Re: [PATCH RFC v1] m68k: kernel/traps.c - only force 030 bus error if PC not in exception table

[Michael Schmitz <schmitzmic@xxxxxxxxx>]

Thanks Eero,

I'll add your Tested-by (and Reported-by; sorry to have forgotten that) 
in v2.

Cheers,

	Michael


Am 24.02.2023 um 13:31 schrieb Eero Tamminen:
> Hi Michael,
>
> On 22.2.2023 21.50, Michael Schmitz wrote:
> > __get_kernel_nofault() does copy data in supervisor mode when
> > forcing a task backtrace dump through the sysrq trigger.
> >
> > Our 030 bus error handler is ill equipped to deal with this:
> >
> > Whenever ssw indicates a kernel mode access on a data fault,
> > we don't even attempt to handle the fault and instead send
> > a bus error signal (or panic). As a result, the check for
> > exception handling at the fault PC (buried in send_sig_fault()
> > which gets called from do_page_fault() eventually) is never
> > used.
> >
> > Both 040 and 060 access error handlers do not care whether
> > a fault happened on supervisor mode access, and will call
> > do_page_fault() even on those.
> >
> > Add a check in bus_error030 to call do_page_fault() in case
> > we do have an entry for the fault PC in our exception table.
> >
> > Tested on 030 Atari Falcon.
>
>
> I've verified that the kernel Oops was there with unpatched kernel, and
> this fixes it, also when using Hatari emulator 030 / Atari Falcon
> emulation.
>
> (Verified both with both v6.0 & v6.2 of Linus' kernel sources.)
>
>
>     - Eero
>
>
> > Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx># Please enter
> > the commit message for your changes. Lines starting
> > CC: Eero Tamminen <oak@xxxxxxxxxxxxxx>
> > CC: Finn Thain <ftain@xxxxxxxxxxxxxx>
> > CC: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
> > CC: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> > Link:
> > https://lore.kernel.org/r/daca2f68-19fa-a2b6-97c6-16b5b7e26afe@xxxxxxxxxxxxxx
> >
> > ---
> >   arch/m68k/kernel/traps.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
> > index 5c8cba0efc63..67576fb0c466 100644
> > --- a/arch/m68k/kernel/traps.c
> > +++ b/arch/m68k/kernel/traps.c
> > @@ -30,6 +30,7 @@
> >   #include <linux/init.h>
> >   #include <linux/ptrace.h>
> >   #include <linux/kallsyms.h>
> > +#include <linux/extable.h>
> >     #include <asm/setup.h>
> >   #include <asm/fpu.h>
> > @@ -545,7 +546,7 @@ static inline void bus_error030 (struct frame *fp)
> >               errorcode |= 2;
> >             if (mmusr & (MMU_I | MMU_WP)) {
> > -            if (ssw & 4) {
> > +            if (ssw & 4 && !search_exception_tables(fp->ptregs.pc)) {
> >                   pr_err("Data %s fault at %#010lx in %s (pc=%#lx)\n",
> >                          ssw & RW ? "read" : "write",
> >                          fp->un.fmtb.daddr,