Re: [PATCH v8 00/14] kasan: x86: arm64: KASAN tag-based mode for x86

["Maciej Wieczór-Retman" <m.wieczorretman@pm.me>]

On 2026-01-12 at 10:29:57 -0800, Andrew Morton wrote:
>On Mon, 12 Jan 2026 17:26:29 +0000 Maciej Wieczor-Retman <m.wieczorretman@pm.me> wrote:
>
>> The patchset aims to add a KASAN tag-based mode for the x86 architecture
>> with the help of the new CPU feature called Linear Address Masking
>> (LAM). Main improvement introduced by the series is 2x lower memory
>> usage compared to KASAN's generic mode, the only currently available
>> mode on x86. The tag based mode may also find errors that the generic
>> mode couldn't because of differences in how these modes operate.
>
>Well this is a hearty mixture of arm, x86 and MM.  I guess that means
>mm.git.
>
>The review process seems to be proceeding OK so I'll add this to
>mm.git's mm-new branch, which is not included in linux-next.  I'll aim
>to hold it there for a week while people check the patches over and
>send out their acks (please).  Then I hope I can move it into mm.git's
>mm-unstable branch where it will receive linux-next exposure.

Thank you :)

>
>> [1] Currently inline mode doesn't work on x86 due to things missing in
>> the compiler. I have written a patch for clang that seems to fix the
>> inline mode and I was able to boot and check that all patches regarding
>> the inline mode work as expected. My hope is to post the patch to LLVM
>> once this series is completed, and then make inline mode available in
>> the kernel config.
>>
>> [2] While I was able to boot the inline tag-based kernel with my
>> compiler changes in a simulated environment, due to toolchain
>> difficulties I couldn't get it to boot on the machine I had access to.
>> Also boot time results from the simulation seem too good to be true, and
>> they're much too worse for the generic case to be believable. Therefore
>> I'm posting only results from the physical server platform.
>>
>> ======= Compilation
>> Clang was used to compile the series (make LLVM=1) since gcc doesn't
>> seem to have support for KASAN tag-based compiler instrumentation on
>> x86.
>
>OK, known issues and they are understandable.  With this patchset is
>there any way in which our testers can encounter these things?  If so
>can we make changes to protect them from hitting known issues?

The gcc documentation states that the -fsanitize=kernel-hwaddress is
similar to -fsanitize=hwaddress, which only works on AArch64. So that
hints that it shouldn't work.

But while with KASAN sw_tags enabled the kernel compiles fine with gcc,
at least in my patched qemu it doesn't run. I remember Ada Couprie Diaz
mention that passing -march=arrowlake might help since the tag support
seems to be based on arch.

I'll check if there's a non-hacky way to have gcc work too, but perhaps
to minimize hitting known issue, for now HAVE_ARCH_KASAN_SW_TAGS should
be locked behind both ADDRESS_MASKING and CC_IS_CLANG in the Kconfig?

-- 
Kind regards
Maciej Wieczór-Retman