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SubjectKASAN: slab-out-of-bounds Read in kvm_vcpu_gfn_to_memslot
From
Hello,

syzbot found the following crash on:

HEAD commit: bef7b2a7 Merge tag 'devicetree-for-5.7' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15ce12cde00000
kernel config: https://syzkaller.appspot.com/x/.config?x=91b674b8f0368e69
dashboard link: https://syzkaller.appspot.com/bug?extid=89a42836ac72e6a02d35
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14c69db7e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17b8b02be00000

The bug was bisected to:

commit 36947254e5f981aeeedab1c7dfa35fc34d330e80
Author: Sean Christopherson <sean.j.christopherson@intel.com>
Date: Tue Feb 18 21:07:32 2020 +0000

KVM: Dynamically size memslot array based on number of used slots

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=15f1b1fbe00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=17f1b1fbe00000
console output: https://syzkaller.appspot.com/x/log.txt?x=13f1b1fbe00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+89a42836ac72e6a02d35@syzkaller.appspotmail.com
Fixes: 36947254e5f9 ("KVM: Dynamically size memslot array based on number of used slots")

L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/l1tf.html for details.
==================================================================
BUG: KASAN: slab-out-of-bounds in search_memslots include/linux/kvm_host.h:1051 [inline]
BUG: KASAN: slab-out-of-bounds in __gfn_to_memslot include/linux/kvm_host.h:1063 [inline]
BUG: KASAN: slab-out-of-bounds in kvm_vcpu_gfn_to_memslot+0x50e/0x540 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1603
Read of size 8 at addr ffff88809e3bb468 by task syz-executor088/7241

CPU: 1 PID: 7241 Comm: syz-executor088 Not tainted 5.6.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x188/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd3/0x315 mm/kasan/report.c:374
__kasan_report.cold+0x35/0x4d mm/kasan/report.c:503
kasan_report+0x33/0x50 mm/kasan/common.c:648
search_memslots include/linux/kvm_host.h:1051 [inline]
__gfn_to_memslot include/linux/kvm_host.h:1063 [inline]
kvm_vcpu_gfn_to_memslot+0x50e/0x540 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1603
try_async_pf+0x12b/0xac0 arch/x86/kvm/mmu/mmu.c:4097
direct_page_fault+0x27d/0x1d70 arch/x86/kvm/mmu/mmu.c:4146
kvm_mmu_do_page_fault arch/x86/kvm/mmu.h:115 [inline]
kvm_mmu_page_fault+0x187/0x15d0 arch/x86/kvm/mmu/mmu.c:5446
vmx_handle_exit+0x2b8/0x1700 arch/x86/kvm/vmx/vmx.c:5953
vcpu_enter_guest+0xfea/0x59d0 arch/x86/kvm/x86.c:8470
vcpu_run arch/x86/kvm/x86.c:8533 [inline]
kvm_arch_vcpu_ioctl_run+0x3fb/0x16a0 arch/x86/kvm/x86.c:8755
kvm_vcpu_ioctl+0x493/0xe60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3138
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl+0x11a/0x180 fs/ioctl.c:763
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x440209
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffd115ca0d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440209
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000246 R12: 0000000000401a90
R13: 0000000000401b20 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 7241:
save_stack+0x1b/0x80 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:518 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:491
kmalloc_node include/linux/slab.h:578 [inline]
kvmalloc_node+0x61/0xf0 mm/util.c:574
kvmalloc include/linux/mm.h:733 [inline]
kvzalloc include/linux/mm.h:741 [inline]
kvm_dup_memslots arch/x86/kvm/../../../virt/kvm/kvm_main.c:1101 [inline]
kvm_set_memslot+0x115/0x1530 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1118
__kvm_set_memory_region+0xcf7/0x1320 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1300
kvm_set_memory_region+0x29/0x50 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1321
kvm_vm_ioctl_set_memory_region arch/x86/kvm/../../../virt/kvm/kvm_main.c:1333 [inline]
kvm_vm_ioctl+0x678/0x23e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3604
vfs_ioctl fs/ioctl.c:47 [inline]
ksys_ioctl+0x11a/0x180 fs/ioctl.c:763
__do_sys_ioctl fs/ioctl.c:772 [inline]
__se_sys_ioctl fs/ioctl.c:770 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:770
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff88809e3bb000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1128 bytes inside of
2048-byte region [ffff88809e3bb000, ffff88809e3bb800)
The buggy address belongs to the page:
page:ffffea000278eec0 refcount:1 mapcount:0 mapping:00000000c2601645 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00027b1b08 ffff8880aa001950 ffff8880aa000e00
raw: 0000000000000000 ffff88809e3bb000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809e3bb300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88809e3bb380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88809e3bb400: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
^
ffff88809e3bb480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809e3bb500: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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