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SubjectKASAN: slab-out-of-bounds Write in fpstate_init
From
Hello,

syzbot found the following crash on:

HEAD commit: 6648e120dd1a Add linux-next specific files for 20181217
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16fddf97400000
kernel config: https://syzkaller.appspot.com/x/.config?x=9e2825c86a37329f
dashboard link: https://syzkaller.appspot.com/bug?extid=5ce1a620488e94bf2f15
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=107348c3400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=135f5b1b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5ce1a620488e94bf2f15@syzkaller.appspotmail.com

audit: type=1800 audit(1545532930.544:30): pid=6029 uid=0 auid=4294967295
ses=4294967295 subj==unconfined op=collect_data cause=failed(directio)
comm="startpar" name="rmnologin" dev="sda1" ino=2423 res=0
sshd (6168) used greatest stack depth: 15728 bytes left
L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and
https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html for details.
==================================================================
BUG: KASAN: slab-out-of-bounds in memset include/linux/string.h:337 [inline]
BUG: KASAN: slab-out-of-bounds in fpstate_init+0x50/0x160
arch/x86/kernel/fpu/core.c:178
Write of size 832 at addr ffff8881bba4bbc0 by task syz-executor233/6184

CPU: 1 PID: 6184 Comm: syz-executor233 Not tainted
4.20.0-rc6-next-20181217+ #172
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+0x244/0x39d lib/dump_stack.c:113
print_address_description.cold.4+0x9/0x1ff mm/kasan/report.c:187
kasan_report.cold.5+0x1b/0x39 mm/kasan/report.c:317
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x13e/0x1b0 mm/kasan/generic.c:191
memset+0x23/0x40 mm/kasan/common.c:113
memset include/linux/string.h:337 [inline]
fpstate_init+0x50/0x160 arch/x86/kernel/fpu/core.c:178
fx_init arch/x86/kvm/x86.c:8646 [inline]
kvm_arch_vcpu_init+0x3e9/0x870 arch/x86/kvm/x86.c:9006
kvm_vcpu_init+0x2fa/0x420 arch/x86/kvm/../../../virt/kvm/kvm_main.c:315
vmx_create_vcpu+0x1b7/0x2695 arch/x86/kvm/vmx/vmx.c:6375
kvm_arch_vcpu_create+0xe5/0x220 arch/x86/kvm/x86.c:8679
kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:2555
[inline]
kvm_vm_ioctl+0x526/0x2030 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3084
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440039
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:00007ffe478aae78 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440039
RDX: 0000000000000000 RSI: 000000000000ae41 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000217 R12: 00000000004018c0
R13: 0000000000401950 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 6184:
save_stack+0x43/0xd0 mm/kasan/common.c:73
set_track mm/kasan/common.c:85 [inline]
kasan_kmalloc+0xcb/0xd0 mm/kasan/common.c:482
kasan_slab_alloc+0x12/0x20 mm/kasan/common.c:397
kmem_cache_alloc+0x130/0x730 mm/slab.c:3541
kmem_cache_zalloc include/linux/slab.h:730 [inline]
vmx_create_vcpu+0x110/0x2695 arch/x86/kvm/vmx/vmx.c:6366
kvm_arch_vcpu_create+0xe5/0x220 arch/x86/kvm/x86.c:8679
kvm_vm_ioctl_create_vcpu arch/x86/kvm/../../../virt/kvm/kvm_main.c:2555
[inline]
kvm_vm_ioctl+0x526/0x2030 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3084
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 0:
(stack is not available)

The buggy address belongs to the object at ffff8881bba4bb80
which belongs to the cache x86_fpu of size 832
The buggy address is located 64 bytes inside of
832-byte region [ffff8881bba4bb80, ffff8881bba4bec0)
The buggy address belongs to the page:
page:ffffea0006ee92c0 count:1 mapcount:0 mapping:ffff8881d7a9d380 index:0x0
flags: 0x2fffc0000000200(slab)
raw: 02fffc0000000200 ffff8881d6780448 ffff8881d6780448 ffff8881d7a9d380
raw: 0000000000000000 ffff8881bba4b040 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8881bba4bd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff8881bba4be00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffff8881bba4be80: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
^
ffff8881bba4bf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8881bba4bf80: 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.
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