It looks like userspace can possibly induce this by providing guest CPUID information with a "physical address width" of 64 in leaf 0x80000008. Perhaps cpuid_query_maxphyaddr() should just look at the low 5 bits of CPUID.80000008H:EAX? Better would be to return an error for out-of-range values, but I understand that the kvm community's stance is that, in general, guest CPUID information should not be validated by kvm. On Tue, Dec 22, 2020 at 12:36 AM syzbot <syzbot+e87846c48bf72bc85311@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hello, > > syzbot found the following issue on: > > HEAD commit: 5e60366d Merge tag 'fallthrough-fixes-clang-5.11-rc1' of g.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=11c7046b500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=db720fe37a6a41d8 > dashboard link: https://syzkaller.appspot.com/bug?extid=e87846c48bf72bc85311 > compiler: gcc (GCC) 10.1.0-syz 20200507 > userspace arch: i386 > > Unfortunately, I don't have any reproducer for this issue yet. > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+e87846c48bf72bc85311@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================================ > UBSAN: shift-out-of-bounds in arch/x86/kvm/mmu.h:52:16 > shift exponent 64 is too large for 64-bit type 'long long unsigned int' > CPU: 1 PID: 11156 Comm: syz-executor.1 Not tainted 5.10.0-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:79 [inline] > dump_stack+0x107/0x163 lib/dump_stack.c:120 > ubsan_epilogue+0xb/0x5a lib/ubsan.c:148 > __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:395 > rsvd_bits arch/x86/kvm/mmu.h:52 [inline] > kvm_vcpu_after_set_cpuid.cold+0x35/0x3a arch/x86/kvm/cpuid.c:181 > kvm_vcpu_ioctl_set_cpuid+0x28e/0x970 arch/x86/kvm/cpuid.c:273 > kvm_arch_vcpu_ioctl+0x1091/0x2d70 arch/x86/kvm/x86.c:4699 > kvm_vcpu_ioctl+0x7b9/0xdb0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3386 > kvm_vcpu_compat_ioctl+0x1a2/0x340 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3430 > __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842 > do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline] > __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:137 > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160 > entry_SYSENTER_compat_after_hwframe+0x4d/0x5c > RIP: 0023:0xf7fe8549 > Code: b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 00 00 00 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90 > RSP: 002b:00000000f55e20cc EFLAGS: 00000296 ORIG_RAX: 0000000000000036 > RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 000000004008ae8a > RDX: 00000000200000c0 RSI: 0000000000000000 RDI: 0000000000000000 > RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > ================================================================================ > > > --- > This report 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@xxxxxxxxxxxxxxxx. > > syzbot will keep track of this issue. See: > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
