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| author | Vineet Gupta <vgupta@synopsys.com> | 2020-05-20 08:28:32 +0300 |
|---|---|---|
| committer | Vineet Gupta <vgupta@synopsys.com> | 2020-06-16 22:56:37 +0300 |
| commit | 00fdec98d9881bf5173af09aebd353ab3b9ac729 (patch) | |
| tree | 041616ad6c5cb039d0f236afdc32f965992689cf /arch/arc | |
| parent | b3a9e3b9622ae10064826dccb4f7a52bd88c7407 (diff) | |
| download | linux-00fdec98d9881bf5173af09aebd353ab3b9ac729.tar.xz | |
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>
Diffstat (limited to 'arch/arc')
| -rw-r--r-- | arch/arc/kernel/entry.S | 16 |
1 files changed, 5 insertions, 11 deletions
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S index 60406ec62eb8..ea00c8a17f07 100644 --- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -165,7 +165,6 @@ 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 @@ -208,15 +207,9 @@ 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 @@ -243,6 +236,10 @@ 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 @@ -250,9 +247,6 @@ 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 |