s390/kernel: expand exception table logic to allow new handling options

This is a s390 port of commit 548acf19234d ("x86/mm: Expand the
exception table logic to allow new handling options"), which is needed
for implementing BPF_PROBE_MEM on s390.

The new handler field is made 64-bit in order to allow pointing from
dynamically allocated entries to handlers in kernel text. Unlike on x86,
NULL is used instead of ex_handler_default. This is because exception
tables are used by boot/text_dma.S, and it would be a pain to preserve
ex_handler_default.

The new infrastructure is ignored in early_pgm_check_handler, since
there is no pt_regs.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 47 insertions, 5 deletions

diff --git a/arch/s390/include/asm/extable.h b/arch/s390/include/asm/extable.h
index ae27f756b409..3beb294fd553 100644
--- a/arch/s390/include/asm/extable.h
+++ b/arch/s390/include/asm/extable.h
@@ -1,12 +1,20 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef __S390_EXTABLE_H
 #define __S390_EXTABLE_H
+
+#include <asm/ptrace.h>
+#include <linux/compiler.h>
+
 /*
- * The exception table consists of pairs of addresses: the first is the
- * address of an instruction that is allowed to fault, and the second is
- * the address at which the program should continue.  No registers are
- * modified, so it is entirely up to the continuation code to figure out
- * what to do.
+ * The exception table consists of three addresses:
+ *
+ * - Address of an instruction that is allowed to fault.
+ * - Address at which the program should continue.
+ * - Optional address of handler that takes pt_regs * argument and runs in
+ *   interrupt context.
+ *
+ * No registers are modified, so it is entirely up to the continuation code
+ * to figure out what to do.
  *
  * All the routines below use bits of fixup code that are out of line
  * with the main instruction path.  This means when everything is well,
@@ -17,6 +25,7 @@
 struct exception_table_entry
 {
 	int insn, fixup;
+	long handler;
 };
 
 extern struct exception_table_entry *__start_dma_ex_table;
@@ -29,6 +38,39 @@ static inline unsigned long extable_fixup(const struct exception_table_entry *x)
 	return (unsigned long)&x->fixup + x->fixup;
 }
 
+typedef bool (*ex_handler_t)(const struct exception_table_entry *,
+			     struct pt_regs *);
+
+static inline ex_handler_t
+ex_fixup_handler(const struct exception_table_entry *x)
+{
+	if (likely(!x->handler))
+		return NULL;
+	return (ex_handler_t)((unsigned long)&x->handler + x->handler);
+}
+
+static inline bool ex_handle(const struct exception_table_entry *x,
+			     struct pt_regs *regs)
+{
+	ex_handler_t handler = ex_fixup_handler(x);
+
+	if (unlikely(handler))
+		return handler(x, regs);
+	regs->psw.addr = extable_fixup(x);
+	return true;
+}
+
 #define ARCH_HAS_RELATIVE_EXTABLE
 
+static inline void swap_ex_entry_fixup(struct exception_table_entry *a,
+				       struct exception_table_entry *b,
+				       struct exception_table_entry tmp,
+				       int delta)
+{
+	a->fixup = b->fixup + delta;
+	b->fixup = tmp.fixup - delta;
+	a->handler = b->handler + delta;
+	b->handler = tmp.handler - delta;
+}
+
 #endif