On 07/11/2017 06:06 PM, Andy Lutomirski wrote: > On Tue, Jul 11, 2017 at 3:35 AM, Kirill A. Shutemov > <kirill@xxxxxxxxxxxxx> wrote: >> On Mon, Jul 10, 2017 at 05:30:38PM -0700, Andy Lutomirski wrote: >>> On Mon, Jul 10, 2017 at 2:24 PM, Kirill A. Shutemov >>> <kirill@xxxxxxxxxxxxx> wrote: >>>> On Mon, Jul 10, 2017 at 01:07:13PM -0700, Andy Lutomirski wrote: >>>>> Can you give the disassembly of the backtrace lines? Blaming the >>>>> .endr doesn't make much sense to me. >>>> >>>> I don't have backtrace. It's before printk() is functional. I only see >>>> triple fault and reboot. >>>> >>>> I had to rely on qemu tracing and gdb. >>> >>> Can you ask GDB or objtool to disassemble around those addresses? Can >>> you also attach the big dump that QEMU throws out that shows register >>> state? In particular, CR2, CR3, and CR4 could be useful. >> >> The last three execptions: >> >> check_exception old: 0xffffffff new 0xe, cr2: 0xffffffff7ffffff8, rip: 0xffffffff84bb3036 >> RAX=00000000ffffffff RBX=ffffffff800000d8 RCX=ffffffff84be4021 RDX=dffffc0000000000 >> RSI=0000000000000006 RDI=ffffffff84c57000 RBP=ffffffff800000c8 RSP=ffffffff80000000 > > So RSP was 0xffffffff80000000, a push happened, and we tried to write > to 0xffffffff7ffffff8, which failed. > >> check_exception old: 0xe new 0xe, cr2: 0xffffffff7ffffff8, rip: 0xffffffff84bb3141 >> RAX=00000000ffffffff RBX=ffffffff800000d8 RCX=ffffffff84be4021 RDX=dffffc0000000000 >> RSI=0000000000000006 RDI=ffffffff84c57000 RBP=ffffffff800000c8 RSP=ffffffff80000000 > > And #PF doesn't use IST, so it double-faulted. > > Either the stack isn't mapped in the page tables, RSP is corrupt, or > there's a genuine stack overflow here. > I reproduced this, and this is kasan bug: │0xffffffff84864897 <x86_early_init_platform_quirks+5> mov $0xffffffff83f1d0b8,%rdi │0xffffffff8486489e <x86_early_init_platform_quirks+12> movabs $0xdffffc0000000000,%rax │0xffffffff848648a8 <x86_early_init_platform_quirks+22> push %rbp │0xffffffff848648a9 <x86_early_init_platform_quirks+23> mov %rdi,%rdx │0xffffffff848648ac <x86_early_init_platform_quirks+26> shr $0x3,%rdx │0xffffffff848648b0 <x86_early_init_platform_quirks+30> mov %rsp,%rbp >│0xffffffff848648b3 <x86_early_init_platform_quirks+33> mov (%rdx,%rax,1),%al we crash on the last move which is a read from shadow (gdb) p/x $rdx $1 = 0x1ffffffff07e3a17 (gdb) p/x $rax $2 = 0xdffffc0000000000 (gdb) p/x 0xdffffc0000000000 + 0x1ffffffff07e3a17 $4 = 0xfffffbfff07e3a17 (gdb) p/x *0xfffffbfff07e3a17 Cannot access memory at address 0xfffffbfff07e3a17
