Re: [syzbot] [kvm-x86?] KASAN: use-after-free Read in kvm_setup_guest_pvclock

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    7de6ae9e1220 Add linux-next specific files for 20260629
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=163d19de580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=93f99737ecde604c
dashboard link: https://syzkaller.appspot.com/bug?extid=fb7c2dd166d3ea63df2a
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1309af41580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11f28bae580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a09187a6eb8d/disk-7de6ae9e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f0a76dd86b32/vmlinux-7de6ae9e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/864b9d8296e7/bzImage-7de6ae9e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fb7c2dd166d3ea63df2a@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: use-after-free in kvm_setup_guest_pvclock+0x439/0x620 arch/x86/kvm/x86.c:1728
Read of size 4 at addr ffff88804d02c320 by task syz.1.180/6591

CPU: 1 UID: 0 PID: 6591 Comm: syz.1.180 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 kvm_setup_guest_pvclock+0x439/0x620 arch/x86/kvm/x86.c:1728
 kvm_guest_time_update+0xa32/0xe60 arch/x86/kvm/x86.c:1864
 vcpu_enter_guest arch/x86/kvm/x86.c:8038 [inline]
 vcpu_run+0x150d/0x73e0 arch/x86/kvm/x86.c:8596
 kvm_arch_vcpu_ioctl_run+0xe51/0x1960 arch/x86/kvm/x86.c:8929
 kvm_vcpu_ioctl+0xa64/0xfe0 virt/kvm/kvm_main.c:4470
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbebb04ce59
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:00007fbeba68d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fbebb2c6090 RCX: 00007fbebb04ce59
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
RBP: 00007fbebb0e2e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fbebb2c6128 R14: 00007fbebb2c6090 R15: 00007ffefb5754e8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x200000000 pfn:0x4d02c
flags: 0x80000000000000(node=0|zone=1)
raw: 0080000000000000 ffffea000159c008 ffff8880b8642f70 0000000000000000
raw: 0000000200000000 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 0x140dca(GFP_HIGHUSER_MOVABLE|__GFP_ZERO|__GFP_COMP), pid 6589, tgid 6589 (syz.1.180), ts 149074813359
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1861
 prep_new_page mm/page_alloc.c:1869 [inline]
 get_page_from_freelist+0x264c/0x26c0 mm/page_alloc.c:3949
 __alloc_frozen_pages_noprof+0x1a6/0x390 mm/page_alloc.c:5322
 alloc_pages_mpol+0xce/0x280 mm/mempolicy.c:2490
 folio_alloc_mpol_noprof+0x3b/0x1e0 mm/mempolicy.c:2509
 vma_alloc_folio_noprof+0xe1/0x1e0 mm/mempolicy.c:2544
 folio_prealloc mm/memory.c:-1 [inline]
 alloc_anon_folio mm/memory.c:5247 [inline]
 do_anonymous_page mm/memory.c:5342 [inline]
 do_pte_missing+0x835/0x28f0 mm/memory.c:4564
 handle_pte_fault mm/memory.c:6379 [inline]
 __handle_mm_fault mm/memory.c:6517 [inline]
 handle_mm_fault+0xe0b/0x1520 mm/memory.c:6686
 do_user_addr_fault+0xa4d/0x1340 arch/x86/mm/fault.c:1343
 handle_page_fault arch/x86/mm/fault.c:1483 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1536
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:595
page last free pid 6590 tgid 6589 ts 149102566230 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1408 [inline]
 __free_frozen_pages+0x10de/0x11c0 mm/page_alloc.c:2952
 __folio_put+0x30f/0x3c0 mm/swap.c:112
 hva_to_pfn_retry virt/kvm/pfncache.c:246 [inline]
 __kvm_gpc_refresh+0x1277/0x1710 virt/kvm/pfncache.c:330
 __kvm_gpc_activate+0x289/0x3b0 virt/kvm/pfncache.c:424
 kvm_xen_vcpu_set_attr+0x1d3/0x1190 arch/x86/kvm/xen.c:938
 kvm_arch_vcpu_ioctl+0x1467/0x23f0 arch/x86/kvm/x86.c:3815
 kvm_vcpu_ioctl+0x7e6/0xfe0 virt/kvm/kvm_main.c:4647
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88804d02c200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804d02c280: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff88804d02c300: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                               ^
 ffff88804d02c380: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff88804d02c400: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


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