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SubjectRe: [PATCH] arm64: mm: reset address tag set by kasan sw tagging
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Hi Catalin,


On 6/10/2020 5:06 PM, Catalin Marinas wrote:
> On Wed, Jun 10, 2020 at 04:39:44PM +0530, Shyam Thombre wrote:
>> KASAN sw tagging sets a random tag of 8 bits in the top byte of the pointer
>> returned by the memory allocating functions. So for the functions unaware
>> of this change, the top 8 bits of the address must be reset which is done
>> by the function arch_kasan_reset_tag().
>>
>> Signed-off-by: Shyam Thombre <sthombre@codeaurora.org>
>> ---
>> arch/arm64/mm/mmu.c | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index e7fbc62..eae7655 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -723,6 +723,7 @@ int kern_addr_valid(unsigned long addr)
>> pmd_t *pmdp, pmd;
>> pte_t *ptep, pte;
>>
>> + addr = arch_kasan_reset_tag(addr);
>> if ((((long)addr) >> VA_BITS) != -1UL)
>> return 0;
>
> It would be interesting to know what fails without this patch. The only
> user seems to be read_kcore() and, at a quick look, I don't see how it
> can generate tagged addresses.
>

This issue is seen in downstream GPU drivers. It currently doesn't look
to impact any upstream users.


--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

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