linux-kernel - Re: [PATCH v2 01/14] kasan: sw_tags: Use arithmetic shift for shadow computation

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Message-ID: <6wdzi5lszeaycdfjjowrbsnniks35zhatavknktskslwop5fne@uv5wzotu4ri4>
Date: Tue, 25 Feb 2025 21:12:57 +0100
From: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
To: Andrey Konovalov <andreyknvl@...il.com>
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Subject: Re: [PATCH v2 01/14] kasan: sw_tags: Use arithmetic shift for shadow
 computation

On 2025-02-25 at 20:12:40 +0100, Maciej Wieczor-Retman wrote:
>On 2025-02-25 at 18:20:08 +0100, Maciej Wieczor-Retman wrote:
>>On 2025-02-22 at 16:06:02 +0100, Andrey Konovalov wrote:
>>>On Fri, Feb 21, 2025 at 2:12 PM Maciej Wieczor-Retman
>>><maciej.wieczor-retman@...el.com> wrote:
>>>> >                   Thus, the possible values a shadow address can
>>>> >take are the result of the memory-to-shadow mapping applied to
>>>> >[0xff00000000000000, 0xffffffffffffffff], not to the whole address
>>>> >space. So we can make this check more precise.
>>>>
>>>> In case my question above didn't lead to this: what happens to the rest of the
>>>> values if they get plugged into kasan_mem_to_shadow()?
>>>
>>>We will get some invalid addresses. But this should never happen in
>>>the first place.
>>
>>Thanks for letting me know about the tag resets, that should make changing the
>>check in kasan_non_canonical_hook() easier.
>
>Ah, but the [0xff00000000000000, 0xffffffffffffffff] won't be true for x86
>right? Here the tag reset function only resets bits 60:57. So I presume
>[0x3e00000000000000, 0xffffffffffffffff] would be the range?

Sorry, brain freeze, I meant [0x1e00000000000000, 0xffffffffffffffff]

-- 
Kind regards
Maciej Wieczór-Retman