The patch below fixes one problem, and cleans up a wart (which didn't
really cause any problems) in head_4xx.S.
The problem was that the DSI handler would not call do_page_fault()
for zone protection faults which were writes - which meant that a user
process attempting to write to kernel (or read protected) memory would
not be SEGVed but instead would spin re-entering the exception handler
(I've confirmed this with a test program). In fact zone faults are
the only possible cause of a DSI on a read operation, so we don't need
to check whether the operation was a write.
The wart is that the ISI handler passed SRR1 (i.e. saved MSR) to
do_page_fault(), whereas the comment above do_page_fault() says that
do_page_fault() should be passed 0 for instruction faults on 4xx.
Since nothing in do_page_fault() checked any bits that mattered, it
didn't actually break anything.
diff -urN ../linuxppc_2_4_devel/arch/ppc/kernel/head_4xx.S
linux-bungo/arch/ppc/kernel/head_4xx.S
--- ../linuxppc_2_4_devel/arch/ppc/kernel/head_4xx.S Tue Sep 11 18:18:05 2001
+++ linux-bungo/arch/ppc/kernel/head_4xx.S Wed Sep 12 13:15:15 2001
@@ -221,11 +221,14 @@
mtspr SPRG7, r21
mtspr SPRG6, r22
- /* First, make sure this was a store operation.
+ /* First, check if it was a zone fault (which means a user
+ * tried to access a kernel or read-protected page - always
+ * a SEGV). All other faults here must be stores, so no
+ * need to check ESR_DST as well. */
*/
mfspr r20, SPRN_ESR
- andis. r20, r20, ESR_DST at h
- beq 2f
+ andis. r20, r20, ESR_DIZ at h
+ bne 2f
mfspr r20, SPRN_DEAR /* Get faulting address */
@@ -315,7 +318,7 @@
START_EXCEPTION(0x0400, InstructionAccess)
STND_EXCEPTION_PROLOG(0x0400)
mr r4,r22 /* Pass SRR0 as arg2 */
- mr r5,r23 /* Pass SRR1 as arg3 */
+ li r5,0
addi r3,r1,STACK_FRAME_OVERHEAD
li r7,STND_EXC
li r20,MSR_KERNEL
--
David Gibson | For every complex problem there is a
david at gibson.dropbear.id.au | solution which is simple, neat and
| wrong. -- H.L. Mencken
http://www.ozlabs.org/people/dgibson
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