From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
Andrey Konovalov <andreyknvl@google.com>
Cc: linux-arm-kernel@lists.infradead.org,
Marco Elver <elver@google.com>,
Elena Petrova <lenaptr@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Will Deacon <will.deacon@arm.com>,
Branislav Rankov <Branislav.Rankov@arm.com>,
kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Andrew Morton <akpm@linux-foundation.org>,
Evgenii Stepanov <eugenis@google.com>
Subject: Re: [PATCH 20/35] arm64: mte: Add in-kernel MTE helpers
Date: Thu, 27 Aug 2020 11:31:56 +0100 [thread overview]
Message-ID: <588f3812-c9d0-8dbe-fce2-1ea89f558bd2@arm.com> (raw)
In-Reply-To: <20200827093808.GB29264@gaia>
Hi Catalin,
On 8/27/20 10:38 AM, Catalin Marinas wrote:
> On Fri, Aug 14, 2020 at 07:27:02PM +0200, Andrey Konovalov wrote:
>> diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
>> index 1c99fcadb58c..733be1cb5c95 100644
>> --- a/arch/arm64/include/asm/mte.h
>> +++ b/arch/arm64/include/asm/mte.h
>> @@ -5,14 +5,19 @@
>> #ifndef __ASM_MTE_H
>> #define __ASM_MTE_H
>>
>> -#define MTE_GRANULE_SIZE UL(16)
>> +#include <asm/mte_asm.h>
>
> So the reason for this move is to include it in asm/cache.h. Fine by
> me but...
>
>> #define MTE_GRANULE_MASK (~(MTE_GRANULE_SIZE - 1))
>> #define MTE_TAG_SHIFT 56
>> #define MTE_TAG_SIZE 4
>> +#define MTE_TAG_MASK GENMASK((MTE_TAG_SHIFT + (MTE_TAG_SIZE - 1)), MTE_TAG_SHIFT)
>> +#define MTE_TAG_MAX (MTE_TAG_MASK >> MTE_TAG_SHIFT)
>
> ... I'd rather move all these definitions in a file with a more
> meaningful name like mte-def.h. The _asm implies being meant for .S
> files inclusion which isn't the case.
>
mte-asm.h was originally called mte_helper.h hence it made sense to have these
defines here. But I agree with your proposal it makes things more readable and
it is in line with the rest of the arm64 code (e.g. page-def.h).
We should as well update the commit message accordingly.
>> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
>> index eb39504e390a..e2d708b4583d 100644
>> --- a/arch/arm64/kernel/mte.c
>> +++ b/arch/arm64/kernel/mte.c
>> @@ -72,6 +74,47 @@ int memcmp_pages(struct page *page1, struct page *page2)
>> return ret;
>> }
>>
>> +u8 mte_get_mem_tag(void *addr)
>> +{
>> + if (system_supports_mte())
>> + addr = mte_assign_valid_ptr_tag(addr);
>
> The mte_assign_valid_ptr_tag() is slightly misleading. All it does is
> read the allocation tag from memory.
>
> I also think this should be inline asm, possibly using alternatives.
> It's just an LDG instruction (and it saves us from having to invent a
> better function name).
>
Yes, I agree, I implemented this code in the early days and never got around to
refactor it.
>> +
>> + return 0xF0 | mte_get_ptr_tag(addr);
>> +}
>> +
>> +u8 mte_get_random_tag(void)
>> +{
>> + u8 tag = 0xF;
>> +
>> + if (system_supports_mte())
>> + tag = mte_get_ptr_tag(mte_assign_random_ptr_tag(NULL));
>
> Another alternative inline asm with an IRG instruction.
>
As per above.
>> +
>> + return 0xF0 | tag;
>> +}
>> +
>> +void * __must_check mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
>> +{
>> + void *ptr = addr;
>> +
>> + if ((!system_supports_mte()) || (size == 0))
>> + return addr;
>> +
>> + tag = 0xF0 | (tag & 0xF);
>> + ptr = (void *)__tag_set(ptr, tag);
>> + size = ALIGN(size, MTE_GRANULE_SIZE);
>
> I think aligning the size is dangerous. Can we instead turn it into a
> WARN_ON if not already aligned? At a quick look, the callers of
> kasan_{un,}poison_memory() already align the size.
>
The size here is used only for tagging purposes and if we want to tag a
subgranule amount of memory we end up tagging the granule anyway. Why do you
think it can be dangerous?
Anyway I agree on the fact that is seems redundant, a WARN_ON here should be
sufficient.
>> +
>> + mte_assign_mem_tag_range(ptr, size);
>> +
>> + /*
>> + * mte_assign_mem_tag_range() can be invoked in a multi-threaded
>> + * context, ensure that tags are written in memory before the
>> + * reference is used.
>> + */
>> + smp_wmb();
>> +
>> + return ptr;
>
> I'm not sure I understand the barrier here. It ensures the relative
> ordering of memory (or tag) accesses on a CPU as observed by other CPUs.
> While the first access here is setting the tag, I can't see what other
> access on _this_ CPU it is ordered with.
>
You are right it can be removed. I was just overthinking here.
>> +}
>> +
>> static void update_sctlr_el1_tcf0(u64 tcf0)
>> {
>> /* ISB required for the kernel uaccess routines */
>> diff --git a/arch/arm64/lib/mte.S b/arch/arm64/lib/mte.S
>> index 03ca6d8b8670..8c743540e32c 100644
>> --- a/arch/arm64/lib/mte.S
>> +++ b/arch/arm64/lib/mte.S
>> @@ -149,3 +149,44 @@ SYM_FUNC_START(mte_restore_page_tags)
>>
>> ret
>> SYM_FUNC_END(mte_restore_page_tags)
>> +
>> +/*
>> + * Assign pointer tag based on the allocation tag
>> + * x0 - source pointer
>> + * Returns:
>> + * x0 - pointer with the correct tag to access memory
>> + */
>> +SYM_FUNC_START(mte_assign_valid_ptr_tag)
>> + ldg x0, [x0]
>> + ret
>> +SYM_FUNC_END(mte_assign_valid_ptr_tag)
>> +
>> +/*
>> + * Assign random pointer tag
>> + * x0 - source pointer
>> + * Returns:
>> + * x0 - pointer with a random tag
>> + */
>> +SYM_FUNC_START(mte_assign_random_ptr_tag)
>> + irg x0, x0
>> + ret
>> +SYM_FUNC_END(mte_assign_random_ptr_tag)
>
> As I said above, these two can be inline asm.
>
Agreed.
>> +
>> +/*
>> + * Assign allocation tags for a region of memory based on the pointer tag
>> + * x0 - source pointer
>> + * x1 - size
>> + *
>> + * Note: size is expected to be MTE_GRANULE_SIZE aligned
>> + */
>> +SYM_FUNC_START(mte_assign_mem_tag_range)
>> + /* if (src == NULL) return; */
>> + cbz x0, 2f
>> + /* if (size == 0) return; */
>
> You could skip the cbz here and just document that the size should be
> non-zero and aligned. The caller already takes care of this check.
>
I would prefer to keep the check here, unless there is a valid reason, since
allocate(0) is a viable option hence tag(x, 0) should be as well. The caller
takes care of it in one place, today, but I do not know where the API will be
used in future.
>> + cbz x1, 2f
>> +1: stg x0, [x0]
>> + add x0, x0, #MTE_GRANULE_SIZE
>> + sub x1, x1, #MTE_GRANULE_SIZE
>> + cbnz x1, 1b
>> +2: ret
>> +SYM_FUNC_END(mte_assign_mem_tag_range)
>
--
Regards,
Vincenzo
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next prev parent reply other threads:[~2020-08-27 10:31 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-14 17:26 [PATCH 00/35] kasan: add hardware tag-based mode for arm64 Andrey Konovalov
2020-08-14 17:26 ` [PATCH 01/35] kasan: KASAN_VMALLOC depends on KASAN_GENERIC Andrey Konovalov
2020-08-14 17:26 ` [PATCH 02/35] kasan: group vmalloc code Andrey Konovalov
2020-08-14 17:26 ` [PATCH 03/35] kasan: shadow declarations only for software modes Andrey Konovalov
2020-09-18 14:55 ` Marco Elver
2020-09-18 14:56 ` Andrey Konovalov
2020-08-14 17:26 ` [PATCH 04/35] kasan: rename (un)poison_shadow to (un)poison_memory Andrey Konovalov
2020-08-14 17:26 ` [PATCH 05/35] kasan: rename KASAN_SHADOW_* to KASAN_GRANULE_* Andrey Konovalov
2020-08-14 17:26 ` [PATCH 06/35] kasan: only build init.c for software modes Andrey Konovalov
2020-08-14 17:26 ` [PATCH 07/35] kasan: split out shadow.c from common.c Andrey Konovalov
2020-08-14 17:26 ` [PATCH 08/35] kasan: rename generic/tags_report.c files Andrey Konovalov
2020-08-14 17:26 ` [PATCH 09/35] kasan: don't duplicate config dependencies Andrey Konovalov
2020-08-14 17:26 ` [PATCH 10/35] kasan: hide invalid free check implementation Andrey Konovalov
2020-08-14 17:26 ` [PATCH 11/35] kasan: decode stack frame only with KASAN_STACK_ENABLE Andrey Konovalov
2020-08-14 17:26 ` [PATCH 12/35] kasan, arm64: only init shadow for software modes Andrey Konovalov
2020-08-14 17:26 ` [PATCH 13/35] kasan, arm64: only use kasan_depth " Andrey Konovalov
2020-08-14 17:26 ` [PATCH 14/35] kasan: rename addr_has_shadow to addr_has_metadata Andrey Konovalov
2020-08-14 17:26 ` [PATCH 15/35] kasan: rename print_shadow_for_address to print_memory_metadata Andrey Konovalov
2020-08-14 17:26 ` [PATCH 16/35] kasan: kasan_non_canonical_hook only for software modes Andrey Konovalov
2020-08-14 17:26 ` [PATCH 17/35] kasan: rename SHADOW layout macros to META Andrey Konovalov
2020-08-14 17:27 ` [PATCH 18/35] kasan: separate metadata_fetch_row for each mode Andrey Konovalov
2020-08-14 17:27 ` [PATCH 19/35] kasan: don't allow SW_TAGS with ARM64_MTE Andrey Konovalov
2020-08-27 8:04 ` Catalin Marinas
2020-08-27 9:54 ` Vincenzo Frascino
2020-08-27 12:02 ` Andrey Konovalov
2020-08-14 17:27 ` [PATCH 20/35] arm64: mte: Add in-kernel MTE helpers Andrey Konovalov
2020-08-27 9:38 ` Catalin Marinas
2020-08-27 10:31 ` Vincenzo Frascino [this message]
2020-08-27 11:10 ` Catalin Marinas
2020-08-27 11:24 ` Vincenzo Frascino
2020-08-27 12:46 ` Andrey Konovalov
2020-09-08 13:23 ` Andrey Konovalov
2020-09-08 14:50 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 21/35] arm64: mte: Add in-kernel tag fault handler Andrey Konovalov
2020-08-27 9:54 ` Catalin Marinas
2020-08-27 10:44 ` Vincenzo Frascino
2020-08-27 12:31 ` Andrey Konovalov
2020-08-27 13:10 ` Catalin Marinas
2020-08-27 13:34 ` Andrey Konovalov
2020-08-27 14:56 ` Catalin Marinas
2020-08-27 19:14 ` Evgenii Stepanov
2020-08-28 9:56 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 22/35] arm64: mte: Enable in-kernel MTE Andrey Konovalov
2020-08-27 10:01 ` Catalin Marinas
2020-08-27 10:46 ` Vincenzo Frascino
2020-09-08 14:39 ` Andrey Konovalov
2020-09-08 14:52 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 23/35] arm64: mte: Convert gcr_user into an exclude mask Andrey Konovalov
2020-08-14 17:27 ` [PATCH 24/35] arm64: mte: Switch GCR_EL1 in kernel entry and exit Andrey Konovalov
2020-08-27 10:38 ` Catalin Marinas
2020-08-27 10:56 ` Vincenzo Frascino
2020-08-27 12:16 ` Catalin Marinas
2020-09-08 14:02 ` Andrey Konovalov
2020-09-08 14:53 ` Andrey Konovalov
2020-09-08 15:39 ` Catalin Marinas
2020-09-08 19:41 ` Derrick McKee
2020-09-08 13:58 ` Andrey Konovalov
2020-09-08 15:16 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 25/35] kasan: introduce CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-08-27 11:33 ` Vincenzo Frascino
2020-08-27 12:22 ` Andrey Konovalov
2020-08-14 17:27 ` [PATCH 26/35] kasan, arm64: Enable TBI EL1 Andrey Konovalov
2020-08-27 10:40 ` Catalin Marinas
2020-08-27 11:05 ` Vincenzo Frascino
2020-08-27 11:13 ` Catalin Marinas
2020-08-27 11:17 ` Vincenzo Frascino
2020-08-27 12:43 ` Andrey Konovalov
2020-08-27 13:45 ` Vincenzo Frascino
2020-08-27 14:36 ` Andrey Konovalov
2020-09-08 13:18 ` Andrey Konovalov
2020-09-08 14:06 ` Catalin Marinas
2020-09-08 14:12 ` Andrey Konovalov
2020-09-08 14:41 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 27/35] kasan, arm64: align allocations for HW_TAGS Andrey Konovalov
2020-08-14 17:27 ` [PATCH 28/35] kasan: define KASAN_GRANULE_SIZE " Andrey Konovalov
2020-08-27 10:41 ` Catalin Marinas
2020-08-27 11:07 ` Vincenzo Frascino
2020-08-27 12:05 ` Andrey Konovalov
2020-08-14 17:27 ` [PATCH 29/35] kasan, x86, s390: update undef CONFIG_KASAN Andrey Konovalov
2020-08-14 17:27 ` [PATCH 30/35] kasan, arm64: expand CONFIG_KASAN checks Andrey Konovalov
2020-08-14 17:27 ` [PATCH 31/35] kasan, arm64: implement HW_TAGS runtime Andrey Konovalov
2020-08-27 10:45 ` Catalin Marinas
2020-08-27 11:35 ` Vincenzo Frascino
2020-08-27 12:37 ` Andrey Konovalov
2020-08-14 17:27 ` [PATCH 32/35] kasan, arm64: print report from tag fault handler Andrey Konovalov
2020-08-27 10:48 ` Catalin Marinas
2020-08-27 12:11 ` Vincenzo Frascino
2020-08-27 12:34 ` Andrey Konovalov
2020-08-27 14:21 ` Catalin Marinas
2020-08-14 17:27 ` [PATCH 33/35] kasan, slub: reset tags when accessing metadata Andrey Konovalov
2020-08-14 17:27 ` [PATCH 34/35] kasan, arm64: enable CONFIG_KASAN_HW_TAGS Andrey Konovalov
2020-08-14 17:27 ` [PATCH 35/35] kasan: add documentation for hardware tag-based mode Andrey Konovalov
2020-08-28 11:12 ` Marco Elver
2020-08-28 12:28 ` Andrey Konovalov
2020-09-14 19:06 ` [PATCH 00/35] kasan: add hardware tag-based mode for arm64 Derrick McKee
2020-09-14 20:04 ` Andrey Konovalov
2020-09-14 21:36 ` Derrick McKee
2020-09-14 22:41 ` Derrick McKee
2020-09-14 22:50 ` Andrey Konovalov
2020-09-15 9:46 ` Derrick McKee
2020-09-15 17:51 ` Derrick McKee
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