On Mon, Sep 28, 2020 at 3:34 AM 'Dmitry Vyukov' via Clang Built Linux <[email protected]> wrote: > > On Mon, Sep 28, 2020 at 10:54 AM Borislav Petkov <[email protected]> wrote: > > > > On Mon, Sep 28, 2020 at 10:40:19AM +0200, Dmitry Vyukov wrote: > > > I meant the kernel self-corrupts itself, that just wasn't detected by > > > KASAN, page protections, etc. > > > > Well, Nick already asked this but we're marking all kernel text RO early > > during boot. So it either is happening before that or something else > > altogether is going on.
On Sun, Sep 27, 2020 at 11:06 PM 'Dmitry Vyukov' via Clang Built Linux <[email protected]> wrote: > > Interestingly there is a new crash, which looks similar: > > general protection fault in map_vdso > https://syzkaller.appspot.com/bug?extid=c2ae01c2b1b385384a06 > > The code is also with 4 0's: > Code: 00 00 00 48 b8 00 00 00 00 00 fc ff df 41 57 49 89 ff 41 56 41 > 55 41 54 55 65 48 8b 2c 25 c0 fe 01 00 48 8d bd 28 04 00 00 53 <48> 00 > 00 00 00 fa 48 83 ec 10 48 c1 ea 03 80 3c 02 00 0f 85 51 02 > > But it happened with gcc. > > Also I found this older one: > general protection fault in map_vdso_randomized > https://syzkaller.appspot.com/bug?id=8366fd024559946137b9db23b26fd2235d43b383 > > which also has code smashed and happened with gcc: > Code: 00 fc ff df 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 eb 00 00 00 > 65 48 8b 1c 25 c0 fe 01 00 48 8d bb 28 04 00 00 41 2b 54 24 20 <00> 00 > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 If this is related to vdso's, they seem mapped as `r-xp` (not `w): $ sudo cat /proc/1/maps | grep vdso 7ffc667f5000-7ffc667f7000 r-xp 00000000 00:00 0 [vdso] map_vdso() in arch/x86/entry/vdso/vma.c doesn't map the VMA as writable, but it uses VM_MAYWRITE with a comment about GDB setting breakpoints. So it sounds like the page protections on the vdso can be changed at runtime (via mprotect). Maybe syzkaller is tickling that first? map_vdso_randomized() does call map_vdso(). Maybe if we mprotect the vdso to be writable, it may be easier to spot the write. -- Thanks, ~Nick Desaulniers
