Re: KMSAN: kernel-infoleak in __kvm_write_guest_page

[Dmitry Vyukov]

On Thu, Dec 6, 2018 at 10:01 AM syzbot
<syzbot+af22f34edec5361fb143@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> 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

#syz dup: KMSAN: kernel-infoleak in kvm_vcpu_write_guest_page

> ==================================================================
> 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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