ‘__compiletime_assert’
> > prefix ## suffix(); \
> > ^
> > include/linux/compiler.h:484:2: note: in expansion of macro ‘_compiletime_assert’
> > _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
> > ^
> > include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
> > #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
> > ^
> > include/linux/bug.h:74:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
> > BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
> > ^
> > arch/arm64/mm/kasan_init.c:95:2: note: in expansion of macro ‘BUILD_BUG_ON’
> > BUILD_BUG_ON(!IS_ALIGNED(KASAN_SHADOW_END, PGDIR_SIZE));
> >
> > The problem is that the PGDIR_SIZE is (1UL << 47) with 16K+48bit, which makes
> > the KASAN_SHADOW_END unaligned(which is aligned to (1UL << (48 - 3)) ). Is the
> > alignment really needed ? Thoughts on how best we could fix this ?
>
> Yes, it's really needed, because some code relies on this (e.g.
> clear_pgs() and kasan_init()). But it should be possible to get rid of
> this requirement.

I don't think clear_pgds() and kasan_init() are the only problems. IIUC,
kasan_populate_zero_shadow() also assumes that KASan shadow covers
multiple pgds. You need some kind of recursive writing which avoids
populating an entry which is not empty (like kasan_early_pud_populate).

--
Catalin


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