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BUG: KASAN: use-after-free in kvm_xen_shared_info_init+0x3c6/0x440 arch/x86/kvm/xen.c:90
Read of size 4 at addr ffff88804c76d900 by task syz.1.860/10182

CPU: 0 UID: 0 PID: 10182 Comm: syz.1.860 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
 kvm_xen_shared_info_init+0x3c6/0x440 arch/x86/kvm/xen.c:90
 kvm_xen_hvm_set_attr+0xcef/0x16a0 arch/x86/kvm/xen.c:806
 kvm_arch_vm_ioctl+0x2a0/0x18d0 arch/x86/kvm/x86.c:7528
 kvm_vm_ioctl+0x1564/0x4050 virt/kvm/kvm_main.c:5380
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f561b59ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f561c375028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f561b816090 RCX: 00007f561b59ce59
RDX: 0000000000000004 RSI: 000000004048aec9 RDI: 0000000000000003
RBP: 00007f561b632d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f561b816128 R14: 00007f561b816090 R15: 00007ffeb97e51d8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x4 pfn:0x4c76d
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea0001499108 ffff8880b84412f0 0000000000000000
raw: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 0, migratetype Movable, gfp_mask 0x140cca(GFP_HIGHUSER_MOVABLE|__GFP_COMP), pid 10182, tgid 10179 (syz.1.860), ts 424112873623, free_ts 424227877438
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1858
 prep_new_page mm/page_alloc.c:1866 [inline]
 get_page_from_freelist+0x11a6/0x33b0 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5226
 alloc_pages_mpol+0x1fb/0x540 mm/mempolicy.c:2490
 folio_alloc_mpol_noprof+0x36/0x260 mm/mempolicy.c:2509
 shmem_alloc_folio+0x135/0x160 mm/shmem.c:1933
 shmem_alloc_and_add_folio+0x371/0xd40 mm/shmem.c:1975
 shmem_get_folio_gfp+0x6ab/0x1900 mm/shmem.c:2564
 shmem_fault+0x1f9/0xa20 mm/shmem.c:2765
 __do_fault+0x10b/0x440 mm/memory.c:5474
 do_shared_fault mm/memory.c:5973 [inline]
 do_fault+0x2db/0x1750 mm/memory.c:6047
 do_pte_missing mm/memory.c:4566 [inline]
 handle_pte_fault mm/memory.c:6427 [inline]
 __handle_mm_fault+0x187d/0x2a00 mm/memory.c:6565
 handle_mm_fault+0x36d/0xa20 mm/memory.c:6734
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0x1178/0x32a0 mm/gup.c:1428
 __get_user_pages_locked mm/gup.c:1692 [inline]
 get_user_pages_unlocked+0x1cb/0x7d0 mm/gup.c:2681
 hva_to_pfn_slow virt/kvm/kvm_main.c:2903 [inline]
 hva_to_pfn+0x871/0xd60 virt/kvm/kvm_main.c:2999
page last free pid 10182 tgid 10179 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1402 [inline]
 __free_frozen_pages+0x747/0x1040 mm/page_alloc.c:2943
 __folio_put+0x3b4/0x5f0 mm/swap.c:112
 folio_put include/linux/mm.h:2090 [inline]
 put_page include/linux/mm.h:2159 [inline]
 kvm_release_page_clean virt/kvm/kvm_main.c:2813 [inline]
 kvm_release_page_clean+0x1dc/0x250 virt/kvm/kvm_main.c:2807
 hva_to_pfn_retry virt/kvm/pfncache.c:246 [inline]
 __kvm_gpc_refresh+0x195d/0x22c0 virt/kvm/pfncache.c:330
 __kvm_gpc_activate+0x2ab/0x490 virt/kvm/pfncache.c:424
 kvm_gpc_activate_hva+0x73/0xa0 virt/kvm/pfncache.c:444
 kvm_xen_hvm_set_attr+0x395/0x16a0 arch/x86/kvm/xen.c:798
 kvm_arch_vm_ioctl+0x2a0/0x18d0 arch/x86/kvm/x86.c:7528
 kvm_vm_ioctl+0x1564/0x4050 virt/kvm/kvm_main.c:5380
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804c76d800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804c76d880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804c76d900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                   ^
 ffff88804c76d980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804c76da00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
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