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Message-ID: <2b8e3ca5-1645-489c-9d7f-dd13e5fc43ed@kzalloc.com>
Date: Thu, 9 Oct 2025 08:10:53 +0900
From: Yunseong Kim <ysk@...lloc.com>
To: Catalin Marinas <catalin.marinas@....com>,
James Morse <james.morse@....com>, Will Deacon <will@...nel.org>,
Yeoreum Yun <yeoreum.yun@....com>,
Vincenzo Frascino <vincenzo.frascino@....com>
Cc: Andrey Konovalov <andreyknvl@...il.com>, Marc Zyngier <maz@...nel.org>,
Mark Brown <broonie@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
Ard Biesheuvel <ardb@...nel.org>, Andrey Ryabinin <ryabinin.a.a@...il.com>,
Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
kasan-dev@...glegroups.com
Subject: Re: [PATCH] arm64: cpufeature: Don't cpu_enable_mte() when
KASAN_GENERIC is active
To summarize my situation, I thought the boot panic issue might be due
to incompatibility between MTE and KASAN Generic, so I sent this patch.
However, it seems that the problem is related to the call path involving
ZERO page. Also, I am curious how it works correctly in other machine.
On 10/9/25 7:28 AM, Yunseong Kim wrote:
> Hi Andrey,
>
> On 10/9/25 6:36 AM, Andrey Konovalov wrote:
>> On Wed, Oct 8, 2025 at 11:13 PM Yunseong Kim <ysk@...lloc.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
-> page_folio(ZERO_PAGE(0))
-> (struct folio *)_compound_head(ZERO_PAGE(0))
https://elixir.bootlin.com/linux/v6.17/source/include/linux/page-flags.h#L307
>> 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
Best regards,
Yunseong
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