> On 7 Nov 2018, at 20:58, syzbot <syzbot+a8ef68d71211ba264f56@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hello, > > syzbot found the following crash on: > > HEAD commit: 7438a3b20295 kmsan: print user address when reporting info.. > git tree: https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_google_kmsan.git_master&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=fcwxYfHP71V16E_WRx7hgde6KeNMFBzprI2k6PzzZEo&e= > console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D10d782f5400000&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=G8EVFBcgaTj-Rg8XsqlSgOVE7Hjg9gU5JEG7hA0ry1I&e= > kernel config: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D8df5fc509a1b351b&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=yxSBwzSyc6oRH7v1EJAKQMbq9VghK3Nme98FwYd8iJA&e= > dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3Da8ef68d71211ba264f56&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=FqvBbzpE2srFcjavB0i99ekCvznCaHFOuWgIwYzmrXs&e= > compiler: clang version 8.0.0 (trunk 343298) > syz repro: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D15f09133400000&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=0JDFhFc1yLDbhcyTkAE1NO9PulBlKC3ZAsRaieLSDWg&e= > C reproducer: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.c-3Fx-3D15a39e05400000&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=FSZ1iQgxwIrifJ7X_cwC7-L4zPR3qH5jVMEFYpP2770&e= > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+a8ef68d71211ba264f56@xxxxxxxxxxxxxxxxxxxxxxxxx > > L1TF CPU bug present and SMT on, data leak possible. See CVE-2018-3646 and https://urldefense.proofpoint.com/v2/url?u=https-3A__www.kernel.org_doc_html_latest_admin-2Dguide_l1tf.html&d=DwIBaQ&c=RoP1YumCXCgaWHvlZYR8PZh8Bv7qIrMUB65eapI_JnE&r=Jk6Q8nNzkQ6LJ6g42qARkg6ryIDGQr-yKXPNGZbpTx0&m=_zu2xJguqdkES0k8nx8UlglUdOiAHk72aWKl44bi2Sw&s=RlJUg93Uo3_bn1O3eehqy8r8h6IXBRoE0YNsIVFQY2A&e= for details. > ================================================================== > BUG: KMSAN: kernel-infoleak in __copy_to_user include/linux/uaccess.h:121 [inline] > BUG: KMSAN: kernel-infoleak in __kvm_write_guest_page arch/x86/kvm/../../../virt/kvm/kvm_main.c:1849 [inline] > BUG: KMSAN: kernel-infoleak in kvm_write_guest_page+0x373/0x500 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1861 > CPU: 1 PID: 6274 Comm: syz-executor149 Not tainted 4.19.0+ #78 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x32d/0x480 lib/dump_stack.c:113 > kmsan_report+0x19f/0x300 mm/kmsan/kmsan.c:911 > kmsan_internal_check_memory+0x35f/0x450 mm/kmsan/kmsan.c:993 > kmsan_copy_to_user+0x7c/0xe0 mm/kmsan/kmsan_hooks.c:552 > __copy_to_user include/linux/uaccess.h:121 [inline] > __kvm_write_guest_page arch/x86/kvm/../../../virt/kvm/kvm_main.c:1849 [inline] > kvm_write_guest_page+0x373/0x500 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1861 > kvm_write_guest+0x1e1/0x360 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1883 > kvm_pv_clock_pairing arch/x86/kvm/x86.c:6793 [inline] > kvm_emulate_hypercall+0x1c96/0x21b0 arch/x86/kvm/x86.c:6866 > handle_vmcall+0x41/0x50 arch/x86/kvm/vmx.c:7487 > vmx_handle_exit+0x1e81/0xbac0 arch/x86/kvm/vmx.c:10128 > vcpu_enter_guest arch/x86/kvm/x86.c:7667 [inline] > vcpu_run arch/x86/kvm/x86.c:7730 [inline] > kvm_arch_vcpu_ioctl_run+0xac32/0x11d80 arch/x86/kvm/x86.c:7930 > kvm_vcpu_ioctl+0xfb1/0x1f90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2590 > do_vfs_ioctl+0xf77/0x2d30 fs/ioctl.c:46 > ksys_ioctl fs/ioctl.c:702 [inline] > __do_sys_ioctl fs/ioctl.c:709 [inline] > __se_sys_ioctl+0x1da/0x270 fs/ioctl.c:707 > __x64_sys_ioctl+0x4a/0x70 fs/ioctl.c:707 > do_syscall_64+0xcf/0x110 arch/x86/entry/common.c:291 > entry_SYSCALL_64_after_hwframe+0x63/0xe7 > RIP: 0033:0x442b39 > Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 1b 0c fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007ffcb4e05478 EFLAGS: 00000217 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000442b39 > RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000007 > RBP: 00000000006cd018 R08: 0000000020000100 R09: 0000000020000100 > R10: 0000000000000000 R11: 0000000000000217 R12: 0000000000403be0 > R13: 0000000000403c70 R14: 0000000000000000 R15: 0000000000000000 > > Local variable description: ----clock_pairing.i@kvm_emulate_hypercall > Variable was created at: > kvm_emulate_hypercall+0x60/0x21b0 arch/x86/kvm/x86.c:6827 > handle_vmcall+0x41/0x50 arch/x86/kvm/vmx.c:7487 > > Bytes 28-63 of 64 are uninitialized > Memory access of size 64 starts at ffff8801aac5f3d8 > Data copied to user address 0000000020000000 > ================================================================== The info-leak here seems to be pretty obvious. kvm_pv_clock_pairing() copies entire “clock_pairing” var to guest using kvm_write_guest(), but it doesn’t initialize clock_pairing.pad[] bytes (which is exactly bytes 28-63). I will submit a patch to fix this… -Liran
