[PATCH 3.16 178/217] parisc: Unbreak handling exceptions from kernel modules

[Ben Hutchings]

3.16.35-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Helge Deller <deller@xxxxxx>

commit 2ef4dfd9d9f288943e249b78365a69e3ea3ec072 upstream.

Handling exceptions from modules never worked on parisc.
It was just masked by the fact that exceptions from modules
don't happen during normal use.

When a module triggers an exception in get_user() we need to load the
main kernel dp value before accessing the exception_data structure, and
afterwards restore the original dp value of the module on exit.

Noticed-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Helge Deller <deller@xxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/parisc/include/asm/uaccess.h | 1 +
 arch/parisc/kernel/asm-offsets.c  | 1 +
 arch/parisc/lib/fixup.S           | 6 ++++++
 arch/parisc/mm/fault.c            | 1 +
 4 files changed, 9 insertions(+)

--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -79,6 +79,7 @@ struct exception_table_entry {
  */
 struct exception_data {
 	unsigned long fault_ip;
+	unsigned long fault_gp;
 	unsigned long fault_space;
 	unsigned long fault_addr;
 };
--- a/arch/parisc/kernel/asm-offsets.c
+++ b/arch/parisc/kernel/asm-offsets.c
@@ -292,6 +292,7 @@ int main(void)
 	DEFINE(ASM_PT_INITIAL, PT_INITIAL);
 	BLANK();
 	DEFINE(EXCDATA_IP, offsetof(struct exception_data, fault_ip));
+	DEFINE(EXCDATA_GP, offsetof(struct exception_data, fault_gp));
 	DEFINE(EXCDATA_SPACE, offsetof(struct exception_data, fault_space));
 	DEFINE(EXCDATA_ADDR, offsetof(struct exception_data, fault_addr));
 	BLANK();
--- a/arch/parisc/lib/fixup.S
+++ b/arch/parisc/lib/fixup.S
@@ -26,6 +26,7 @@
 
 #ifdef CONFIG_SMP
 	.macro  get_fault_ip t1 t2
+	loadgp
 	addil LT%__per_cpu_offset,%r27
 	LDREG RT%__per_cpu_offset(%r1),\t1
 	/* t2 = smp_processor_id() */
@@ -40,14 +41,19 @@
 	LDREG RT%exception_data(%r1),\t1
 	/* t1 = &__get_cpu_var(exception_data) */
 	add,l \t1,\t2,\t1
+	/* %r27 = t1->fault_gp - restore gp */
+	LDREG EXCDATA_GP(\t1), %r27
 	/* t1 = t1->fault_ip */
 	LDREG EXCDATA_IP(\t1), \t1
 	.endm
 #else
 	.macro  get_fault_ip t1 t2
+	loadgp
 	/* t1 = &__get_cpu_var(exception_data) */
 	addil LT%exception_data,%r27
 	LDREG RT%exception_data(%r1),\t2
+	/* %r27 = t2->fault_gp - restore gp */
+	LDREG EXCDATA_GP(\t2), %r27
 	/* t1 = t2->fault_ip */
 	LDREG EXCDATA_IP(\t2), \t1
 	.endm
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -151,6 +151,7 @@ int fixup_exception(struct pt_regs *regs
 		struct exception_data *d;
 		d = this_cpu_ptr(&exception_data);
 		d->fault_ip = regs->iaoq[0];
+		d->fault_gp = regs->gr[27];
 		d->fault_space = regs->isr;
 		d->fault_addr = regs->ior;