This is a note to let you know that I've just added the patch titled
m68k: Only force 030 bus error if PC not in exception table
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
m68k-only-force-030-bus-error-if-pc-not-in-exception.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 26358b8227862fc62c1ef738f21f82d2e53612e0
Author: Michael Schmitz <schmitzmic@xxxxxxxxx>
Date: Wed Mar 1 15:11:07 2023 +1300
m68k: Only force 030 bus error if PC not in exception table
[ Upstream commit e36a82bebbf7da814530d5a179bef9df5934b717 ]
__get_kernel_nofault() does copy data in supervisor mode when
forcing a task backtrace log through /proc/sysrq_trigger.
This is expected cause a bus error exception on e.g. NULL
pointer dereferencing when logging a kernel task has no
workqueue associated. This bus error ought to be ignored.
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 always
send a SEGV 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.
In contrast, both 040 and 060 access error handlers do not
care whether a fault happened on supervisor mode access,
and will call do_page_fault() on those, ultimately honoring
the exception table.
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.
I had attempted a fix for this earlier in 2019 that did rely
on testing pagefault_disabled() (see link below) to achieve
the same thing, but this patch should be more generic.
Tested on 030 Atari Falcon.
Reported-by: Eero Tamminen <oak@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/alpine.LNX.2.21.1904091023540.25@nippy.intranet
Link: https://lore.kernel.org/r/63130691-1984-c423-c1f2-73bfd8d3dcd3@xxxxxxxxx
Signed-off-by: Michael Schmitz <schmitzmic@xxxxxxxxx>
Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230301021107.26307-1-schmitzmic@xxxxxxxxx
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c
index 9b70a7f5e7058..35f706d836c50 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>
@@ -550,7 +551,8 @@ static inline void bus_error030 (struct frame *fp)
errorcode |= 2;
if (mmusr & (MMU_I | MMU_WP)) {
- if (ssw & 4) {
+ /* We might have an exception table for this PC */
+ 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,
