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

[Michael Schmitz <schmitzmic@gmail.com>]

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@gmail.com># Please enter
>> the commit message for your changes. Lines starting
>> CC: Eero Tamminen <oak@helsinkinet.fi>
>> CC: Finn Thain <ftain@linux-m68k.org>
>> CC: Andreas Schwab <schwab@linux-m68k.org>
>> CC: Geert Uytterhoeven <geert@linux-m68k.org>
>> Link:
>> https://lore.kernel.org/r/daca2f68-19fa-a2b6-97c6-16b5b7e26afe@helsinkinet.fi
>>
>> ---
>>   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,