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SubjectKASAN: slab-out-of-bounds Read in kvm_read_guest_page
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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=16e40efbe00000
kernel config: https://syzkaller.appspot.com/x/.config?x=91b674b8f0368e69
dashboard link: https://syzkaller.appspot.com/bug?extid=a65b3f8eec6b27650a25
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14869db7e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10d2731fe00000

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=10a24a5de00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=12a24a5de00000
console output: https://syzkaller.appspot.com/x/log.txt?x=14a24a5de00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a65b3f8eec6b27650a25@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 gfn_to_memslot arch/x86/kvm/../../../virt/kvm/kvm_main.c:1597 [inline]
BUG: KASAN: slab-out-of-bounds in kvm_read_guest_page+0x4b5/0x4d0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2261
Read of size 8 at addr ffff8880953fd468 by task syz-executor431/6995

CPU: 1 PID: 6995 Comm: syz-executor431 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]
gfn_to_memslot arch/x86/kvm/../../../virt/kvm/kvm_main.c:1597 [inline]
kvm_read_guest_page+0x4b5/0x4d0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2261
kvm_read_guest+0x51/0xd0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2284
kvm_write_wall_clock arch/x86/kvm/x86.c:1721 [inline]
kvm_set_msr_common+0xdf3/0x27c0 arch/x86/kvm/x86.c:2851
vmx_set_msr+0xa83/0x26a0 arch/x86/kvm/vmx/vmx.c:2183
__kvm_set_msr+0x15f/0x2d0 arch/x86/kvm/x86.c:1504
__msr_io arch/x86/kvm/x86.c:3262 [inline]
msr_io+0x173/0x290 arch/x86/kvm/x86.c:3298
kvm_arch_vcpu_ioctl+0x1004/0x2c20 arch/x86/kvm/x86.c:4355
kvm_vcpu_ioctl+0x866/0xe60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3291
kvm_vcpu_compat_ioctl+0x1ab/0x350 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3334
__do_compat_sys_ioctl fs/ioctl.c:857 [inline]
__se_compat_sys_ioctl fs/ioctl.c:808 [inline]
__ia32_compat_sys_ioctl+0x23d/0x2b0 fs/ioctl.c:808
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x270/0xe90 arch/x86/entry/common.c:396
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Allocated by task 6995:
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
kvm_vm_compat_ioctl+0x125/0x240 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3798
__do_compat_sys_ioctl fs/ioctl.c:857 [inline]
__se_compat_sys_ioctl fs/ioctl.c:808 [inline]
__ia32_compat_sys_ioctl+0x23d/0x2b0 fs/ioctl.c:808
do_syscall_32_irqs_on arch/x86/entry/common.c:337 [inline]
do_fast_syscall_32+0x270/0xe90 arch/x86/entry/common.c:396
entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8880953fd000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1128 bytes inside of
2048-byte region [ffff8880953fd000, ffff8880953fd800)
The buggy address belongs to the page:
page:ffffea000254ff40 refcount:1 mapcount:0 mapping:00000000f2d13e61 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea000290dd48 ffffea00029c98c8 ffff8880aa000e00
raw: 0000000000000000 ffff8880953fd000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880953fd300: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8880953fd380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880953fd400: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
^
ffff8880953fd480: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880953fd500: 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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