On Mon, Jun 29, 2020 at 05:29:56PM +0200, Andrey Konovalov wrote: > On Mon, Jun 29, 2020 at 5:25 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > > > > The reproducer has nothing to do with KVM: > > > > # https://syzkaller.appspot.com/bug?id=c356395d480ca736b00443ad89cd76fd7d209013 > > # See https://goo.gl/kgGztJ for information about syzkaller reproducers. > > #{"repeat":true,"procs":1,"sandbox":"","fault_call":-1,"close_fds":false,"segv":true} > > r0 = openat$fb0(0xffffffffffffff9c, &(0x7f0000000180)='/dev/fb0\x00', 0x0, 0x0) > > ioctl$FBIOPUT_VSCREENINFO(r0, 0x4601, &(0x7f0000000000)={0x0, 0x80, 0xc80, 0x0, 0x2, 0x1, 0x4, 0x0, {0x0, 0x0, 0x1}, {0x0, 0x0, 0xfffffffc}, {}, {}, 0x0, 0x40}) > > > > but the stack trace does. On the other hand, the address seems okay: > > > > kvm_cpu_caps+0x24/0x50 > > > > and there are tons of other kvm_cpu_cap_get calls that aren't causing > > KASAN to complain. The variable is initialized from > > > > kvm_arch_hardware_setup > > hardware_setup (in arch/x86/kvm/vmx/vmx.c) > > vmx_set_cpu_caps > > kvm_set_cpu_caps > > > > with a simple memcpy that writes the entire array. Does anyone understand > > what is going on here? > > Most likely a bug in /dev/fb handlers caused a memory corruption in > kvm related memory. That's my assumption as well. There's another syzbot failure[*] that points at KVM but whose reproducer is a single FBIOPUT_VSCREENINFO. In that case, the pointer from "&cpu_data(smp_processor_id())" is NULL, i.e. highly unlikely to be a KVM bug. [*] https://lkml.kernel.org/r/000000000000077a6505a8bf57b2@xxxxxxxxxx > > Paolo > > > > On 27/06/20 22:01, syzbot wrote: > > > BUG: KASAN: out-of-bounds in kvm_cpu_cap_get arch/x86/kvm/cpuid.h:292 [inline] > > > BUG: KASAN: out-of-bounds in kvm_cpu_cap_has arch/x86/kvm/cpuid.h:297 [inline] > > > BUG: KASAN: out-of-bounds in kvm_init_msr_list arch/x86/kvm/x86.c:5362 [inline] > > > BUG: KASAN: out-of-bounds in kvm_arch_hardware_setup+0xb05/0xf40 arch/x86/kvm/x86.c:9802 > > > Read of size 4 at addr ffffffff896c3134 by task syz-executor614/6786 > > > > > > CPU: 1 PID: 6786 Comm: syz-executor614 Not tainted 5.7.0-syzkaller #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > > > Call Trace: > > > <IRQ> > > > __dump_stack lib/dump_stack.c:77 [inline] > > > dump_stack+0x1e9/0x30e lib/dump_stack.c:118 > > > print_address_description+0x66/0x5a0 mm/kasan/report.c:383 > > > __kasan_report mm/kasan/report.c:513 [inline] > > > kasan_report+0x132/0x1d0 mm/kasan/report.c:530 > > > kvm_cpu_cap_get arch/x86/kvm/cpuid.h:292 [inline] > > > kvm_cpu_cap_has arch/x86/kvm/cpuid.h:297 [inline] > > > kvm_init_msr_list arch/x86/kvm/x86.c:5362 [inline] > > > kvm_arch_hardware_setup+0xb05/0xf40 arch/x86/kvm/x86.c:9802 > > > </IRQ> > > > > > > The buggy address belongs to the variable: > > > kvm_cpu_caps+0x24/0x50 > > > > > > Memory state around the buggy address: > > > ffffffff896c3000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > > ffffffff896c3080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > >> ffffffff896c3100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > > ^ > > > ffffffff896c3180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > > ffffffff896c3200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > > > ================================================================== > > > > -- > > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@xxxxxxxxxxxxxxxx. > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/04786ba2-4934-c544-63d1-4d5d36dc5822%40redhat.com.
