linux-kernel - Re: [PATCH v2 13/14] x86: runtime_const used for KASAN_SHADOW

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Message-ID: <CA+fCnZdunJhoNgsQMm4cPyephj9L7sMq-YF9sE7ANk0e7h7d=Q@mail.gmail.com>
Date: Fri, 21 Mar 2025 21:16:12 +0100
From: Andrey Konovalov <andreyknvl@...il.com>
To: Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>
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Subject: Re: [PATCH v2 13/14] x86: runtime_const used for KASAN_SHADOW_END

On Fri, Mar 21, 2025 at 8:21 PM Maciej Wieczor-Retman
<maciej.wieczor-retman@...el.com> 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