On Mon, Nov 20, 2017 at 9:07 AM, Andy Lutomirski <[email protected]> wrote: > This sets up stack switching, including for SYSCALL. I think it's > in decent shape. > > Known issues: > - KASAN is likely to be busted. This could be fixed either by teaching > KASAN that cpu_entry_area contains valid stacks (I have no clue how > to go about doing this) or by rigging up the IST entry code to switch > RSP to point to the direct-mapped copy of the stacks before calling > into non-KASAN-excluded C code. >
I tried to fix the KASAN issue, and I'm doing something wrong. I'm building this tree: https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_stack&id=8319677bd04a1ab291ca71fe1da7aa023306e4a9 for 64 bits with KASAN on. The relevant commit is: https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_stack&id=a4bdb48c3469708b6b51e5ab90d27bf0c859000c If I run tools/testing/selftests/single_step_syscall_32, then the kernel goes into lala land and infinite loops. The root cause seems to we're hitting do_debug with RSP pointing into the fixmap, specifically in the cpu_entry_area's exception stack, with a value of roughly 0xffffffffff1bd108. The KASAN instrumentation in do_debug is then getting a page fault. I think my KASAN setup code should be populating the KASAN data there and, indeed, gdb seems to be able to access the faulting address. So I'm confused. Help?
