From: "Liuwenliang (Abbott Liu)" <liuwenliang@huawei.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Russell King - ARM Linux <linux@armlinux.org.uk>,
Dmitry Vyukov <dvyukov@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Andrey Ryabinin" <aryabinin@virtuozzo.com>,
"afzal.mohd.ma@gmail.com" <afzal.mohd.ma@gmail.com>,
"f.fainelli@gmail.com" <f.fainelli@gmail.com>,
Laura Abbott <labbott@redhat.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Michal Hocko <mhocko@suse.com>,
"cdall@linaro.org" <cdall@linaro.org>,
"marc.zyngier@arm.com" <marc.zyngier@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
"Matthew Wilcox" <mawilcox@microsoft.com>,
Thomas Gleixner <tglx@linutronix.de>,
Thomas Garnier <thgarnie@google.com>,
Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
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"linux-mm@kvack.org" <linux-mm@kvack.org>,
Jiazhenghua <jiazhenghua@huawei.com>,
Dailei <dylix.dailei@huawei.com>,
Zengweilin <zengweilin@huawei.com>,
Heshaoliang <heshaoliang@huawei.com>
Subject: Re: [PATCH 06/11] change memory_is_poisoned_16 for aligned error
Date: Tue, 16 Jan 2018 08:39:45 +0000 [thread overview]
Message-ID: <B8AC3E80E903784988AB3003E3E97330C0070E96@dggemm510-mbs.china.huawei.com> (raw)
In-Reply-To: <CAKv+Gu94wgvC-yNHdpOr-Jyo6kC_ovA94=ik0mQYUMNV9Miahg@mail.gmail.com>
On 6 December 2017 at 1:09 Ard Biesheuvel [ard.biesheuvel@linaro.org] wrote:
>On 5 December 2017 at 14:19, Liuwenliang (Abbott Liu)
><liuwenliang@huawei.com> wrote:
>> On Nov 23, 2017 20:30 Russell King - ARM Linux [mailto:linux@armlinux.org.uk] wrote:
>>>On Thu, Oct 12, 2017 at 11:27:40AM +0000, Liuwenliang (Lamb) wrote:
>>>> >> - I don't understand why this is necessary. memory_is_poisoned_16()
>>>> >> already handles unaligned addresses?
>>>> >>
>>>> >> - If it's needed on ARM then presumably it will be needed on other
>>>> >> architectures, so CONFIG_ARM is insufficiently general.
>>>> >>
>>>> >> - If the present memory_is_poisoned_16() indeed doesn't work on ARM,
>>>> >> it would be better to generalize/fix it in some fashion rather than
>>>> >> creating a new variant of the function.
>>>>
>>>>
>>>> >Yes, I think it will be better to fix the current function rather then
>>>> >have 2 slightly different copies with ifdef's.
>>>> >Will something along these lines work for arm? 16-byte accesses are
>>>> >not too common, so it should not be a performance problem. And
>>>> >probably modern compilers can turn 2 1-byte checks into a 2-byte check
>>>> >where safe (x86).
>>>>
>>>> >static __always_inline bool memory_is_poisoned_16(unsigned long addr)
>>>> >{
>>>> > u8 *shadow_addr = (u8 *)kasan_mem_to_shadow((void *)addr);
>>>> >
>>>> > if (shadow_addr[0] || shadow_addr[1])
>>>> > return true;
>>>> > /* Unaligned 16-bytes access maps into 3 shadow bytes. */
>>>> > if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
>>>> > return memory_is_poisoned_1(addr + 15);
>>>> > return false;
>>>> >}
>>>>
>>>> Thanks for Andrew Morton and Dmitry Vyukov's review.
>>>> If the parameter addr=0xc0000008, now in function:
>>>> static __always_inline bool memory_is_poisoned_16(unsigned long addr)
>>>> {
>>>> --- //shadow_addr = (u16 *)(KASAN_OFFSET+0x18000001(=0xc0000008>>3)) is not
>>>> --- // unsigned by 2 bytes.
>>>> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
>>>>
>>>> /* Unaligned 16-bytes access maps into 3 shadow bytes. */
>>>> if (unlikely(!IS_ALIGNED(addr, KASAN_SHADOW_SCALE_SIZE)))
>>>> return *shadow_addr || memory_is_poisoned_1(addr + 15);
>>>> ---- //here is going to be error on arm, specially when kernel has not finished yet.
>>>> ---- //Because the unsigned accessing cause DataAbort Exception which is not
>>>> ---- //initialized when kernel is starting.
>>>> return *shadow_addr;
>>>> }
>>>>
>>>> I also think it is better to fix this problem.
>>
>>>What about using get_unaligned() ?
>>
>> Thanks for your review.
>>
>> I think it is good idea to use get_unaligned. But ARMv7 support CONFIG_ HAVE_EFFICIENT_UNALIGNED_ACCESS
>> (arch/arm/Kconfig : select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU).
>> So on ARMv7, the code:
>> u16 *shadow_addr = get_unaligned((u16 *)kasan_mem_to_shadow((void *)addr));
>> equals the code:000
>> u16 *shadow_addr = (u16 *)kasan_mem_to_shadow((void *)addr);
>>
>
>No it does not. The compiler may merge adjacent accesses into ldm or
>ldrd instructions, which do not tolerate misalignment regardless of
>the SCTLR.A bit.
>
>This is actually something we may need to fix for ARM, i.e., drop
>HAVE_EFFICIENT_UNALIGNED_ACCESS altogether, or carefully review the
>way it is used currently.
>
>> On ARMv7, if SCRLR.A is 0, unaligned access is OK. Here is the description comes from ARM(r) Architecture Reference
>> Manual ARMv7-A and ARMv7-R edition :
>>
><snip>
>
>Could you *please* stop quoting the ARM ARM at us? People who are
>seeking detailed information like that will know where to find it.
>
>--
>Ard.
Thanks for Ard Biesheuvel's review.
Using get_unaligned does not give us too much benefit, and get_unaligned may have some problem.
So it may be better to not use get_unaligned.
next prev parent reply other threads:[~2018-01-16 8:39 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-11 8:22 [PATCH 00/11] KASan for arm Abbott Liu
2017-10-11 8:22 ` [PATCH 01/11] Initialize the mapping of KASan shadow memory Abbott Liu
2017-10-11 19:39 ` Florian Fainelli
2017-10-11 21:41 ` Russell King - ARM Linux
2017-10-17 13:28 ` Liuwenliang (Lamb)
2017-10-11 23:42 ` Dmitry Osipenko
2017-10-19 6:52 ` Liuwenliang (Lamb)
2017-10-19 12:01 ` Russell King - ARM Linux
2017-10-12 7:58 ` Marc Zyngier
2017-11-09 7:46 ` Liuwenliang (Abbott Liu)
2017-11-09 10:10 ` Marc Zyngier
2017-11-15 10:20 ` Liuwenliang (Abbott Liu)
2017-11-15 10:35 ` Marc Zyngier
2017-11-15 13:16 ` Liuwenliang (Abbott Liu)
2017-11-15 13:54 ` Marc Zyngier
2017-11-16 3:07 ` Liuwenliang (Abbott Liu)
2017-11-16 9:54 ` Marc Zyngier
2017-11-16 14:24 ` Liuwenliang (Abbott Liu)
2017-11-16 14:40 ` Marc Zyngier
2017-11-17 1:39 ` 答复: " Liuwenliang (Abbott Liu)
2017-11-17 7:18 ` Liuwenliang (Abbott Liu)
2017-11-17 7:35 ` Christoffer Dall
2017-11-18 10:40 ` Liuwenliang (Abbott Liu)
2017-11-18 13:48 ` Marc Zyngier
[not found] ` <B8AC3E80E903784988AB3003E3E97330C0068F12@dggemm510-mbx.china.huawei.com>
2017-11-21 9:40 ` 答复: " Russell King - ARM Linux
2017-11-21 9:46 ` Marc Zyngier
2017-11-21 12:29 ` Mark Rutland
2017-11-22 12:56 ` Liuwenliang (Abbott Liu)
2017-11-22 13:06 ` Marc Zyngier
2017-11-23 1:54 ` Liuwenliang (Abbott Liu)
2017-11-23 15:22 ` Russell King - ARM Linux
2017-11-27 1:23 ` Liuwenliang (Abbott Liu)
2017-11-23 15:31 ` Mark Rutland
2017-10-19 11:09 ` Russell King - ARM Linux
2018-02-24 14:28 ` Liuwenliang (Abbott Liu)
2017-10-11 8:22 ` [PATCH 02/11] replace memory function Abbott Liu
2017-10-19 12:05 ` Russell King - ARM Linux
2017-10-11 8:22 ` [PATCH 03/11] arm: Kconfig: enable KASan Abbott Liu
2017-10-11 19:15 ` Florian Fainelli
2017-10-19 12:34 ` Russell King - ARM Linux
2017-10-22 12:27 ` Liuwenliang (Lamb)
2017-10-11 8:22 ` [PATCH 04/11] Define the virtual space of KASan's shadow region Abbott Liu
2017-10-14 11:41 ` kbuild test robot
2017-10-16 11:42 ` Liuwenliang (Lamb)
2017-10-16 12:14 ` Ard Biesheuvel
2017-10-17 11:27 ` Liuwenliang (Lamb)
2017-10-17 11:52 ` Ard Biesheuvel
2017-10-17 13:02 ` Liuwenliang (Lamb)
2017-10-19 12:43 ` Russell King - ARM Linux
2017-10-22 12:12 ` Liuwenliang (Lamb)
2017-10-19 12:41 ` Russell King - ARM Linux
2017-10-19 12:40 ` Russell King - ARM Linux
2017-10-11 8:22 ` [PATCH 05/11] Disable kasan's instrumentation Abbott Liu
2017-10-11 19:16 ` Florian Fainelli
2017-10-19 12:47 ` Russell King - ARM Linux
2017-11-15 10:19 ` Liuwenliang (Abbott Liu)
2017-10-11 8:22 ` [PATCH 06/11] change memory_is_poisoned_16 for aligned error Abbott Liu
2017-10-11 23:23 ` Andrew Morton
2017-10-12 7:16 ` Dmitry Vyukov
2017-10-12 11:27 ` Liuwenliang (Lamb)
2017-10-19 12:51 ` Russell King - ARM Linux
2017-12-05 14:19 ` Liuwenliang (Abbott Liu)
2017-12-05 17:08 ` Ard Biesheuvel
2018-01-16 8:39 ` Liuwenliang (Abbott Liu) [this message]
2017-10-11 8:22 ` [PATCH 07/11] Avoid cleaning the KASan shadow area's mapping table Abbott Liu
2017-10-11 8:22 ` [PATCH 08/11] Add support arm LPAE Abbott Liu
2017-10-11 8:22 ` [PATCH 09/11] Don't need to map the shadow of KASan's shadow memory Abbott Liu
2017-10-19 12:55 ` Russell King - ARM Linux
2017-10-22 12:31 ` Liuwenliang (Lamb)
2017-10-11 8:22 ` [PATCH 10/11] Change mapping of kasan_zero_page int readonly Abbott Liu
2017-10-11 19:19 ` Florian Fainelli
2017-10-11 8:22 ` [PATCH 11/11] Add KASan layout Abbott Liu
2017-10-11 19:13 ` [PATCH 00/11] KASan for arm Florian Fainelli
2017-10-11 19:50 ` Florian Fainelli
2017-10-11 21:36 ` Florian Fainelli
2017-10-11 22:10 ` Laura Abbott
2017-10-11 22:58 ` Russell King - ARM Linux
2017-10-17 12:41 ` Liuwenliang (Lamb)
2017-10-12 4:55 ` Liuwenliang (Lamb)
2017-10-12 7:38 ` Arnd Bergmann
2017-10-17 1:04 ` 答复: " Liuwenliang (Lamb)
2018-02-13 18:40 ` Florian Fainelli
2018-02-23 2:10 ` Liuwenliang (Abbott Liu)
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