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

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Message-ID: <aW6HcGjkAZ3lITeA@wieczorr-mobl1.localdomain>
Date: Mon, 19 Jan 2026 19:43:23 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: corbet@....net, morbo@...gle.com, rppt@...nel.org, lorenzo.stoakes@...cle.com, ubizjak@...il.com, mingo@...hat.com, vincenzo.frascino@....com, maciej.wieczor-retman@...el.com, maz@...nel.org, catalin.marinas@....com, yeoreum.yun@....com, will@...nel.org, jackmanb@...gle.com, samuel.holland@...ive.com, glider@...gle.com, osandov@...com, nsc@...nel.org, luto@...nel.org, jpoimboe@...nel.org, akpm@...ux-foundation.org, Liam.Howlett@...cle.com, kees@...nel.org, jan.kiszka@...mens.com, thomas.lendacky@....com, jeremy.linton@....com, dvyukov@...gle.com, axelrasmussen@...gle.com, leitao@...ian.org, bigeasy@...utronix.de, peterz@...radead.org, mark.rutland@....com, urezki@...il.com, brgerst@...il.com, hpa@...or.com, mhocko@...e.com, andreyknvl@...il.com, weixugc@...gle.com, kbingham@...nel.org, vbabka@...e.cz, nathan@...nel.org, trintaeoitogc@...il.com, samitolvanen@...gle.com, tglx@...nel.org, thuth@...hat.com, surenb@...gle.com, anshuman.khandual@....com, smostafa@...gle.com,
	yuanchu@...gle.com, ada.coupriediaz@....com, dave.hansen@...ux.intel.com, kas@...nel.org, nick.desaulniers+lkml@...il.com, david@...nel.org, bp@...en8.de, ardb@...nel.org, justinstitt@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org, kasan-dev@...glegroups.com, llvm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, linux-kbuild@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v8 00/14] kasan: x86: arm64: KASAN tag-based mode for x86

On 2026-01-19 at 17:33:35 +0100, Andrey Ryabinin wrote:
>On 1/12/26 6:26 PM, Maciej Wieczor-Retman wrote:
>
>> ======= 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.
>>
>
>It appears that GCC nominally supports this, but in practice it does not work.
>Here is a minimal reproducer: https://godbolt.org/z/s85e11T5r
>
>As far as I understand, calling a function through a tagged pointer is not
>supported by the hardware, so GCC attempts to clear the tag before the call.
>This behavior seems to be inherited from the userspace implementation of HWASan (-fsanitize=hwaddress).
>
>I have filed a GCC bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123696
>
>For the kernel, we probably do not want this masking at all, as effectively 99.9–100%
>of function pointer calls are expected to be untagged anyway.
>
>Clang does not appear to do this, not even for userspace.

Cool, thanks, nice to know why the kernel didn't start with gcc.

I'm going to check in on the bug report every now and then and once it gets
resolved I'll test if everything works as expected on both compilers.

-- 
Kind regards
Maciej Wieczór-Retman