ARCv2: STAR 9000808988: signals involving Delay Slot
Reported by Anton as LTP:munmap01 failing with Illegal Instruction
Exception.
--------------------->8--------------------------------------
mmap2(NULL, 24576, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x200d2000
munmap(0x200d2000, 24576) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x200d2000}
---
potentially unexpected fatal signal 4.
Path: /munmap01
CPU: 0 PID: 61 Comm: munmap01 Not tainted 3.13.0-g5d5c46d9a556 #8
task: 9f1a8000 ti: 9f154000 task.ti: 9f154000
[ECR ]: 0x00020100 => Illegal Insn
[EFA ]: 0x0001354c
[BLINK ]: 0x200515d4
[ERET ]: 0x1354c
@off 0x1354c in [/munmap01]
VMA: 0x00010000 to 0x00018000
[STAT32]: 0x800802c0
...
--------------------->8--------------------------------------
The issue was
1. munmap01 accessed unmapped memory (on purpose) with signal handler
installed for SIGSEGV
2. The faulting instruction happened to be in Delay Slot
00011864 <main>:
11908: bl.d 13284 <tst_resm>
1190c: stb r16,[r2]
3. kernel sets up the reg file for signal handler and correctly clears
the DE bit in pt_regs->status32 placeholder
4. However RESTORE_CALLEE_SAVED_USER macro is not adjusted for ARCv2,
and it over-writes the above with orig/stale value of status32
5. After RTIE, userspace signal handler executes a non branch
instruction with DE bit set, triggering Illegal Instruction Exception.
Reported-by: Anton Kolesov <akolesov@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
diff --git a/arch/arc/include/asm/entry.h b/arch/arc/include/asm/entry.h
index 29d0ab6..ad7860c 100644
--- a/arch/arc/include/asm/entry.h
+++ b/arch/arc/include/asm/entry.h
@@ -125,8 +125,6 @@
POP r13
.endm
-#define OFF_USER_R25_FROM_R24 (SZ_CALLEE_REGS + SZ_PT_REGS - 8)/4
-
/*--------------------------------------------------------------
* Collect User Mode callee regs as struct callee_regs - needed by
* fork/do_signal/unaligned-access-emulation.
@@ -139,12 +137,13 @@
*-------------------------------------------------------------*/
.macro SAVE_CALLEE_SAVED_USER
+ mov r12, sp ; save SP as ref to pt_regs
SAVE_R13_TO_R24
#ifdef CONFIG_ARC_CURR_IN_REG
- ; Retrieve orig r25 and save it on stack
- ld.as r12, [sp, OFF_USER_R25_FROM_R24]
- st.a r12, [sp, -4]
+ ; Retrieve orig r25 and save it with rest of callee_regs
+ ld.as r12, [r12, PT_user_r25]
+ PUSH r12
#else
PUSH r25
#endif
@@ -191,12 +190,16 @@
.macro RESTORE_CALLEE_SAVED_USER
#ifdef CONFIG_ARC_CURR_IN_REG
- ld.ab r12, [sp, 4]
- st.as r12, [sp, OFF_USER_R25_FROM_R24]
+ POP r12
#else
POP r25
#endif
RESTORE_R24_TO_R13
+
+ ; SP is back to start of pt_regs
+#ifdef CONFIG_ARC_CURR_IN_REG
+ st.as r12, [sp, PT_user_r25]
+#endif
.endm
/*--------------------------------------------------------------
diff --git a/arch/arc/kernel/asm-offsets.c b/arch/arc/kernel/asm-offsets.c
index b9cf233..605281f 100644
--- a/arch/arc/kernel/asm-offsets.c
+++ b/arch/arc/kernel/asm-offsets.c
@@ -60,5 +60,7 @@
DEFINE(SZ_CALLEE_REGS, sizeof(struct callee_regs));
DEFINE(SZ_PT_REGS, sizeof(struct pt_regs));
+ DEFINE(PT_user_r25, offsetof(struct pt_regs, user_r25));
+
return 0;
}