From: Yunseong Kim <ysk@kzalloc.com>
To: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>, James Morse <james.morse@arm.com>,
Yeoreum Yun <yeoreum.yun@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Marc Zyngier <maz@kernel.org>, Mark Brown <broonie@kernel.org>,
Oliver Upton <oliver.upton@linux.dev>,
Ard Biesheuvel <ardb@kernel.org>,
Andrey Ryabinin <ryabinin.a.a@gmail.com>,
Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com
Subject: Re: [PATCH] arm64: cpufeature: Don't cpu_enable_mte() when KASAN_GENERIC is active
Date: Thu, 9 Oct 2025 07:28:19 +0900 [thread overview]
Message-ID: <d0fc7dd9-d921-4d82-9b70-bedca7056961@kzalloc.com> (raw)
In-Reply-To: <CA+fCnZcknrhCOskgLLcTn_-o5jSiQsFni7ihMWuc1Qsd-Pu7gg@mail.gmail.com>
Hi Andrey,
On 10/9/25 6:36 AM, Andrey Konovalov wrote:
> On Wed, Oct 8, 2025 at 11:13 PM Yunseong Kim <ysk@kzalloc.com> wrote:
>> [...]
> I do not understand this. Why is Generic KASAN incompatible with MTE?
My board wouldn't boot on the debian debug kernel, so I enabled
earlycon=pl011,0x40d0000 and checked via the UART console.
> Running Generic KASAN in the kernel while having MTE enabled (and e.g.
> used in userspace) seems like a valid combination.
Then it must be caused by something else. Thank you for letting me know.
It seems to be occurring in the call path as follows:
cpu_enable_mte()
-> try_page_mte_tagging(ZERO_PAGE(0))
-> VM_WARN_ON_ONCE(folio_test_hugetlb(page_folio(page)));
https://elixir.bootlin.com/linux/v6.17/source/arch/arm64/include/asm/mte.h#L83
> The crash log above looks like a NULL-ptr-deref. On which line of code
> does it happen?
Decoded stack trace here:
[ 0.000000] Unable to handle kernel paging request at virtual address dfff800000000005
[ 0.000000] KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
[ 0.000000] Mem abort info:
[ 0.000000] ESR = 0x0000000096000005
[ 0.000000] EC = 0x25: DABT (current EL), IL = 32 bits
[ 0.000000] SET = 0, FnV = 0
[ 0.000000] EA = 0, S1PTW = 0
[ 0.000000] FSC = 0x05: level 1 translation fault
[ 0.000000] Data abort info:
[ 0.000000] ISV = 0, ISS = 0x00000005, ISS2 = 0x00000000
[ 0.000000] CM = 0, WnR = 0, TnD = 0, TagAccess = 0
[ 0.000000] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[ 0.000000] [dfff800000000005] address between user and kernel address ranges
[ 0.000000] Internal error: Oops: 0000000096000005 [#1] SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 6.17+unreleased-debug-arm64 #1 PREEMPTLAZY Debian 6.17-1~exp1
[ 0.000000] pstate: 800000c9 (Nzcv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ 0.000000] pc : cpu_enable_mte (debian/build/build_arm64_none_debug-arm64/include/linux/page-flags.h:1065 (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/include/asm/mte.h:83 (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:2419 (discriminator 1))
[ 0.000000] lr : cpu_enable_mte (debian/build/build_arm64_none_debug-arm64/include/linux/page-flags.h:1065 (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/include/asm/mte.h:83 (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:2419 (discriminator 1))
[ 0.000000] sp : ffff800084f67d80
[ 0.000000] x29: ffff800084f67d80 x28: 0000000000000043 x27: 0000000000000001
[ 0.000000] x26: 0000000000000001 x25: ffff800084204008 x24: ffff800084203da8
[ 0.000000] x23: ffff800084204000 x22: ffff800084203000 x21: ffff8000865a8000
[ 0.000000] x20: fffffffffffffffe x19: fffffdffddaa6a00 x18: 0000000000000011
[ 0.000000] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
[ 0.000000] x14: 0000000000000000 x13: 0000000000000001 x12: ffff700010a04829
[ 0.000000] x11: 1ffff00010a04828 x10: ffff700010a04828 x9 : dfff800000000000
[ 0.000000] x8 : ffff800085024143 x7 : 0000000000000001 x6 : ffff700010a04828
[ 0.000000] x5 : ffff800084f9d200 x4 : 0000000000000000 x3 : ffff8000800794ac
[ 0.000000] x2 : 0000000000000005 x1 : dfff800000000000 x0 : 000000000000002e
[ 0.000000] Call trace:
[ 0.000000] cpu_enable_mte (debian/build/build_arm64_none_debug-arm64/√ (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/include/asm/mte.h:83 (discriminator 1) debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:2419 (discriminator 1)) (P)
[ 0.000000] enable_cpu_capabilities (debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:3561 (discriminator 2))
[ 0.000000] setup_boot_cpu_features (debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:3888 debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/cpufeature.c:3906)
[ 0.000000] smp_prepare_boot_cpu (debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/smp.c:466)
[ 0.000000] start_kernel (debian/build/build_arm64_none_debug-arm64/init/main.c:929)
[ 0.000000] __primary_switched (debian/build/build_arm64_none_debug-arm64/arch/arm64/kernel/head.S:247)
[ 0.000000] Code: 9100c280 d2d00001 f2fbffe1 d343fc02 (38e16841)
All code
========
0: 9100c280 add x0, x20, #0x30
4: d2d00001 mov x1, #0x800000000000 // #140737488355328
8: f2fbffe1 movk x1, #0xdfff, lsl #48
c: d343fc02 lsr x2, x0, #3
10:* 38e16841 ldrsb w1, [x2, x1] <-- trapping instruction
Code starting with the faulting instruction
===========================================
0: 38e16841 ldrsb w1, [x2, x1]
[ 0.000000] ---[ end trace 0000000000000000 ]---
[ 0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[ 0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
If there are any other points you'd like me to check or directions, please
let me know.
Thank you!
Yunseong
next prev parent reply other threads:[~2025-10-08 22:28 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-08 21:04 [PATCH] arm64: cpufeature: Don't cpu_enable_mte() when KASAN_GENERIC is active Yunseong Kim
2025-10-08 21:36 ` Andrey Konovalov
2025-10-08 22:28 ` Yunseong Kim [this message]
2025-10-08 23:10 ` Yunseong Kim
2025-10-10 12:29 ` Will Deacon
2025-10-10 14:56 ` Yunseong Kim
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d0fc7dd9-d921-4d82-9b70-bedca7056961@kzalloc.com \
--to=ysk@kzalloc.com \
--cc=andreyknvl@gmail.com \
--cc=ardb@kernel.org \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=dvyukov@google.com \
--cc=glider@google.com \
--cc=james.morse@arm.com \
--cc=kasan-dev@googlegroups.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maz@kernel.org \
--cc=oliver.upton@linux.dev \
--cc=ryabinin.a.a@gmail.com \
--cc=vincenzo.frascino@arm.com \
--cc=will@kernel.org \
--cc=yeoreum.yun@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox