On Sat, Jun 13, 2015 at 12:03 AM, Ingo Molnar <[email protected]> wrote: > > * Brian Gerst <[email protected]> wrote: > >> On Fri, Jun 12, 2015 at 4:36 AM, Ingo Molnar <[email protected]> wrote: >> > >> > * H. Peter Anvin <[email protected]> wrote: >> > >> >> %es is used implicitly by string instructions. >> > >> > Ok, so we are probably better off reloading ES as well early, right >> > when we return from the firmware, just in case something does >> > a copy before we hit the ES restore in restore_processor_state(), >> > which is a generic C function? >> > >> > Something like the patch below? >> > >> > I also added FS/GS/SS reloading to make it complete. If this (or a variant >> > thereof, it's still totally untested) works then we can remove the segment >> > save/restore layer in __save/restore_processor_state(). >> > >> > Thanks, >> > >> > Ingo >> > >> > ===========> >> > arch/x86/kernel/acpi/wakeup_32.S | 13 +++++++++++++ >> > 1 file changed, 13 insertions(+) >> > >> > diff --git a/arch/x86/kernel/acpi/wakeup_32.S >> > b/arch/x86/kernel/acpi/wakeup_32.S >> > index 665c6b7d2ea9..1376a7fc21b7 100644 >> > --- a/arch/x86/kernel/acpi/wakeup_32.S >> > +++ b/arch/x86/kernel/acpi/wakeup_32.S >> > @@ -61,6 +61,19 @@ ENTRY(wakeup_pmode_return) >> > >> > >> > restore_registers: >> > + /* >> > + * In case the BIOS corrupted our segment descriptors, >> > + * reload them to clear out any shadow descriptor >> > + * state: >> > + */ >> > + movl $__USER_DS, %eax >> > + movl %eax, %ds >> > + movl %eax, %es >> > + movl %eax, %fs >> > + movl %eax, %gs >> > + movl $__KERNEL_DS, %eax >> > + movl %eax, %ss >> > + >> > movl saved_context_ebp, %ebp >> > movl saved_context_ebx, %ebx >> > movl saved_context_esi, %esi >> >> If you follow the convoluted flow of the calls in this file, >> wakeup_pmode_return >> is the first thing called from the trampoline on resume, and that loads the >> data >> segments with __KERNEL_DS. [...] > > So if wakeup_pmode_return is really the first thing called then the whole > premise > of shadow descriptor corruption goes out the window: we reload all relevant > segment registers.
True, but it still leaves the fact that we're loading __KERNEL_DS instead of __USER_DS, right? So we end up in the kernel in some context (I have no clue what context) with __KERNEL_DS loaded. It's very easy for us to inadvertently fix it: we could return to userspace by any means whatsoever except SYSEXIT, or we could even return back to some preempted kernel context. I still think we should replace __KERNEL_DS with __USER_DS in wakeup_pmode_return and see if the problem goes away. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
