KMSAN: kernel-infoleak in __kvm_write_guest_page

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6f0597832d81 kmsan: unpoison data passed to skb_put_xxx() ..
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=10b6da5d400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9b071100dcf8e641
dashboard link: https://syzkaller.appspot.com/bug?extid=af22f34edec5361fb143
compiler:       clang version 8.0.0 (trunk 348261)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+af22f34edec5361fb143@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KMSAN: kernel-infoleak in __copy_to_user include/linux/uaccess.h:121  
[inline]
BUG: KMSAN: kernel-infoleak in __kvm_write_guest_page+0x2cc/0x4a0  
arch/x86/kvm/../../../virt/kvm/kvm_main.c:1855
CPU: 1 PID: 17704 Comm: syz-executor1 Not tainted 4.20.0-rc5+ #107
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+0x32d/0x480 lib/dump_stack.c:113
 kmsan_report+0x12d/0x290 mm/kmsan/kmsan.c:683
 kmsan_internal_check_memory+0x9ce/0xa50 mm/kmsan/kmsan.c:769
 kmsan_copy_to_user+0x8d/0xa0 mm/kmsan/kmsan_hooks.c:634
 __copy_to_user include/linux/uaccess.h:121 [inline]
 __kvm_write_guest_page+0x2cc/0x4a0  
arch/x86/kvm/../../../virt/kvm/kvm_main.c:1855
 kvm_vcpu_write_guest_page+0x196/0x1e0  
arch/x86/kvm/../../../virt/kvm/kvm_main.c:1876
 nested_release_vmcs12 arch/x86/kvm/vmx.c:8489 [inline]
 handle_vmptrld+0x1613/0x1750 arch/x86/kvm/vmx.c:9328
 vmx_handle_exit+0x213b/0xb920 arch/x86/kvm/vmx.c:10632
 vcpu_enter_guest arch/x86/kvm/x86.c:7811 [inline]
 vcpu_run arch/x86/kvm/x86.c:7874 [inline]
 kvm_arch_vcpu_ioctl_run+0xa551/0x11150 arch/x86/kvm/x86.c:8074
 kvm_vcpu_ioctl+0x1098/0x1e30 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2596
 do_vfs_ioctl+0xf36/0x2d30 fs/ioctl.c:46
 ksys_ioctl fs/ioctl.c:713 [inline]
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl+0x1da/0x270 fs/ioctl.c:718
 __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:718
 do_syscall_64+0xcd/0x110 arch/x86/entry/common.c:291
 entry_SYSCALL_64_after_hwframe+0x63/0xe7
RIP: 0033:0x457569
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0d0d3f0c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000006
RBP: 000000000072c040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f0d0d3f16d4
R13: 00000000004c034e R14: 00000000004d0bc0 R15: 00000000ffffffff

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:246 [inline]
 kmsan_internal_poison_shadow+0x92/0x150 mm/kmsan/kmsan.c:169
 kmsan_kmalloc+0xa1/0x100 mm/kmsan/kmsan_hooks.c:186
 kmem_cache_alloc_trace+0x6b7/0xe20 mm/slub.c:2789
 kmalloc include/linux/slab.h:546 [inline]
 enter_vmx_operation+0x105/0xe10 arch/x86/kvm/vmx.c:8315
 vmx_set_nested_state+0xdc9/0x18a0 arch/x86/kvm/vmx.c:14922
 kvm_arch_vcpu_ioctl+0x4d99/0x7370 arch/x86/kvm/x86.c:4190
 kvm_vcpu_ioctl+0xcf3/0x1e30 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2748
 do_vfs_ioctl+0xf36/0x2d30 fs/ioctl.c:46
 ksys_ioctl fs/ioctl.c:713 [inline]
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl+0x1da/0x270 fs/ioctl.c:718
 __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:718
 do_syscall_64+0xcd/0x110 arch/x86/entry/common.c:291
 entry_SYSCALL_64_after_hwframe+0x63/0xe7

Bytes 1000-4095 of 4096 are uninitialized
Memory access of size 4096 starts at ffff8881147db000
Data copied to user address 0000000020feb000
==================================================================


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