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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>
This commit is contained in:
Sven Schnelle 2020-01-15 13:42:27 +01:00 committed by Vasily Gorbik
parent 45f7a0da60
commit 17248ea036
5 changed files with 46 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/s390/boot/head.S
View File

@ -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

16
arch/s390/include/asm/bug.h
View File

@ -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))); \

1
arch/s390/kernel/entry.h
View File

@ -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);

2
arch/s390/kernel/pgm_check.S
View File

@ -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 */

41
arch/s390/kernel/traps.c
View File

@ -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();
}