On Fri, Dec 15, 2017 at 10:07 AM, Dmitry Vyukov <dvyu...@google.com> wrote: > On Thu, Dec 14, 2017 at 10:39 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: >> On Thu, Dec 14, 2017 at 1:27 PM, Andy Lutomirski <l...@kernel.org> wrote: >>> On Thu, Dec 14, 2017 at 11:28 AM, Linus Torvalds >>> <torva...@linux-foundation.org> wrote: >>>> I don't think that's the case. "int3" is entirely synchronous, and >>>> doesn't have the same odd issues as a breakpoint trap (which honors RF >>>> etc). It's literally just a one-byte shorthand for "int $3". >>> >>> The SDM says precisely the same thing about INT N, so, whichever way >>> you dice it, int3 is a benign exception. >> >> That just means that it doesn't double-fault when it takes the page fault. >> >> Which we already know, because we see a page fault, not a double fault. >> >>> 0xfffffffffffffff8 is *exactly* where the fault would be if the >>> microcoded push of SS faulted if the IST contained zeros. >> >> Yes, I suspect it's the stack that is buggered for some reason. >> >>>> Plus I think the instruction that gets overwritten is just a 5-byte >>>> nop isn't it? So it really shouldn't take a fault without the "int3" >>>> overwriting. >>> >>> Unless it was being overwritten the other way and the oops hit while >>> tracing was being turned *off*. >> >> Doesn't really matter. The two forms of that instruction are "5-byte >> nop" and "unconditional branch". >> >> Neither of them will write to anything - the only page fault they >> could take is for instruction fetch. >> >> So it really must be the "int3" that fails. Unless we're looking at >> some odd CPU errata, which sounds very very unlikely. > > FTR the commit is: > > commit d127129e85a020879f334154300ddd3f7ec21c1e (HEAD, tag: next-20171129) > Author: Stephen Rothwell <s...@canb.auug.org.au> > Date: Wed Nov 29 14:09:56 2017 +1100 > Add linux-next specific files for 20171129 > > You can get it from > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next-history.git > Compiler is this: https://storage.googleapis.com/syzkaller/gcc-7.tar.gz > Config was attached. > > I've built this exact kernel and here is __switch_to disasm: > https://gist.githubusercontent.com/dvyukov/8137559f7da08fbe32f9018972a4498c/raw/0ef2abf723b117f0d0f0306fd50e216d50c5cecb/gistfile1.txt > > __switch_to+0x95b seems to point to (?): > > ffffffff81252f6b: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1) > > which is branch target alignment nop. > > We have a bunch of semi-similar non-sense crashes on syzbot: > > https://groups.google.com/forum/#!msg/syzkaller-bugs/zGz7AVtMBV0/X_-CPbjNAgAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/9nMSJo9jmGs/tkRYgZ-XAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/04-q4OZrerA/XfYdNnWXAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/6iC6rPtAHKQ/UiZ4fnWXAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/2zSDbzRIH_k/SLCMqmeXAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/uEsjx8VISco/Mwu_pbGWAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/kZ6Z7UQLbCQ/JHpjTGeXAwAJ > https://groups.google.com/forum/#!msg/syzkaller-bugs/UjYsJxiGxwU/mponQq2XAwAJ > > Lots of them are on 0xfffffffffffffff8 address. > > I have some suspicion towards KVM. Potentially a nested KVM messed > host processor state (CRn or page tables) so that then we get these > weird crashes. > > One question: how would triple-fault look like? I am asking because we > have hundreds of cases where kernel just starts silently rebooting > while running some unprivileged syscalls: > https://groups.google.com/forum/#!msg/syzkaller-bugs/w8dkVNrgzrc/4mLJLOAbCgAJ > Can these be triple faults? Reproducer for that one also seems to be > related to KVM.
Well, actually replying log for this crash and for https://groups.google.com/forum/#!msg/syzkaller-bugs/zGz7AVtMBV0/X_-CPbjNAgAJ with: ./syz-execprog -procs=10 -sandbox=namespace -repeat=0 raw.txt (you can find exact instructions on how to do this here https://github.com/google/syzkaller/blob/master/docs/executing_syzkaller_programs.md) I've got: [ 121.553588] binder: 3856:3857 ioctl 40046205 0 returned -22 [ 121.557656] binder: 3856:3857 ERROR: BC_REGISTER_LOOPER called without request [ 121.559744] binder: 3857 RLIMIT_NICE not set [ 121.586339] binder: 3857 RLIMIT_NICE not set [ 121.591764] binder: 3856:3857 unknown command 1400526783 [ 121.593226] binder: 3856:3857 ioctl c0306201 20002fd0 returned -22 [ 121.598292] binder: 3857 RLIMIT_NICE not set [ 121.600827] binder: 3856:3857 ioctl c018620b 20000fe8 returned -14 [ 121.618284] binder: 3856:3857 BC_FREE_BUFFER uffffffffffffffff no match [ 121.622181] binder: 3856:3857 got reply transaction with no transaction stack [ 121.626345] binder: 3856:3857 transaction failed 29201/-71, size 72-56 line 2747 [ 121.628912] binder: 3856:3857 ioctl c0306201 20005fd0 returned -14 [ 121.635620] binder: unexpected work type, 4, not freed [ 121.639753] binder: undelivered TRANSACTION_COMPLETE [ 121.645213] binder: undelivered TRANSACTION_ERROR: 29201 [ 121.654860] binder: 3856:3857 BC_FREE_BUFFER u00000000ffffffff no match [ 121.667216] *** Guest State *** [ 121.667728] CR0: actual=0x0000000000000030, shadow=0x0000000060000010, gh_mask=fffffffffffffff7 early console in extract_kernel input_data: 0x0000000005f13276 input_len: 0x0000000001e7fa4c output: 0x0000000001000000 output_len: 0x0000000005c85958 kernel_total_size: 0x0000000006db2000 Decompressing Linux... Parsing ELF... done. Booting the kernel. [ 0.000000] Linux version 4.15.0-rc1-next-20171129 (dvyu...@dvyukov-z840.muc.corp.google.com) (gcc version 7.1.1 20170620 (GCC)) #1 SMP Fri Dec 15 09:25:01 CET 2017 [ 0.000000] Command line: kvm-intel.nested=1 kvm-intel.unrestricted_guest=1 kvm-intel.ept=1 kvm-intel.flexpriority=1 kvm-intel.vpid=1 kvm-intel.emulate_invalid_guest_state=1 kvm-intel.eptad=1 kvm-intel.enable_shadow_vmcs=1 kvm-intel.pml=1 kvm-intel.enable_apicv=1 console=ttyS0 root=/dev/sda earlyprintk=serial slub_debug=UZ vsyscall=native rodata=n oops=panic panic_on_warn=1 panic=86400 [ 0.000000] x86/fpu: Supporting XSAVE feature 0x001: 'x87 floating point registers' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x002: 'SSE registers' [ 0.000000] x86/fpu: Supporting XSAVE feature 0x004: 'AVX registers' [ 0.000000] x86/fpu: xstate_offset[2]: 576, xstate_sizes[2]: 256 [ 0.000000] x86/fpu: Enabled xstate features 0x7, context size is 832 bytes, using 'standard' format. [ 0.000000] e820: BIOS-provided physical RAM map: ...
