powerpc: Set regs->dar if memory access fails in emulate_step()

This adds code to the instruction emulation code to set regs->dar
to the address of any memory access that fails.  This address is
not necessarily the same as the effective address of the instruction,
because if the memory access is unaligned, it might cross a page
boundary and fault on the second page.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/sstep.c

@@ -103,11 +103,19 @@ static nokprobe_inline int branch_taken(unsigned int instr,
 	return 1;
 }
 
-static nokprobe_inline long address_ok(struct pt_regs *regs, unsigned long ea, int nb)
+static nokprobe_inline long address_ok(struct pt_regs *regs,
+				       unsigned long ea, int nb)
 {
 	if (!user_mode(regs))
 		return 1;
-	return __access_ok(ea, nb, USER_DS);
+	if (__access_ok(ea, nb, USER_DS))
+		return 1;
+	if (__access_ok(ea, 1, USER_DS))
+		/* Access overlaps the end of the user region */
+		regs->dar = USER_DS.seg;
+	else
+		regs->dar = ea;
+	return 0;
 }
 
 /*
@@ -210,7 +218,8 @@ static nokprobe_inline unsigned long byterev_8(unsigned long x)
 #endif
 
 static nokprobe_inline int read_mem_aligned(unsigned long *dest,
-					unsigned long ea, int nb)
+					    unsigned long ea, int nb,
+					    struct pt_regs *regs)
 {
 	int err = 0;
 	unsigned long x = 0;
@@ -233,6 +242,8 @@ static nokprobe_inline int read_mem_aligned(unsigned long *dest,
 	}
 	if (!err)
 		*dest = x;
+	else
+		regs->dar = ea;
 	return err;
 }
 
@@ -240,7 +251,8 @@ static nokprobe_inline int read_mem_aligned(unsigned long *dest,
  * Copy from userspace to a buffer, using the largest possible
  * aligned accesses, up to sizeof(long).
  */
-static int nokprobe_inline copy_mem_in(u8 *dest, unsigned long ea, int nb)
+static int nokprobe_inline copy_mem_in(u8 *dest, unsigned long ea, int nb,
+				       struct pt_regs *regs)
 {
 	int err = 0;
 	int c;
@@ -268,8 +280,10 @@ static int nokprobe_inline copy_mem_in(u8 *dest, unsigned long ea, int nb)
 			break;
 #endif
 		}
-		if (err)
+		if (err) {
+			regs->dar = ea;
 			return err;
+		}
 		dest += c;
 		ea += c;
 	}
@@ -289,7 +303,7 @@ static nokprobe_inline int read_mem_unaligned(unsigned long *dest,
 
 	u.ul = 0;
 	i = IS_BE ? sizeof(unsigned long) - nb : 0;
-	err = copy_mem_in(&u.b[i], ea, nb);
+	err = copy_mem_in(&u.b[i], ea, nb, regs);
 	if (!err)
 		*dest = u.ul;
 	return err;
@@ -306,13 +320,14 @@ static int read_mem(unsigned long *dest, unsigned long ea, int nb,
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
 	if ((ea & (nb - 1)) == 0)
-		return read_mem_aligned(dest, ea, nb);
+		return read_mem_aligned(dest, ea, nb, regs);
 	return read_mem_unaligned(dest, ea, nb, regs);
 }
 NOKPROBE_SYMBOL(read_mem);
 
 static nokprobe_inline int write_mem_aligned(unsigned long val,
-					unsigned long ea, int nb)
+					     unsigned long ea, int nb,
+					     struct pt_regs *regs)
 {
 	int err = 0;
 
@@ -332,6 +347,8 @@ static nokprobe_inline int write_mem_aligned(unsigned long val,
 		break;
 #endif
 	}
+	if (err)
+		regs->dar = ea;
 	return err;
 }
 
@@ -339,7 +356,8 @@ static nokprobe_inline int write_mem_aligned(unsigned long val,
  * Copy from a buffer to userspace, using the largest possible
  * aligned accesses, up to sizeof(long).
  */
-static int nokprobe_inline copy_mem_out(u8 *dest, unsigned long ea, int nb)
+static int nokprobe_inline copy_mem_out(u8 *dest, unsigned long ea, int nb,
+					struct pt_regs *regs)
 {
 	int err = 0;
 	int c;
@@ -367,8 +385,10 @@ static int nokprobe_inline copy_mem_out(u8 *dest, unsigned long ea, int nb)
 			break;
 #endif
 		}
-		if (err)
+		if (err) {
+			regs->dar = ea;
 			return err;
+		}
 		dest += c;
 		ea += c;
 	}
@@ -387,7 +407,7 @@ static nokprobe_inline int write_mem_unaligned(unsigned long val,
 
 	u.ul = val;
 	i = IS_BE ? sizeof(unsigned long) - nb : 0;
-	return copy_mem_out(&u.b[i], ea, nb);
+	return copy_mem_out(&u.b[i], ea, nb, regs);
 }
 
 /*
@@ -400,7 +420,7 @@ static int write_mem(unsigned long val, unsigned long ea, int nb,
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
 	if ((ea & (nb - 1)) == 0)
-		return write_mem_aligned(val, ea, nb);
+		return write_mem_aligned(val, ea, nb, regs);
 	return write_mem_unaligned(val, ea, nb, regs);
 }
 NOKPROBE_SYMBOL(write_mem);
@@ -422,7 +442,7 @@ static int do_fp_load(int rn, unsigned long ea, int nb, struct pt_regs *regs)
 
 	if (!address_ok(regs, ea, nb))
 		return -EFAULT;
-	err = copy_mem_in(u.b, ea, nb);
+	err = copy_mem_in(u.b, ea, nb, regs);
 	if (err)
 		return err;
 	preempt_disable();
@@ -471,7 +491,7 @@ static int do_fp_store(int rn, unsigned long ea, int nb, struct pt_regs *regs)
 			u.l[1] = current->thread.TS_FPR(rn);
 	}
 	preempt_enable();
-	return copy_mem_out(u.b, ea, nb);
+	return copy_mem_out(u.b, ea, nb, regs);
 }
 NOKPROBE_SYMBOL(do_fp_store);
 #endif
@@ -491,7 +511,7 @@ static nokprobe_inline int do_vec_load(int rn, unsigned long ea,
 		return -EFAULT;
 	/* align to multiple of size */
 	ea &= ~(size - 1);
-	err = copy_mem_in(&u.b[ea & 0xf], ea, size);
+	err = copy_mem_in(&u.b[ea & 0xf], ea, size, regs);
 	if (err)
 		return err;
 
@@ -523,7 +543,7 @@ static nokprobe_inline int do_vec_store(int rn, unsigned long ea,
 	else
 		u.v = current->thread.vr_state.vr[rn];
 	preempt_enable();
-	return copy_mem_out(&u.b[ea & 0xf], ea, size);
+	return copy_mem_out(&u.b[ea & 0xf], ea, size, regs);
 }
 #endif /* CONFIG_ALTIVEC */
 
@@ -725,7 +745,7 @@ static nokprobe_inline int do_vsx_load(struct instruction_op *op,
 	union vsx_reg buf;
 	int size = GETSIZE(op->type);
 
-	if (!address_ok(regs, ea, size) || copy_mem_in(mem, ea, size))
+	if (!address_ok(regs, ea, size) || copy_mem_in(mem, ea, size, regs))
 		return -EFAULT;
 
 	emulate_vsx_load(op, &buf, mem);
@@ -776,7 +796,7 @@ static nokprobe_inline int do_vsx_store(struct instruction_op *op,
 	}
 	preempt_enable();
 	emulate_vsx_store(op, &buf, mem);
-	return  copy_mem_out(mem, ea, size);
+	return  copy_mem_out(mem, ea, size, regs);
 }
 #endif /* CONFIG_VSX */
 
@@ -797,8 +817,10 @@ int emulate_dcbz(unsigned long ea, struct pt_regs *regs)
 		return -EFAULT;
 	for (i = 0; i < size; i += sizeof(long)) {
 		err = __put_user(0, (unsigned long __user *) (ea + i));
-		if (err)
+		if (err) {
+			regs->dar = ea;
 			return err;
+		}
 	}
 	return 0;
 }
@@ -2640,8 +2662,10 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 			err = emulate_dcbz(ea, regs);
 			break;
 		}
-		if (err)
+		if (err) {
+			regs->dar = ea;
 			return 0;
+		}
 		goto instr_done;
 
 	case LARX:
@@ -2668,12 +2692,16 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 			break;
 		case 16:
 			err = do_lqarx(ea, &regs->gpr[op.reg]);
-			goto ldst_done;
+			break;
 #endif
 		default:
 			return 0;
 		}
-		if (!err)
+		if (err) {
+			regs->dar = ea;
+			return 0;
+		}
+		if (size < 16)
 			regs->gpr[op.reg] = val;
 		goto ldst_done;
 
@@ -2711,6 +2739,8 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
 			regs->ccr = (regs->ccr & 0x0fffffff) |
 				(cr & 0xe0000000) |
 				((regs->xer >> 3) & 0x10000000);
+		else
+			regs->dar = ea;
 		goto ldst_done;
 
 	case LOAD: