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Subject[PATCH 5.5 321/399] s390: fix __EMIT_BUG() macro
Date
From: Sven Schnelle <svens@linux.ibm.com>

[ Upstream commit 17248ea0367465f4aaef728f6af661ed38e38cf1 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/boot/head.S | 2 +-
arch/s390/include/asm/bug.h | 16 ++++++--------
arch/s390/kernel/entry.h | 1 +
arch/s390/kernel/pgm_check.S | 2 +-
arch/s390/kernel/traps.c | 41 +++++++++++++++++++++++++++++++-----
5 files changed, 46 insertions(+), 16 deletions(-)

diff --git a/arch/s390/boot/head.S b/arch/s390/boot/head.S
index 4b86a8d3c1219..dae10961d0724 100644
--- 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 a2b11ac00f607..7725f8006fdfb 100644
--- 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 b2956d49b6ad7..1d3927e01a5fd 100644
--- 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 59dee9d3bebf1..eee3a482195a6 100644
--- 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 164c0282b41ae..dc75588d78943 100644
--- 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();
}
--
2.20.1


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