[syzbot] [kernel?] KASAN: unknown-crash Read in copy_mc_to_kernel

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3a8660878839 Linux 6.18-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10109542580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9ad7b090a18654a7
dashboard link: https://syzkaller.appspot.com/bug?extid=d155b4893773c196cdd9
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b39e59492185/disk-3a866087.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a9f71abd3189/vmlinux-3a866087.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a8ee0fb986c2/bzImage-3a866087.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d155b4...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: unknown-crash in instrument_memcpy_before include/linux/instrumented.h:163 [inline]
BUG: KASAN: unknown-crash in copy_mc_to_kernel+0x35/0xb0 arch/x86/lib/copy_mc.c:74
Read of size 4096 at addr ffff8880af860000 by task syz.5.1091/9436

CPU: 1 UID: 0 PID: 9436 Comm: syz.5.1091 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:200
instrument_memcpy_before include/linux/instrumented.h:163 [inline]
copy_mc_to_kernel+0x35/0xb0 arch/x86/lib/copy_mc.c:74
dump_page_copy fs/coredump.c:1321 [inline]
dump_user_range+0x2e4/0xc90 fs/coredump.c:1372
elf_core_dump+0x3369/0x3960 fs/binfmt_elf.c:2111
coredump_write+0x116c/0x1900 fs/coredump.c:1049
vfs_coredump+0x1db5/0x2a60 fs/coredump.c:1170
get_signal+0x1108/0x1340 kernel/signal.c:3019
arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:40 [inline]
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
irqentry_exit_to_user_mode+0x7e/0x110 kernel/entry/common.c:73
exc_page_fault+0xab/0x100 arch/x86/mm/fault.c:1535
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7f97dd38eed1
Code: 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 48 3d 01 f0 ff ff 73 01 <c3> 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f
RSP: 002b:00000000fffffd10 EFLAGS: 00010217
RAX: 0000000000000000 RBX: 00007f97dd5e6090 RCX: 00007f97dd38eec9
RDX: 0000000000000000 RSI: 00000000fffffd10 RDI: 0000000001000000
RBP: 00007f97dd411f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007f97dd5e6128 R14: 00007f97dd5e6090 R15: 00007ffcef26f528
</TASK>

The buggy address belongs to the physical page:
page: refcount:3 mapcount:1 mapping:ffff888064726de8 index:0x14f pfn:0xaf860
memcg:ffff88801aea1a00
aops:ext4_da_aops ino:7f0 dentry name(?):"syz.IuCCpi"
flags: 0xfff6800000002c(referenced|uptodate|lru|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff6800000002c ffffea0002c0b3c8 ffffea0002be1848 ffff888064726de8
raw: 000000000000014f 0000000000000000 0000000300000000 ffff88801aea1a00
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Movable, gfp_mask 0x152c4a(GFP_NOFS|__GFP_HIGHMEM|__GFP_MOVABLE|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 7122, tgid 7122 (syz.3.435), ts 155471149983, free_ts 153032620682
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
prep_new_page mm/page_alloc.c:1858 [inline]
get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_frozen_pages_noprof mm/mempolicy.c:2487 [inline]
alloc_pages_noprof+0xa9/0x190 mm/mempolicy.c:2507
folio_alloc_noprof+0x1e/0x30 mm/mempolicy.c:2517
filemap_alloc_folio_noprof+0xdf/0x470 mm/filemap.c:1020
ractl_alloc_folio mm/readahead.c:189 [inline]
page_cache_ra_unbounded+0x35d/0x9a0 mm/readahead.c:275
do_async_mmap_readahead mm/filemap.c:3376 [inline]
filemap_fault+0x62d/0x12b0 mm/filemap.c:3475
__do_fault+0x138/0x390 mm/memory.c:5280
do_read_fault mm/memory.c:5698 [inline]
do_fault mm/memory.c:5832 [inline]
do_pte_missing mm/memory.c:4361 [inline]
handle_pte_fault mm/memory.c:6177 [inline]
__handle_mm_fault+0x35e3/0x5400 mm/memory.c:6318
handle_mm_fault+0x40a/0x8e0 mm/memory.c:6487
faultin_page mm/gup.c:1126 [inline]
__get_user_pages+0x165c/0x2a00 mm/gup.c:1428
__get_user_pages_locked mm/gup.c:1692 [inline]
get_dump_page+0x1ac/0x3f0 mm/gup.c:2192
dump_user_range+0x1de/0xc90 fs/coredump.c:1366
elf_core_dump+0x3369/0x3960 fs/binfmt_elf.c:2111
page last free pid 7072 tgid 7068 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1394 [inline]
free_unref_folios+0xdb3/0x14f0 mm/page_alloc.c:2963
folios_put_refs+0x584/0x670 mm/swap.c:1002
folio_batch_release include/linux/pagevec.h:101 [inline]
shmem_undo_range+0x49e/0x14b0 mm/shmem.c:1120
shmem_truncate_range mm/shmem.c:1232 [inline]
shmem_evict_inode+0x272/0xa70 mm/shmem.c:1360
evict+0x504/0x9c0 fs/inode.c:810
__dentry_kill+0x209/0x660 fs/dcache.c:669
dput+0x19f/0x2b0 fs/dcache.c:911
__fput+0x68e/0xa70 fs/file_table.c:476
task_work_run+0x1d4/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x2300 kernel/exit.c:966
do_group_exit+0x21c/0x2d0 kernel/exit.c:1107
get_signal+0x1285/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0xa0/0x790 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x72/0x130 kernel/entry/common.c:40
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
do_syscall_64+0x2bd/0xfa0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff8880af85ff00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
ffff8880af85ff80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff8880af860000: 00 c9 2b 58 80 88 ff ff 00 00 00 00 00 00 00 00
^
ffff8880af860080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8880af860100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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