s390: fix __EMIT_BUG() macro

Setting a kprobe on getname_flags() failed:

$ echo 'p:tmr1 getname_flags +0(%r2):ustring' > kprobe_events
-bash: echo: write error: Invalid argument

Debugging the kprobes code showed that the address of
getname_flags() is contained in the __bug_table. Kprobes
doesn't allow to set probes at BUG() locations.

$ objdump -j  __bug_table -x build/fs/namei.o
[..]
0000000000000108 R_390_PC32        .text+0x00000000000075a8
000000000000010c R_390_PC32        .L223+0x0000000000000004

I was expecting getname_flags() to start with a BUG(), but:

7598:       e3 20 10 00 00 04       lg      %r2,0(%r1)
759e:       c0 f4 00 00 00 00       jg      759e <putname+0x7e>
75a0: R_390_PLT32DBL    kmem_cache_free+0x2
75a4:       a7 f4 00 01             j       75a6 <putname+0x86>

00000000000075a8 <getname_flags>:
75a8:       c0 04 00 00 00 00       brcl    0,75a8 <getname_flags>
75ae:       eb 6f f0 48 00 24       stmg    %r6,%r15,72(%r15)
75b4:       b9 04 00 ef             lgr     %r14,%r15
75b8:       e3 f0 ff a8 ff 71       lay     %r15,-88(%r15)

So the BUG() is actually the last opcode of the previous function.
Fix this by switching to using the MONITOR CALL (MC) instruction,
and set the entry in __bug_table to the beginning of that MC.

Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/boot/head.S b/arch/s390/boot/head.S
index 4b86a8d3c1219a4528bf4f0e1bba9fac2788ae06..dae10961d07246cc5a49dd80cefa8f79697056c7 100644 (file)
--- a/arch/s390/boot/head.S
+++ b/arch/s390/boot/head.S
@@ -329,7 +329,7 @@ ENTRY(startup_kdump)
        .quad   .Lduct                  # cr5: primary-aste origin
        .quad   0                       # cr6:  I/O interrupts
        .quad   0                       # cr7:  secondary space segment table
-       .quad   0                       # cr8:  access registers translation
+       .quad   0x0000000000008000      # cr8:  access registers translation
        .quad   0                       # cr9:  tracing off
        .quad   0                       # cr10: tracing off
        .quad   0                       # cr11: tracing off

diff --git a/arch/s390/include/asm/bug.h b/arch/s390/include/asm/bug.h
index a2b11ac00f6079ed102c9c675dbb4dd45ee76843..7725f8006fdfb32a9b60b06a6f70c4954f1edafb 100644 (file)
--- a/arch/s390/include/asm/bug.h
+++ b/arch/s390/include/asm/bug.h
@@ -10,15 +10,14 @@
 
 #define __EMIT_BUG(x) do {                                     \
        asm_inline volatile(                                    \
-               "0:     j       0b+2\n"                         \
-               "1:\n"                                          \
+               "0:     mc      0,0\n"                          \
                ".section .rodata.str,\"aMS\",@progbits,1\n"    \
-               "2:     .asciz  \""__FILE__"\"\n"               \
+               "1:     .asciz  \""__FILE__"\"\n"               \
                ".previous\n"                                   \
                ".section __bug_table,\"awM\",@progbits,%2\n"   \
-               "3:     .long   1b-3b,2b-3b\n"                  \
+               "2:     .long   0b-2b,1b-2b\n"                  \
                "       .short  %0,%1\n"                        \
-               "       .org    3b+%2\n"                        \
+               "       .org    2b+%2\n"                        \
                ".previous\n"                                   \
                : : "i" (__LINE__),                             \
                    "i" (x),                                    \
@@ -29,12 +28,11 @@
 
 #define __EMIT_BUG(x) do {                                     \
        asm_inline volatile(                                    \
-               "0:     j       0b+2\n"                         \
-               "1:\n"                                          \
+               "0:     mc      0,0\n"                          \
                ".section __bug_table,\"awM\",@progbits,%1\n"   \
-               "2:     .long   1b-2b\n"                        \
+               "1:     .long   0b-1b\n"                        \
                "       .short  %0\n"                           \
-               "       .org    2b+%1\n"                        \
+               "       .org    1b+%1\n"                        \
                ".previous\n"                                   \
                : : "i" (x),                                    \
                    "i" (sizeof(struct bug_entry)));            \

diff --git a/arch/s390/kernel/entry.h b/arch/s390/kernel/entry.h
index b2956d49b6ad76be0ce50d5dd51d81796b96f00c..1d3927e01a5fd693d3e8d9b9cf06cf972b87db2a 100644 (file)
--- a/arch/s390/kernel/entry.h
+++ b/arch/s390/kernel/entry.h
@@ -45,6 +45,7 @@ void specification_exception(struct pt_regs *regs);
 void transaction_exception(struct pt_regs *regs);
 void translation_exception(struct pt_regs *regs);
 void vector_exception(struct pt_regs *regs);
+void monitor_event_exception(struct pt_regs *regs);
 
 void do_per_trap(struct pt_regs *regs);
 void do_report_trap(struct pt_regs *regs, int si_signo, int si_code, char *str);

diff --git a/arch/s390/kernel/pgm_check.S b/arch/s390/kernel/pgm_check.S
index 59dee9d3bebf145aba71d6a2b164823294dad8f5..eee3a482195a6526d23c0dd89d5af8fe1deb5bf5 100644 (file)
--- a/arch/s390/kernel/pgm_check.S
+++ b/arch/s390/kernel/pgm_check.S
@@ -81,7 +81,7 @@ PGM_CHECK_DEFAULT                     /* 3c */
 PGM_CHECK_DEFAULT                      /* 3d */
 PGM_CHECK_DEFAULT                      /* 3e */
 PGM_CHECK_DEFAULT                      /* 3f */
-PGM_CHECK_DEFAULT                      /* 40 */
+PGM_CHECK(monitor_event_exception)     /* 40 */
 PGM_CHECK_DEFAULT                      /* 41 */
 PGM_CHECK_DEFAULT                      /* 42 */
 PGM_CHECK_DEFAULT                      /* 43 */

diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c
index 164c0282b41ae62df2498b8082d6cabf9f40d975..dc75588d789432049983ec47969b58fd28d51bc1 100644 (file)
--- a/arch/s390/kernel/traps.c
+++ b/arch/s390/kernel/traps.c
@@ -53,11 +53,6 @@ void do_report_trap(struct pt_regs *regs, int si_signo, int si_code, char *str)
                 if (fixup)
                        regs->psw.addr = extable_fixup(fixup);
                else {
-                       enum bug_trap_type btt;
-
-                       btt = report_bug(regs->psw.addr, regs);
-                       if (btt == BUG_TRAP_TYPE_WARN)
-                               return;
                        die(regs, str);
                }
         }
@@ -245,6 +240,27 @@ void space_switch_exception(struct pt_regs *regs)
        do_trap(regs, SIGILL, ILL_PRVOPC, "space switch event");
 }
 
+void monitor_event_exception(struct pt_regs *regs)
+{
+       const struct exception_table_entry *fixup;
+
+       if (user_mode(regs))
+               return;
+
+       switch (report_bug(regs->psw.addr - (regs->int_code >> 16), regs)) {
+       case BUG_TRAP_TYPE_NONE:
+               fixup = s390_search_extables(regs->psw.addr);
+               if (fixup)
+                       regs->psw.addr = extable_fixup(fixup);
+               break;
+       case BUG_TRAP_TYPE_WARN:
+               break;
+       case BUG_TRAP_TYPE_BUG:
+               die(regs, "monitor event");
+               break;
+       }
+}
+
 void kernel_stack_overflow(struct pt_regs *regs)
 {
        bust_spinlocks(1);
@@ -255,8 +271,23 @@ void kernel_stack_overflow(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(kernel_stack_overflow);
 
+static void test_monitor_call(void)
+{
+       int val = 1;
+
+       asm volatile(
+               "       mc      0,0\n"
+               "0:     xgr     %0,%0\n"
+               "1:\n"
+               EX_TABLE(0b,1b)
+               : "+d" (val));
+       if (!val)
+               panic("Monitor call doesn't work!\n");
+}
+
 void __init trap_init(void)
 {
        sort_extable(__start_dma_ex_table, __stop_dma_ex_table);
        local_mcck_enable();
+       test_monitor_call();
 }