parisc: Clear stale IIR value on instruction access rights trap

When a trap 7 (Instruction access rights) occurs, this means the CPU couldn't execute an instruction due to missing execute permissions on the memory region. In this case it seems the CPU didn't even fetched the instruction from memory and thus did not store it in the cr19 (IIR) register before calling the trap handler. So, the trap handler will find some random old stale value in cr19. This patch simply overwrites the stale IIR value with a constant magic "bad food" value (0xbaadf00d), in the hope people don't start to try to understand the various random IIR values in trap 7 dumps. Noticed-by: John David Anglin <[email protected]> Signed-off-by: Helge Deller <[email protected]>
tadfisher · Dec 20, 2021 · 484730e · 484730e
1 parent a7904a5
commit 484730e
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
@@ -730,6 +730,8 @@ void notrace handle_interruption(int code, struct pt_regs *regs)
 			}
 			mmap_read_unlock(current->mm);
 		}
+		/* CPU could not fetch instruction, so clear stale IIR value. */
+		regs->iir = 0xbaadf00d;
 		fallthrough;
 	case 27: 
 		/* Data memory protection ID trap */