On 1/8/16, Jeff Merkey <linux.mdb@xxxxxxxxx> wrote: > On 1/8/16, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: >> Hello, >> >> The following program triggers GPF in native_set_debugreg if run in >> a parallel loop: >> >> // autogenerated by syzkaller (http://github.com/google/syzkaller) >> #include <unistd.h> >> #include <sys/syscall.h> >> #include <string.h> >> #include <stdint.h> >> #include <pthread.h> >> >> long r[8]; >> >> void *thr(void *arg) >> { >> switch ((long)arg) { >> case 0: >> r[0] = syscall(SYS_mmap, 0x20000000ul, 0x7000ul, >> 0x3ul, 0x32ul, 0xfffffffffffffffful, 0x0ul); >> break; >> case 1: >> memcpy((void*)0x200008ab, >> "\x2f\x64\x65\x76\x2f\x6b\x76\x6d", 8); >> r[2] = syscall(SYS_open, 0x200008abul, 0x0ul, 0x0ul, 0, >> 0, >> 0); >> break; >> case 2: >> r[3] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, >> 0); >> break; >> case 3: >> r[4] = syscall(SYS_ioctl, r[3], 0xae41ul, 0x7ul, 0, 0, >> 0); >> break; >> case 4: >> r[5] = syscall(SYS_ioctl, r[4], 0xae80ul, 0, 0, 0, 0); >> break; >> case 5: >> memcpy((void*)0x20001000, >> "\x5d\x6a\x6b\xe8\x57\x3b\x4b\x7e\xcf\x0d\xa1\x72\xa3\x4a\x29\x0c\xfc\x6d\x44\x00\xa7\x52\xc7\xd8\x00\xdb\x89\x9d\x78\xb5\x54\x6b\x6b\x13\x1c\xe9\x5e\xd3\x0e\x40\x6f\xb4\x66\xf7\x5b\xe3\x36\xcb", >> 48); >> r[7] = syscall(SYS_ioctl, r[4], 0x4080aea2ul, >> 0x20001000ul, 0, 0, 0); >> break; >> } >> return 0; >> } >> >> int main() >> { >> long i; >> pthread_t th[6]; >> >> memset(r, -1, sizeof(r)); >> for (i = 0; i < 6; i++) { >> pthread_create(&th[i], 0, thr, (void*)i); >> usleep(10000); >> } >> for (i = 0; i < 6; i++) { >> pthread_create(&th[i], 0, thr, (void*)i); >> if (i%2==0) >> usleep(10000); >> } >> usleep(100000); >> return 0; >> } >> >> >> kasan: GPF could be caused by NULL-ptr deref or user memory >> accessgeneral protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN >> Modules linked in: >> CPU: 0 PID: 8491 Comm: syz-executor Not tainted 4.4.0-rc8+ #217 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs >> 01/01/2011 >> task: ffff8800631c8000 ti: ffff880065380000 task.ti: ffff880065380000 >> RIP: 0010:[<ffffffff8125fa5e>] [<ffffffff8125fa5e>] >> native_set_debugreg+0x2e/0x40 >> RSP: 0018:ffff880065387a88 EFLAGS: 00000097 >> RAX: ffff8800631c8000 RBX: ffff880063423478 RCX: ffff8800631c87c8 >> RDX: 0000000000000000 RSI: 400ed35ee91c136b RDI: 0000000000000006 >> RBP: ffff880065387a88 R08: 0000000000000001 R09: 0000000000000002 >> R10: 0000000000000001 R11: 0000000000000001 R12: 1ffffffff0e09f6d >> R13: ffff880063420030 R14: ffff880063420000 R15: ffff88006342002c >> FS: 00007f8ed68a7700(0000) GS:ffff88003ec00000(0000) >> knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b >> CR2: 0000000001710000 CR3: 000000006486d000 CR4: 00000000000026f0 >> DR0: 7e4b3b57e86b6a5d DR1: 0c294aa372a10dcf DR2: d8c752a700446dfc >> DR3: 6b54b5789d89db00 DR6: 00000000ffff0ff0 DR7: 0000000000000400 >> Stack: >> ffff880065387c10 ffffffff8106c3a6 ffffffff81067de4 ffff880065387b38 >> 0000000000000000 00000000002794c8 ffff880065380008 0000001b540f2184 >> 0000000000000000 1ffff1000ca70001 ffff880065380000 ffff880063421ac8 >> Call Trace: >> [< inline >] set_debugreg ./arch/x86/include/asm/paravirt.h:45 >> [< inline >] vcpu_enter_guest arch/x86/kvm/x86.c:6532 >> [< inline >] vcpu_run arch/x86/kvm/x86.c:6660 >> [<ffffffff8106c3a6>] kvm_arch_vcpu_ioctl_run+0x47b6/0x5820 >> arch/x86/kvm/x86.c:6818 >> [<ffffffff8101cf61>] kvm_vcpu_ioctl+0x5f1/0xd00 >> arch/x86/kvm/../../../virt/kvm/kvm_main.c:2375 >> [< inline >] vfs_ioctl fs/ioctl.c:43 >> [<ffffffff817b36b1>] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:607 >> [< inline >] SYSC_ioctl fs/ioctl.c:622 >> [<ffffffff817b3eff>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613 >> [<ffffffff85e745b6>] entry_SYSCALL_64_fastpath+0x16/0x7a >> arch/x86/entry/entry_64.S:185 >> Code: 07 48 89 e5 77 27 89 ff ff 24 fd c0 25 f3 85 0f 23 fe 5d c3 0f >> 23 c6 5d c3 0f 23 ce 5d c3 0f 23 d6 5d c3 0f 23 de 5d c3 0f 23 f6 <5d> >> c3 0f 0b 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 83 ff >> RIP [<ffffffff8125fa5e>] native_set_debugreg+0x2e/0x40 >> ./arch/x86/include/asm/debugreg.h:65 >> RSP <ffff880065387a88> >> ---[ end trace 94251fd7c32f126a ]--- >> >> >> On commit b06f3a168cdcd80026276898fd1fee443ef25743 (Jan 6). >> > > > The only place native_set_debugreg references memory is a jmpq > instruction (6th instruction into the function) that handles the C > switch statement then jumps to set the debugreg. RDI (edi) is set to > 6, so someone was setting debugreg 6 (probably with garbage status). > I guess this hardware GPF'd when someone tried to write to dr6. > > native_set_debugreg > push rbp > cmp 7,edi > mov rsp,rbp > ja +0x41 > move edi,edi > jmpq ptr @(rdi,8) > > then several mov rsi, db#(0-7) > > > Interesting it crashes when someone is writing to DR6. I have already > reported this issue. > > Jeff > thread-debugreg6 is pointing off to invalid memory. Jeff -- 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
