Re: [PATCH v2 13/14] x86: runtime_const used for KASAN_SHADOW_END

[Maciej Wieczor-Retman]

On 2025-03-21 at 21:16:12 +0100, Andrey Konovalov wrote:
>On Fri, Mar 21, 2025 at 8:21 PM Maciej Wieczor-Retman
><maciej.wieczor-retman@xxxxxxxxx> wrote:
>>
>> >To account for this, let's then set hwasan-instrument-with-calls=0
>> >when CONFIG_KASAN_INLINE is enabled. And also please add a comment
>> >explaining why this is done.
>>
>> After adding this option the kernel doesn't want to boot past uncompressing :b
>>
>> I went into Samuel's clang PR [1] and found there might be one more LShr that
>> needs changing into AShr [2]? But I'm not very good at clang code. Do you maybe
>> know if anything else in the clang code could be messing things up?
>>
>> After changing that LShr to AShr it moves a little further and hangs on some
>> initmem setup code. Then I thought my KASAN_SHADOW_OFFSET is an issue so I
>> changed to 4-level paging and the offset to 0xfffffc0000000000 and it moves a
>> little further and panics on kmem_cache_init. I'll be debugging that further but
>> just thought I'd ask if you know about something missing from the compiler side?
>>
>> [1] https://github.com/llvm/llvm-project/pull/103727
>> [2] https://github.com/SiFiveHolland/llvm-project/blob/up/hwasan-opt/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp#L995
>
>Hm, I only recall looking at the compiler code when investigating [1].
>But as this series points out, [1] can be considered a feature and not
>a bug. Other than that, nothing comes to mind.
>
>Thanks!
>
>[1] https://bugzilla.kernel.org/show_bug.cgi?id=218043

So I assume that if outline mode works, inline mode should be fine as far as
kernel is concerned? If so perhaps it will be more time efficient to post v3 of
this series (once I'm done with kasan_non_canonical_hook() edge cases and
unpoisoning per-cpu vms[areas] with the same tag) and work on the clang side
later / in the meantime.

-- 
Kind regards
Maciej Wieczór-Retman