Aw: Re: kernel 4.6-rc unbootable due to module changes

Commit Message

Helge Deller April 8, 2016, 12:06 p.m. UTC

> >> So, it seems that handling exceptions from modules never worked on 
> >> pa-risc, it was just masked by the fact that exceptions from modules don't 
> >> happen during normal use.
> 
> Sadly you seem to be right :-(
> I did more testing with the test_user_copy module (with vanilla kernel 4.5 and without the relative extable support).

The attached patch fixes the exception handling for modules for me.
This is realized by saving the %r27 register in the fault handler and restoring it in the exception path.
With this patch the "test_user_copy" kernel module succeeds when loaded.
Mikulas, can you try it with your testcases ?

Helge

Patch

diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index 0abdd4c..1b05163 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -78,6 +78,7 @@  struct exception_data {
 	unsigned long fault_ip;
 	unsigned long fault_space;
 	unsigned long fault_addr;
+	unsigned long fault_gp;
 };
 
 #define __get_user(x, ptr)                               \
diff --git a/arch/parisc/kernel/asm-offsets.c b/arch/parisc/kernel/asm-offsets.c
index d2f6257..137c91e 100644
--- a/arch/parisc/kernel/asm-offsets.c
+++ b/arch/parisc/kernel/asm-offsets.c
@@ -301,6 +301,7 @@  int main(void)
 	DEFINE(EXCDATA_IP, offsetof(struct exception_data, fault_ip));
 	DEFINE(EXCDATA_SPACE, offsetof(struct exception_data, fault_space));
 	DEFINE(EXCDATA_ADDR, offsetof(struct exception_data, fault_addr));
+	DEFINE(EXCDATA_GP, offsetof(struct exception_data, fault_gp));
 	BLANK();
 	DEFINE(ASM_PDC_RESULT_SIZE, NUM_PDC_RESULT * sizeof(unsigned long));
 	BLANK();
diff --git a/arch/parisc/kernel/parisc_ksyms.c b/arch/parisc/kernel/parisc_ksyms.c
index 568b2c6..3cad8aa 100644
--- a/arch/parisc/kernel/parisc_ksyms.c
+++ b/arch/parisc/kernel/parisc_ksyms.c
@@ -47,11 +47,11 @@  EXPORT_SYMBOL(__cmpxchg_u64);
 EXPORT_SYMBOL(lclear_user);
 EXPORT_SYMBOL(lstrnlen_user);
 
-/* Global fixups */
-extern void fixup_get_user_skip_1(void);
-extern void fixup_get_user_skip_2(void);
-extern void fixup_put_user_skip_1(void);
-extern void fixup_put_user_skip_2(void);
+/* Global fixups - defined as int to avoid creation of function pointers */
+extern int fixup_get_user_skip_1;
+extern int fixup_get_user_skip_2;
+extern int fixup_put_user_skip_1;
+extern int fixup_put_user_skip_2;
 EXPORT_SYMBOL(fixup_get_user_skip_1);
 EXPORT_SYMBOL(fixup_get_user_skip_2);
 EXPORT_SYMBOL(fixup_put_user_skip_1);
diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c
index 553b098..77e2262 100644
--- a/arch/parisc/kernel/traps.c
+++ b/arch/parisc/kernel/traps.c
@@ -798,6 +798,9 @@  void notrace handle_interruption(int code, struct pt_regs *regs)
 
 	    if (fault_space == 0 && !faulthandler_disabled())
 	    {
+		/* Clean up and return if in exception table. */
+		if (fixup_exception(regs))
+			return;
 		pdc_chassis_send_status(PDC_CHASSIS_DIRECT_PANIC);
 		parisc_terminate("Kernel Fault", regs, code, fault_address);
 	    }
diff --git a/arch/parisc/lib/fixup.S b/arch/parisc/lib/fixup.S
index 536ef66..1052b74 100644
--- 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 = this_cpu_ptr(&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 = this_cpu_ptr(&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
diff --git a/arch/parisc/mm/fault.c b/arch/parisc/mm/fault.c
index a762864..245784e 100644
--- a/arch/parisc/mm/fault.c
+++ b/arch/parisc/mm/fault.c
@@ -153,6 +153,7 @@  int fixup_exception(struct pt_regs *regs)
 		d->fault_ip = regs->iaoq[0];
 		d->fault_space = regs->isr;
 		d->fault_addr = regs->ior;
+		d->fault_gp = regs->gr[27];
 
 		regs->iaoq[0] = ((fix->fixup) & ~3);
 		/*