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tmp_suning_uos_patched/arch/arc/kernel/entry.S
Vineet Gupta 00fdec98d9 ARC: entry: fix potential EFA clobber when TIF_SYSCALL_TRACE 
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>
2020-06-16 12:56:37 -07:00

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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Common Low Level Interrupts/Traps/Exceptions(non-TLB) Handling for ARC
* (included from entry-<isa>.S
*
* Copyright (C) 2014-15 Synopsys, Inc. (www.synopsys.com)
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
*/
/*------------------------------------------------------------------
* Function ABI
*------------------------------------------------------------------
*
* Arguments r0 - r7
* Caller Saved Registers r0 - r12
* Callee Saved Registers r13- r25
* Global Pointer (gp) r26
* Frame Pointer (fp) r27
* Stack Pointer (sp) r28
* Branch link register (blink) r31
*------------------------------------------------------------------
*/
;################### Special Sys Call Wrappers ##########################
ENTRY(sys_clone_wrapper)
SAVE_CALLEE_SAVED_USER
bl @sys_clone
DISCARD_CALLEE_SAVED_USER
GET_CURR_THR_INFO_FLAGS r10
btst r10, TIF_SYSCALL_TRACE
bnz tracesys_exit
b .Lret_from_system_call
END(sys_clone_wrapper)
ENTRY(sys_clone3_wrapper)
SAVE_CALLEE_SAVED_USER
bl @sys_clone3
DISCARD_CALLEE_SAVED_USER
GET_CURR_THR_INFO_FLAGS r10
btst r10, TIF_SYSCALL_TRACE
bnz tracesys_exit
b .Lret_from_system_call
END(sys_clone3_wrapper)
ENTRY(ret_from_fork)
; when the forked child comes here from the __switch_to function
; r0 has the last task pointer.
; put last task in scheduler queue
jl @schedule_tail
ld r9, [sp, PT_status32]
brne r9, 0, 1f
jl.d [r14] ; kernel thread entry point
mov r0, r13 ; (see PF_KTHREAD block in copy_thread)
1:
; Return to user space
; 1. Any forked task (Reach here via BRne above)
; 2. First ever init task (Reach here via return from JL above)
; This is the historic "kernel_execve" use-case, to return to init
; user mode, in a round about way since that is always done from
; a kernel thread which is executed via JL above but always returns
; out whenever kernel_execve (now inline do_fork()) is involved
b ret_from_exception
END(ret_from_fork)
;################### Non TLB Exception Handling #############################
; ---------------------------------------------
; Instruction Error Exception Handler
; ---------------------------------------------
ENTRY(instr_service)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN
bl do_insterror_or_kprobe
b ret_from_exception
END(instr_service)
; ---------------------------------------------
; Machine Check Exception Handler
; ---------------------------------------------
ENTRY(EV_MachineCheck)
EXCEPTION_PROLOGUE
lr r2, [ecr]
lr r0, [efa]
mov r1, sp
; hardware auto-disables MMU, re-enable it to allow kernel vaddr
; access for say stack unwinding of modules for crash dumps
lr r3, [ARC_REG_PID]
or r3, r3, MMU_ENABLE
sr r3, [ARC_REG_PID]
lsr r3, r2, 8
bmsk r3, r3, 7
brne r3, ECR_C_MCHK_DUP_TLB, 1f
bl do_tlb_overlap_fault
b ret_from_exception
1:
; DEAD END: can't do much, display Regs and HALT
SAVE_CALLEE_SAVED_USER
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
j do_machine_check_fault
END(EV_MachineCheck)
; ---------------------------------------------
; Privilege Violation Exception Handler
; ---------------------------------------------
ENTRY(EV_PrivilegeV)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN
bl do_privilege_fault
b ret_from_exception
END(EV_PrivilegeV)
; ---------------------------------------------
; Extension Instruction Exception Handler
; ---------------------------------------------
ENTRY(EV_Extension)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN
bl do_extension_fault
b ret_from_exception
END(EV_Extension)
;################ Trap Handling (Syscall, Breakpoint) ##################
; ---------------------------------------------
; syscall Tracing
; ---------------------------------------------
tracesys:
; save EFA in case tracer wants the PC of traced task
; using ERET won't work since next-PC has already committed
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r11
st r12, [r11, THREAD_FAULT_ADDR] ; thread.fault_address
; PRE Sys Call Ptrace hook
mov r0, sp ; pt_regs needed
bl @syscall_trace_entry
; Tracing code now returns the syscall num (orig or modif)
mov r8, r0
; Do the Sys Call as we normally would.
; Validate the Sys Call number
cmp r8, NR_syscalls
mov.hi r0, -ENOSYS
bhi tracesys_exit
; Restore the sys-call args. Mere invocation of the hook abv could have
; clobbered them (since they are in scratch regs). The tracer could also
; have deliberately changed the syscall args: r0-r7
ld r0, [sp, PT_r0]
ld r1, [sp, PT_r1]
ld r2, [sp, PT_r2]
ld r3, [sp, PT_r3]
ld r4, [sp, PT_r4]
ld r5, [sp, PT_r5]
ld r6, [sp, PT_r6]
ld r7, [sp, PT_r7]
ld.as r9, [sys_call_table, r8]
jl [r9] ; Entry into Sys Call Handler
tracesys_exit:
st r0, [sp, PT_r0] ; sys call return value in pt_regs
;POST Sys Call Ptrace Hook
bl @syscall_trace_exit
b ret_from_exception ; NOT ret_from_system_call at is saves r0 which
; we'd done before calling post hook above
; ---------------------------------------------
; Breakpoint TRAP
; ---------------------------------------------
trap_with_param:
mov r0, r12 ; EFA in case ptracer/gdb wants stop_pc
mov r1, sp
; Save callee regs in case gdb wants to have a look
; SP will grow up by size of CALLEE Reg-File
; NOTE: clobbers r12
SAVE_CALLEE_SAVED_USER
; save location of saved Callee Regs @ thread_struct->pc
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
; Call the trap handler
bl do_non_swi_trap
; unwind stack to discard Callee saved Regs
DISCARD_CALLEE_SAVED_USER
b ret_from_exception
; ---------------------------------------------
; syscall TRAP
; ABI: (r0-r7) upto 8 args, (r8) syscall number
; ---------------------------------------------
ENTRY(EV_Trap)
EXCEPTION_PROLOGUE
lr r12, [efa]
FAKE_RET_FROM_EXCPN
;============ TRAP 1 :breakpoints
; Check ECR for trap with arg (PROLOGUE ensures r10 has ECR)
bmsk.f 0, r10, 7
bnz trap_with_param
;============ TRAP (no param): syscall top level
; If syscall tracing ongoing, invoke pre-post-hooks
GET_CURR_THR_INFO_FLAGS r10
btst r10, TIF_SYSCALL_TRACE
bnz tracesys ; this never comes back
;============ Normal syscall case
; syscall num shd not exceed the total system calls avail
cmp r8, NR_syscalls
mov.hi r0, -ENOSYS
bhi .Lret_from_system_call
; Offset into the syscall_table and call handler
ld.as r9,[sys_call_table, r8]
jl [r9] ; Entry into Sys Call Handler
.Lret_from_system_call:
st r0, [sp, PT_r0] ; sys call return value in pt_regs
; fall through to ret_from_exception
END(EV_Trap)
;############# Return from Intr/Excp/Trap (Linux Specifics) ##############
;
; If ret to user mode do we need to handle signals, schedule() et al.
ENTRY(ret_from_exception)
; Pre-{IRQ,Trap,Exception} K/U mode from pt_regs->status32
ld r8, [sp, PT_status32] ; returning to User/Kernel Mode
bbit0 r8, STATUS_U_BIT, resume_kernel_mode
; Before returning to User mode check-for-and-complete any pending work
; such as rescheduling/signal-delivery etc.
resume_user_mode_begin:
; Disable IRQs to ensures that chk for pending work itself is atomic
; (and we don't end up missing a NEED_RESCHED/SIGPENDING due to an
; interim IRQ).
IRQ_DISABLE r10
; Fast Path return to user mode if no pending work
GET_CURR_THR_INFO_FLAGS r9
and.f 0, r9, _TIF_WORK_MASK
bz .Lrestore_regs
; --- (Slow Path #1) task preemption ---
bbit0 r9, TIF_NEED_RESCHED, .Lchk_pend_signals
mov blink, resume_user_mode_begin ; tail-call to U mode ret chks
j @schedule ; BTST+Bnz causes relo error in link
.Lchk_pend_signals:
IRQ_ENABLE r10
; --- (Slow Path #2) pending signal ---
mov r0, sp ; pt_regs for arg to do_signal()/do_notify_resume()
GET_CURR_THR_INFO_FLAGS r9
bbit0 r9, TIF_SIGPENDING, .Lchk_notify_resume
; Normal Trap/IRQ entry only saves Scratch (caller-saved) regs
; in pt_reg since the "C" ABI (kernel code) will automatically
; save/restore callee-saved regs.
;
; However, here we need to explicitly save callee regs because
; (i) If this signal causes coredump - full regfile needed
; (ii) If signal is SIGTRAP/SIGSTOP, task is being traced thus
; tracer might call PEEKUSR(CALLEE reg)
;
; NOTE: SP will grow up by size of CALLEE Reg-File
SAVE_CALLEE_SAVED_USER ; clobbers r12
; save location of saved Callee Regs @ thread_struct->callee
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
bl @do_signal
; Ideally we want to discard the Callee reg above, however if this was
; a tracing signal, tracer could have done a POKEUSR(CALLEE reg)
RESTORE_CALLEE_SAVED_USER
b resume_user_mode_begin ; loop back to start of U mode ret
; --- (Slow Path #3) notify_resume ---
.Lchk_notify_resume:
btst r9, TIF_NOTIFY_RESUME
blnz @do_notify_resume
b resume_user_mode_begin ; unconditionally back to U mode ret chks
; for single exit point from this block
resume_kernel_mode:
; Disable Interrupts from this point on
; CONFIG_PREEMPTION: This is a must for preempt_schedule_irq()
; !CONFIG_PREEMPTION: To ensure restore_regs is intr safe
IRQ_DISABLE r9
#ifdef CONFIG_PREEMPTION
; Can't preempt if preemption disabled
GET_CURR_THR_INFO_FROM_SP r10
ld r8, [r10, THREAD_INFO_PREEMPT_COUNT]
brne r8, 0, .Lrestore_regs
; check if this task's NEED_RESCHED flag set
ld r9, [r10, THREAD_INFO_FLAGS]
bbit0 r9, TIF_NEED_RESCHED, .Lrestore_regs
; Invoke PREEMPTION
jl preempt_schedule_irq
; preempt_schedule_irq() always returns with IRQ disabled
#endif
b .Lrestore_regs
##### DONT ADD CODE HERE - .Lrestore_regs actually follows in entry-<isa>.S
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