On Fri, Jan 13, 2017 at 6:47 PM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > 2017-01-12 14:55+0100, Dmitry Vyukov: >> Hello, >> >> I've got the following WARNING in x86_emulate_insn while running >> syzkaller fuzzer: >> >> WARNING: CPU: 2 PID: 18646 at arch/x86/kvm/emulate.c:5558 >> x86_emulate_insn+0x16a5/0x4090 arch/x86/kvm/emulate.c:5572 >> Modules linked in: >> CPU: 2 PID: 18646 Comm: syz-executor Not tainted 4.10.0-rc3+ #155 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> Call Trace: >> __dump_stack lib/dump_stack.c:15 [inline] >> dump_stack+0x292/0x3a2 lib/dump_stack.c:51 >> __warn+0x19f/0x1e0 kernel/panic.c:547 >> warn_slowpath_null+0x2c/0x40 kernel/panic.c:582 >> x86_emulate_insn+0x16a5/0x4090 arch/x86/kvm/emulate.c:5572 >> x86_emulate_instruction+0x403/0x1cc0 arch/x86/kvm/x86.c:5618 >> emulate_instruction arch/x86/include/asm/kvm_host.h:1127 [inline] >> handle_exception+0x594/0xfd0 arch/x86/kvm/vmx.c:5762 >> vmx_handle_exit+0x2b7/0x38b0 arch/x86/kvm/vmx.c:8625 >> vcpu_enter_guest arch/x86/kvm/x86.c:6888 [inline] >> vcpu_run arch/x86/kvm/x86.c:6947 [inline] >> kvm_arch_vcpu_ioctl_run+0xf3d/0x4660 arch/x86/kvm/x86.c:7105 >> kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2569 >> vfs_ioctl fs/ioctl.c:43 [inline] >> do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:683 >> SYSC_ioctl fs/ioctl.c:698 [inline] >> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689 >> entry_SYSCALL_64_fastpath+0x1f/0xc2 >> RIP: 0033:0x445329 >> RSP: 002b:00007f9e6e22fb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010 >> RAX: ffffffffffffffda RBX: 0000000000000018 RCX: 0000000000445329 >> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000018 >> RBP: 00000000006deb40 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000700150 >> R13: 0000000000000000 R14: 00007f9e6e2309c0 R15: 00007f9e6e230700 >> ---[ end trace 6b54f749506b620c ]--- >> ------------[ cut here ]------------ >> WARNING: CPU: 2 PID: 18646 at arch/x86/kvm/x86.c:366 >> exception_type+0x73/0x80 arch/x86/kvm/x86.c:366 >> Modules linked in: >> CPU: 2 PID: 18646 Comm: syz-executor Tainted: G W 4.10.0-rc3+ #155 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> Call Trace: >> __dump_stack lib/dump_stack.c:15 [inline] >> dump_stack+0x292/0x3a2 lib/dump_stack.c:51 >> __warn+0x19f/0x1e0 kernel/panic.c:547 >> warn_slowpath_null+0x2c/0x40 kernel/panic.c:582 >> exception_type+0x73/0x80 arch/x86/kvm/x86.c:366 >> x86_emulate_instruction+0x1356/0x1cc0 arch/x86/kvm/x86.c:5664 >> emulate_instruction arch/x86/include/asm/kvm_host.h:1127 [inline] >> handle_exception+0x594/0xfd0 arch/x86/kvm/vmx.c:5762 >> vmx_handle_exit+0x2b7/0x38b0 arch/x86/kvm/vmx.c:8625 >> vcpu_enter_guest arch/x86/kvm/x86.c:6888 [inline] >> vcpu_run arch/x86/kvm/x86.c:6947 [inline] >> kvm_arch_vcpu_ioctl_run+0xf3d/0x4660 arch/x86/kvm/x86.c:7105 >> kvm_vcpu_ioctl+0x673/0x1120 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2569 >> vfs_ioctl fs/ioctl.c:43 [inline] >> do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:683 >> SYSC_ioctl fs/ioctl.c:698 [inline] >> SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689 >> entry_SYSCALL_64_fastpath+0x1f/0xc2 >> RIP: 0033:0x445329 >> RSP: 002b:00007f9e6e22fb58 EFLAGS: 00000286 ORIG_RAX: 0000000000000010 >> RAX: ffffffffffffffda RBX: 0000000000000018 RCX: 0000000000445329 >> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000018 >> RBP: 00000000006deb40 R08: 0000000000000000 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000700150 >> R13: 0000000000000000 R14: 00007f9e6e2309c0 R15: 00007f9e6e230700 >> ---[ end trace 6b54f749506b620d ]--- >> >> On commit ba836a6f5ab1243ff5e08a941a2d1de8b31244e1. >> >> Unfortunately I can't reproduce it with a C program. >> It reproduces with the following syzkaller program within a minute, though: >> https://gist.githubusercontent.com/dvyukov/d09118fb9d986a9385487d80a1b50680/raw/884c68d22c3a80778ae596a6c5daf7467ea41b68/gistfile1.txt >> It can be executed following these instructions: >> https://github.com/google/syzkaller/wiki/How-to-execute-syzkaller-programs >> I run syz-execprog as: >> ./syz-execprog -repeat=0 -procs=8 -sandbox=none gistfile1.txt >> >> Note that syz_kvm_setup_cpu is a pseudo syscall that setups vcpu into >> a complex state: >> https://github.com/google/syzkaller/blob/master/executor/common_kvm_amd64.h#L271 >> >> My bet would be on some race where VM memory is overwritten >> concurrently, and it affects either guest execution or >> emulate_instruction in a bad way... > > Yeah, all functions that return X86EMUL_PROPAGATE_FAULT seem to set > exception.vector to something sane. The only easy way to get a bad value there > is when x86_emulate_instruction() clears it to -1U, but I don't see how a race > would play out. > > Anyway, I can't reproduce on bare metal [got another warning, see below]. > Will try after rebuilding a guest kernel. I've dumped exception before the warning and they all look the same: [ 211.608578] vector=255 error_code_valid=0 error_code=0 nested_page_fault=0 address= (null) [ 211.609793] ------------[ cut here ]------------ [ 211.612438] WARNING: CPU: 3 PID: 1876 at arch/x86/kvm/emulate.c:5611 x86_emulate_insn+0x17bf/0x4240 Looks like no parts of it were written after initialization. I've also added just in case: static int emulate_exception(struct x86_emulate_ctxt *ctxt, int vec, u32 error, bool valid) { - WARN_ON(vec > 0x1f); + WARN_ON(vec > 0x1f || vec < 0); And it did _not_ fire. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
