From: Andrey Konovalov <andreyknvl@google.com>
To: Will Deacon <will@kernel.org>
Cc: Lecopzer Chen <lecopzer@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ard Biesheuvel <ardb@kernel.org>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Mark Brown <broonie@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Dan Williams <dan.j.williams@intel.com>,
Dmitry Vyukov <dvyukov@google.com>,
Alexander Potapenko <glider@google.com>,
gustavoars@kernel.org, kasan-dev <kasan-dev@googlegroups.com>,
Lecopzer Chen <lecopzer.chen@mediatek.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
"moderated list:ARM/Mediatek SoC..."
<linux-mediatek@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>,
Guenter Roeck <linux@roeck-us.net>,
Robin Murphy <robin.murphy@arm.com>,
rppt@kernel.org, tyhicks@linux.microsoft.com,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
yj.chiang@mediatek.com
Subject: Re: [PATCH v2 1/4] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN_VMALLOC
Date: Fri, 5 Feb 2021 21:50:55 +0100 [thread overview]
Message-ID: <CAAeHK+ysNmkxEZqQ_rEsa7bh_ZZEtOHaMstXumtzWJLu1LdDyQ@mail.gmail.com> (raw)
In-Reply-To: <20210205174301.GF22665@willie-the-truck>
On Fri, Feb 5, 2021 at 6:43 PM Will Deacon <will@kernel.org> wrote:
>
> On Fri, Feb 05, 2021 at 06:30:44PM +0100, Andrey Konovalov wrote:
> > On Fri, Feb 5, 2021 at 6:19 PM Will Deacon <will@kernel.org> wrote:
> > >
> > > On Fri, Feb 05, 2021 at 12:37:21AM +0800, Lecopzer Chen wrote:
> > > >
> > > > > On Thu, Feb 04, 2021 at 10:46:12PM +0800, Lecopzer Chen wrote:
> > > > > > > On Sat, Jan 09, 2021 at 06:32:49PM +0800, Lecopzer Chen wrote:
> > > > > > > > Linux support KAsan for VMALLOC since commit 3c5c3cfb9ef4da9
> > > > > > > > ("kasan: support backing vmalloc space with real shadow memory")
> > > > > > > >
> > > > > > > > Like how the MODULES_VADDR does now, just not to early populate
> > > > > > > > the VMALLOC_START between VMALLOC_END.
> > > > > > > > similarly, the kernel code mapping is now in the VMALLOC area and
> > > > > > > > should keep these area populated.
> > > > > > > >
> > > > > > > > Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
> > > > > > > > ---
> > > > > > > > arch/arm64/mm/kasan_init.c | 23 ++++++++++++++++++-----
> > > > > > > > 1 file changed, 18 insertions(+), 5 deletions(-)
> > > > > > > >
> > > > > > > > diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> > > > > > > > index d8e66c78440e..39b218a64279 100644
> > > > > > > > --- a/arch/arm64/mm/kasan_init.c
> > > > > > > > +++ b/arch/arm64/mm/kasan_init.c
> > > > > > > > @@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void)
> > > > > > > > {
> > > > > > > > u64 kimg_shadow_start, kimg_shadow_end;
> > > > > > > > u64 mod_shadow_start, mod_shadow_end;
> > > > > > > > + u64 vmalloc_shadow_start, vmalloc_shadow_end;
> > > > > > > > phys_addr_t pa_start, pa_end;
> > > > > > > > u64 i;
> > > > > > > >
> > > > > > > > @@ -223,6 +224,9 @@ static void __init kasan_init_shadow(void)
> > > > > > > > mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
> > > > > > > > mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
> > > > > > > >
> > > > > > > > + vmalloc_shadow_start = (u64)kasan_mem_to_shadow((void *)VMALLOC_START);
> > > > > > > > + vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END);
> > > > > > > > +
> > > > > > > > /*
> > > > > > > > * We are going to perform proper setup of shadow memory.
> > > > > > > > * At first we should unmap early shadow (clear_pgds() call below).
> > > > > > > > @@ -241,12 +245,21 @@ static void __init kasan_init_shadow(void)
> > > > > > > >
> > > > > > > > kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END),
> > > > > > > > (void *)mod_shadow_start);
> > > > > > > > - kasan_populate_early_shadow((void *)kimg_shadow_end,
> > > > > > > > - (void *)KASAN_SHADOW_END);
> > > > > > > > + if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) {
> > > > > > >
> > > > > > > Do we really need yet another CONFIG option for KASAN? What's the use-case
> > > > > > > for *not* enabling this if you're already enabling one of the KASAN
> > > > > > > backends?
> > > > > >
> > > > > > As I know, KASAN_VMALLOC now only supports KASAN_GENERIC and also
> > > > > > KASAN_VMALLOC uses more memory to map real shadow memory (1/8 of vmalloc va).
> > > > >
> > > > > The shadow is allocated dynamically though, isn't it?
> > > >
> > > > Yes, but It's still a cost.
> > > >
> > > > > > There should be someone can enable KASAN_GENERIC but can't use VMALLOC
> > > > > > due to memory issue.
> > > > >
> > > > > That doesn't sound particularly realistic to me. The reason I'm pushing here
> > > > > is because I would _really_ like to move to VMAP stack unconditionally, and
> > > > > that would effectively force KASAN_VMALLOC to be set if KASAN is in use.
> > > > >
> > > > > So unless there's a really good reason not to do that, please can we make
> > > > > this unconditional for arm64? Pretty please?
> > > >
> > > > I think it's fine since we have a good reason.
> > > > Also if someone have memory issue in KASAN_VMALLOC,
> > > > they can use SW_TAG, right?
> > > >
> > > > However the SW_TAG/HW_TAG is not supported VMALLOC yet.
> > > > So the code would be like
> > > >
> > > > if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> > >
> > > Just make this CONFIG_KASAN_VMALLOC, since that depends on KASAN_GENERIC.
> > >
> > > > /* explain the relationship between
> > > > * KASAN_GENERIC and KASAN_VMALLOC in arm64
> > > > * XXX: because we want VMAP stack....
> > > > */
> > >
> > > I don't understand the relation with SW_TAGS. The VMAP_STACK dependency is:
> > >
> > > depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
> >
> > This means that VMAP_STACK can be only enabled if KASAN_HW_TAGS=y or
> > if KASAN_VMALLOC=y for other modes.
> >
> > >
> > > which doesn't mention SW_TAGS at all. So that seems to imply that SW_TAGS
> > > and VMAP_STACK are mutually exclusive :(
> >
> > SW_TAGS doesn't yet have vmalloc support, so it's not compatible with
> > VMAP_STACK. Once vmalloc support is added to SW_TAGS, KASAN_VMALLOC
> > should be allowed to be enabled with SW_TAGS. This series is a step
> > towards having that support, but doesn't implement it. That will be a
> > separate effort.
>
> Ok, thanks. Then I think we should try to invert the dependency here, if
> possible, so that the KASAN backends depend on !VMAP_STACK if they don't
> support it, rather than silently disabling VMAP_STACK when they are
> selected.
SGTM. Not sure if I will get to this in the nearest future, so I filed
a bug: https://bugzilla.kernel.org/show_bug.cgi?id=211581
next prev parent reply other threads:[~2021-02-05 20:54 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-09 10:32 [PATCH v2 0/4] arm64: kasan: support CONFIG_KASAN_VMALLOC Lecopzer Chen
2021-01-09 10:32 ` [PATCH v2 1/4] arm64: kasan: don't populate vmalloc area for CONFIG_KASAN_VMALLOC Lecopzer Chen
2021-02-03 18:37 ` Ard Biesheuvel
2021-02-04 6:21 ` Lecopzer Chen
2021-02-04 12:45 ` Will Deacon
2021-02-04 14:46 ` Lecopzer Chen
2021-02-04 15:01 ` Will Deacon
2021-02-04 16:37 ` Lecopzer Chen
2021-02-05 17:18 ` Will Deacon
2021-02-05 17:30 ` Andrey Konovalov
2021-02-05 17:43 ` Will Deacon
2021-02-05 20:50 ` Andrey Konovalov [this message]
2021-02-05 18:10 ` Lecopzer Chen
2021-01-09 10:32 ` [PATCH v2 2/4] arm64: kasan: abstract _text and _end to KERNEL_START/END Lecopzer Chen
2021-02-04 12:46 ` Will Deacon
2021-02-04 14:51 ` Lecopzer Chen
2021-02-04 14:55 ` Will Deacon
2021-02-04 16:06 ` Lecopzer Chen
2021-02-05 17:02 ` Will Deacon
2021-01-09 10:32 ` [PATCH v2 3/4] arm64: Kconfig: support CONFIG_KASAN_VMALLOC Lecopzer Chen
2021-01-09 10:32 ` [PATCH v2 4/4] arm64: kaslr: support randomized module area with KASAN_VMALLOC Lecopzer Chen
2021-01-27 23:04 ` Will Deacon
2021-01-28 8:53 ` Lecopzer Chen
2021-01-28 20:26 ` Will Deacon
2021-01-21 10:19 ` [PATCH v2 0/4] arm64: kasan: support CONFIG_KASAN_VMALLOC Lecopzer Chen
2021-01-21 17:44 ` Andrey Konovalov
2021-01-22 19:05 ` Will Deacon
2021-02-03 18:31 ` Ard Biesheuvel
2021-02-04 12:49 ` Will Deacon
2021-02-04 15:53 ` Lecopzer Chen
2021-02-04 17:57 ` Will Deacon
2021-02-04 18:41 ` Lecopzer Chen
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