From: Vineet Gupta vgupta@synopsys.com
commit 00fdec98d9881bf5173af09aebd353ab3b9ac729 upstream.
Trap handler for syscall tracing reads EFA (Exception Fault Address), in case strace wants PC of trap instruction (EFA is not part of pt_regs as of current code).
However this EFA read is racy as it happens after dropping to pure kernel mode (re-enabling interrupts). A taken interrupt could context-switch, trigger a different task's trap, clobbering EFA for this execution context.
Fix this by reading EFA early, before re-enabling interrupts. A slight side benefit is de-duplication of FAKE_RET_FROM_EXCPN in trap handler. The trap handler is common to both ARCompact and ARCv2 builds too.
This just came out of code rework/review and no real problem was reported but is clearly a potential problem specially for strace.
Cc: stable@vger.kernel.org Signed-off-by: Vineet Gupta vgupta@synopsys.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arc/kernel/entry.S | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-)
--- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -156,7 +156,6 @@ END(EV_Extension) tracesys: ; save EFA in case tracer wants the PC of traced task ; using ERET won't work since next-PC has already committed - lr r12, [efa] GET_CURR_TASK_FIELD_PTR TASK_THREAD, r11 st r12, [r11, THREAD_FAULT_ADDR] ; thread.fault_address
@@ -199,15 +198,9 @@ tracesys_exit: ; Breakpoint TRAP ; --------------------------------------------- trap_with_param: - - ; stop_pc info by gdb needs this info - lr r0, [efa] + mov r0, r12 ; EFA in case ptracer/gdb wants stop_pc mov r1, sp
- ; Now that we have read EFA, it is safe to do "fake" rtie - ; and get out of CPU exception mode - FAKE_RET_FROM_EXCPN - ; Save callee regs in case gdb wants to have a look ; SP will grow up by size of CALLEE Reg-File ; NOTE: clobbers r12 @@ -234,6 +227,10 @@ ENTRY(EV_Trap)
EXCEPTION_PROLOGUE
+ lr r12, [efa] + + FAKE_RET_FROM_EXCPN + ;============ TRAP 1 :breakpoints ; Check ECR for trap with arg (PROLOGUE ensures r9 has ECR) bmsk.f 0, r9, 7 @@ -241,9 +238,6 @@ ENTRY(EV_Trap)
;============ TRAP (no param): syscall top level
- ; First return from Exception to pure K mode (Exception/IRQs renabled) - FAKE_RET_FROM_EXCPN - ; If syscall tracing ongoing, invoke pre-post-hooks GET_CURR_THR_INFO_FLAGS r10 btst r10, TIF_SYSCALL_TRACE