PERFORCE change 985521 for review

[Robert Watson]

http://p4web.freebsd.org/@@985521?ac=10

Change 985521 by rwatson at rwatson_zenith_cl_cam_ac_uk on 2013/10/06 20:39:27

	Correct a CCall exception-handler bug in PC bounds checking.
	
	When an error is encountered in CCall or CReturn, jump to the
	general-purpose userspace exception handler code.  Until we can
	set the capability cause register, this will incorrectly report
	the error as a CCall/CReturn exception rather than as the
	particular failure detected and handled, but this is better
	than continuing blindly and failing to report (or describe) the
	problem.

Affected files ...

.. //depot/projects/ctsrd/cheribsd/src/sys/mips/cheri/ccall.S#11 edit

Differences ...

==== //depot/projects/ctsrd/cheribsd/src/sys/mips/cheri/ccall.S#11 (text+ko) ====

@@ -104,11 +104,8 @@
  * instruction to extract the capabilities to fixed ones targetable in
  * assembly and by the compiler.
  *
- * XXXRW: Lots of non-done checking -- e.g., types, protection bits, etc.  We
- * need a C error-handling path.
- *
- * XXXRW: We'd like a CSetCause so that we can jump to the general CP2
- * exception handler from here after setting its state appropriately.
+ * XXXRW: We'd like a CSetCause so that the general CP2 exception handling
+ * code can pick up the pieces cleanly.
  *
  * NB: No attempt to make this pipeline well yet -- branch-delay slots not
  * well-utilised, some CP2 fields accessed multiple times.
@@ -165,7 +162,7 @@
 	PTR_ADDU	k0, k0, k1
 	PTR_SUBIU	k0, 4
 	cgettype	k1, CHERI_REG_CCALLCODE
-	sltu		k1, k1, k0
+	sltu		k1, k0, k1
 	bnez		k1, CCall_c1_range
 	nop
 
@@ -253,13 +250,13 @@
 CCall_c1_perms:
 CCall_c1_range:
 CCall_stack_overflow:
-	/* XXXRW: For now, treat as a NOP. */
-	MFC0		k0, MIPS_COP_0_EXC_PC
-	PTR_ADDIU	k0, 4
-	MTC0		k0, MIPS_COP_0_EXC_PC
-
-	CHERI_EXCEPTION_RETURN(k0);
-	eret
+	/*
+	 * XXXRW: We would very much like to use CSetCause here to insert the
+	 * right cause for the failure mode detected ... but CHERI doesn't yet
+	 * support that.
+	 */
+	j	_C_LABEL(MipsUserGenException)
+	nop
 
         .set pop
 
@@ -267,15 +264,12 @@
  * Software implementation of CReturn; this code does not need to be position-
  * independent as it is not relocated to an exception vector.
  *
- * XXXRW: Lots of non-done checking -- e.g., types, protection bits, etc.  We
- * need a C error handling path.
- *
- * XXXRW: We'd like a CSetCause so that we can jump to the general CP2
- * exception handler from here after setting its state appropriately.
+ * XXXRW: We'd like a CSetCause so that the general CP2 exception handling
+ * code can pick up the pieces cleanly.
  *
  * Possible failure modes:
  *
- * 1. Trusted stack underflow.   XXXRW: How to deal with this?
+ * 1. Trusted stack underflow.
  */
 CHERICReturn:
         .set push
@@ -328,12 +322,12 @@
 	eret
 
 CReturn_stack_underflow:
-	/* XXXRW: For now, treat as a NOP. */
-	MFC0		k0, MIPS_COP_0_EXC_PC
-	PTR_ADDIU	k0, 4
-	MTC0		k0, MIPS_COP_0_EXC_PC
-
-	CHERI_EXCEPTION_RETURN(k0)
-	eret
+	/*
+	 * XXXRW: We would very much like to use CSetCause here to insert the
+	 * right cause for the failure mode detected ... but CHERI doesn't yet
+	 * support that.
+	 */
+	j	_C_LABEL(MipsUserGenException)
+	nop
 
 	.set pop