m68k: Disable/restore interrupts in hwreg_present()/hwreg_write()

hwreg_present() and hwreg_write() temporarily change the VBR register to
another vector table. This table contains a valid bus error handler
only, all other entries point to arbitrary addresses.

If an interrupt comes in while the temporary table is active, the
processor will start executing at such an arbitrary address, and the
kernel will crash.

While most callers run early, before interrupts are enabled, or
explicitly disable interrupts, Finn Thain pointed out that macsonic has
one callsite that doesn't, causing intermittent boot crashes.
There's another unsafe callsite in hilkbd.

Fix this for good by disabling and restoring interrupts inside
hwreg_present() and hwreg_write().

Explicitly disabling interrupts can be removed from the callsites later.

Reported-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/m68k/mm/hwtest.c b/arch/m68k/mm/hwtest.c
index 2c7dde3c6430..2a5259fd23eb 100644
--- a/arch/m68k/mm/hwtest.c
+++ b/arch/m68k/mm/hwtest.c
@@ -28,9 +28,11 @@
 int hwreg_present( volatile void *regp )
 {
     int ret = 0;
+    unsigned long flags;
     long        save_sp, save_vbr;
     long        tmp_vectors[3];
 
+    local_irq_save(flags);
     __asm__ __volatile__
         (       "movec  %/vbr,%2\n\t"
                 "movel  #Lberr1,%4@(8)\n\t"
@@ -46,6 +48,7 @@ int hwreg_present( volatile void *regp )
                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
                 : "a" (regp), "a" (tmp_vectors)
                 );
+    local_irq_restore(flags);
 
     return( ret );
 }
@@ -58,9 +61,11 @@ EXPORT_SYMBOL(hwreg_present);
 int hwreg_write( volatile void *regp, unsigned short val )
 {
         int             ret;
+        unsigned long flags;
         long    save_sp, save_vbr;
         long    tmp_vectors[3];
 
+        local_irq_save(flags);
         __asm__ __volatile__
         (       "movec  %/vbr,%2\n\t"
                 "movel  #Lberr2,%4@(8)\n\t"
@@ -78,6 +83,7 @@ int hwreg_write( volatile void *regp, unsigned short val )
                 : "=&d" (ret), "=&r" (save_sp), "=&r" (save_vbr)
                 : "a" (regp), "a" (tmp_vectors), "g" (val)
         );
+        local_irq_restore(flags);
 
         return( ret );
 }