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X-MS-Exchange-CrossTenant-Id: 3bc2b170-fd94-476d-b0ce-4229bdc904a7 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: zaX/HZpGs9QVxC4q6h0i4vHFoKRIafkRbZACwZM3jRRM6dBgRUSfbqxOD1UZFPBWE+L1cMCna7iKAZn2umsSTq1Sj2y4mavaKyibUd5Uh6M= X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR01MB6865 On 9/24/25 5:41 AM, Qun-wei Lin (林群崴) wrote: > On Fri, 2025-09-05 at 15:30 +0100, Ada Couprie Diaz wrote: >> External email : Please do not click links or open attachments until >> you have verified the sender or the content. >> >> >> Hi, >> >> On 04/08/2025 15:03, Qun-wei Lin (林群崴) wrote: >>> Hi, >>> >>> We have encountered a kernel panic on arm64 when loading modules >>> with >>> both KASAN and KASLR enabled. >>> >>> Kernel version: >>> 6.12 >>> (also reproducible on 6.6-based Android common kernel) >>> >>> Config: >>> CONFIG_KASAN=y >>> CONFIG_KASAN_GENERIC=y >>> CONFIG_KASAN_VMALLOC=y >>> CONFIG_RANDOMIZE_BASE=y >>> # CONFIG_RANDOMIZE_MODULE_REGION_FULL is not set >>> >>> Reproducible: >>> ~50% of the time, when loading any module with Generic KASAN + >>> KASLR >>> enabled. >>> >>> The kernel panic log is as follows: >>> [...] >>> Comm:kworker/4:1 Tainted: G          OE      6.12.23-android16-5- >>> g1e57f0e5996f-4k #1 eee834a579887c0f97d696d30c786233f4fbfcdf >>> [...] >>> >>> If I disable KASLR, the issue does not occur. >> With the context provided I was not able to reproduce the issue >> when testing defconfig + generic KASAN on the following kernels : >> - v6.17-rc4 >> - v6.12.23 Upstream >> - v6.12.23 Android[0] >> - v6.12.23 Upstream, compiled with LLVM >> - v6.12.23 Android[0], compiled with LLVM >> >> (I tried to match the version that appears in your trace) >> >> I tested on both QEMU/KVM and hardware (AMD Seattle), by loading >> and unloading an out-of-tree kernel module repeatedly (an APFS >> driver[1]), >> with no issues on either for all tested kernels. >>> We are not certain which specific patch introduced this issue, but >>> we >>> have confirmed that it does not occur on the Android common kernel >>> 6.1 >>> The problem was first observed after upgrading to 6.6-based >>> kernels. >>> >>> Any suggestions or guidance would be appreciated. >>> Thank you. >> There's not much information to go off of here, my questions would be >> : >> - Are you able to reproduce on an upstream kernel ? >>    (Be it from kernel.org or a "base" Android kernel, like [0]) >> - Are you able to reproduce under publicly available emulators ? >> - Are you able to reproduce with specific, public modules ? >>    (Something available in Debian[2] for example) >> - Which compiler and version are you using ? >> >> It is a bit of work, I'm aware, but given I didn't manage to >> reproduce >> the issue, it would be useful to have as much info on the context >> so either we might be able to reproduce, or you might be able to >> pinpoint the source on your side a bit better ! >> >> I have not seen any other reports since yours, nor did I see any >> patch/fix >> that seemed relevant, so I don't have much more to suggest sadly ; >> others might. >>> Best Regards, >>> >>> >>> 林群崴 (Qun-wei Lin) >>> Qun-wei.Lin@mediatek.com >> Thanks in advance, >> Best regards >> Ada >> >> >> [0]: >> https://urldefense.com/v3/__https://android.googlesource.com/kernel/common/*/refs/tags/android16-6.12-2025-06_r5__;Kw!!CTRNKA9wMg0ARbw!jdaUX7F85FvZJqXX3Uhv5JtUbBtVS1J1KG-WY6odDcKfDjgJEGyCTDMUIN1DVh8uTJn0-ve1n2EjTAA11nsLXit1tcia$ >> [1]: >> https://urldefense.com/v3/__https://github.com/linux-apfs/linux-apfs-rw/__;!!CTRNKA9wMg0ARbw!jdaUX7F85FvZJqXX3Uhv5JtUbBtVS1J1KG-WY6odDcKfDjgJEGyCTDMUIN1DVh8uTJn0-ve1n2EjTAA11nsLXmUUvNiw$ >> [2]: >> https://urldefense.com/v3/__https://packages.debian.org/search?keywords=-dkms&searchon=names&suite=trixie§ion=all__;!!CTRNKA9wMg0ARbw!jdaUX7F85FvZJqXX3Uhv5JtUbBtVS1J1KG-WY6odDcKfDjgJEGyCTDMUIN1DVh8uTJn0-ve1n2EjTAA11nsLXkz_teg4$ >> > > Hi Ada, > > We have root-caused this. > > The issue is caused by an unmapped gap in the arm64 kernel segment, > into which module allocations occasionally land. > > 1. map_kernel() leaves [_text, _stext) unmapped [0], so this gap is > still available for __vmalloc_node_range. > 2. Generic KASAN initializes shadow starting at KERNEL_START (= _text), > so it creates shadow for that unmapped gap using early memblock pages > (PageReserved) [1]. > 3. The module execmem region is about ~128MB; the kernel image sits > inside that region. This means execmem_alloc() can return a VA within > [_text, _stext). > 4. __purge_vmap_area_lazy() depopulate the shadow (reserved pages), > triggering the BUG. > > KASLR is not the root cause, but it increases the hit probability. > > I was able to reproduce this issue on upstream kernel (Linux 6.17.0- > rc7) with QEMU (version 5.2.0 (Debian 1:5.2+dfsg-9ubuntu3.3)). > The key is to ensure we allocate the execmem into the [_text, _stext) > hole and then trigger __purge_vmap_area_lazy(). > > Reproduce the problem: > 1. Temporarily hardcode execmem_arch_setup() to set module_direct_base > =_text, so module allocations fall into the hole. > 2. CONFIG_DEBUG_VM=y is also required to make the error report visible. > 3. Then insmod & rmmod (any .ko file) will trigger the problem. > > I plan to send a patch to exclude [_text, _stext) from > kasan_init_shadow(). In our testing, this fix the issue. I think this has been fixed by this patch: https://lore.kernel.org/linux-arm-kernel/93a6f8e47cce118493e250b719a927f517be12cf.1758316750.git.osandov@osandov.com/ Will already applied it to -next tree AFAIK. Thanks, Yang > > > Thanks! > Qun-wei > > > [0]:https://github.com/torvalds/linux/blob/master/arch/arm64/kernel/pi/map_kernel.c#L81 > [1]:https://github.com/torvalds/linux/blob/master/arch/arm64/mm/kasan_init.c#L309 > > >