On Fri, Jan 8, 2016 at 10:15 PM, Jeff Merkey <linux.mdb@xxxxxxxxx> wrote: > 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 + more kvm people -- 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
