From: Michael Schmitz schmitzmic@gmail.com
[ 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@helsinkinet.fi 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@gmail.com Signed-off-by: Michael Schmitz schmitzmic@gmail.com Reviewed-by: Geert Uytterhoeven geert@linux-m68k.org Link: https://lore.kernel.org/r/20230301021107.26307-1-schmitzmic@gmail.com Signed-off-by: Geert Uytterhoeven geert@linux-m68k.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/m68k/kernel/traps.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/m68k/kernel/traps.c b/arch/m68k/kernel/traps.c index a245c1933d418..5bf314871e9f6 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,