Merge tag 's390-7.0-6' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

Pull s390 fixes from Vasily Gorbik:

 - Add array_index_nospec() to syscall dispatch table lookup to prevent
   limited speculative out-of-bounds access with user-controlled syscall
   number

 - Mark array_index_mask_nospec() __always_inline since GCC may emit an
   out-of-line call instead of the inline data dependency sequence the
   mitigation relies on

 - Clear r12 on kernel entry to prevent potential speculative use of
   user value in system_call, ext/io/mcck interrupt handlers

* tag 's390-7.0-6' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux:
  s390/entry: Scrub r12 register on kernel entry
  s390/syscalls: Add spectre boundary for syscall dispatch table
  s390/barrier: Make array_index_mask_nospec() __always_inline

Author: torvalds

arch/s390/include/asm/barrier.h

@@ -62,8 +62,8 @@ do {									\
  * @size: number of elements in array
  */
 #define array_index_mask_nospec array_index_mask_nospec
-static inline unsigned long array_index_mask_nospec(unsigned long index,
-						    unsigned long size)
+static __always_inline unsigned long array_index_mask_nospec(unsigned long index,
+							     unsigned long size)
 {
 	unsigned long mask;
 

arch/s390/kernel/entry.S

@@ -271,6 +271,7 @@ SYM_CODE_START(system_call)
 	xgr	%r9,%r9
 	xgr	%r10,%r10
 	xgr	%r11,%r11
+	xgr	%r12,%r12
 	la	%r2,STACK_FRAME_OVERHEAD(%r15)	# pointer to pt_regs
 	mvc	__PT_R8(64,%r2),__LC_SAVE_AREA(%r13)
 	MBEAR	%r2,%r13
@@ -407,6 +408,7 @@ SYM_CODE_START(\name)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA(%r13)
 	MBEAR	%r11,%r13
@@ -496,6 +498,7 @@ SYM_CODE_START(mcck_int_handler)
 	xgr	%r6,%r6
 	xgr	%r7,%r7
 	xgr	%r10,%r10
+	xgr	%r12,%r12
 	stmg	%r8,%r9,__PT_PSW(%r11)
 	xc	__PT_FLAGS(8,%r11),__PT_FLAGS(%r11)
 	xc	__SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15)

arch/s390/kernel/syscall.c

@@ -13,6 +13,7 @@
  */
 
 #include <linux/cpufeature.h>
+#include <linux/nospec.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
@@ -131,8 +132,10 @@ void noinstr __do_syscall(struct pt_regs *regs, int per_trap)
 	if (unlikely(test_and_clear_pt_regs_flag(regs, PIF_SYSCALL_RET_SET)))
 		goto out;
 	regs->gprs[2] = -ENOSYS;
-	if (likely(nr < NR_syscalls))
+	if (likely(nr < NR_syscalls)) {
+		nr = array_index_nospec(nr, NR_syscalls);
 		regs->gprs[2] = sys_call_table[nr](regs);
+	}
 out:
 	syscall_exit_to_user_mode(regs);
 }