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| author | Vineet Gupta <vgupta@synopsys.com> | 2020-05-19 22:28:32 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-07-16 08:16:46 +0200 |
| commit | 854827a2697a9e538fbe9b7f68ee9405d18bcc53 (patch) | |
| tree | 7673463cf290bad35a694a299035f5618d227d51 /arch/arc/kernel | |
| parent | 37634f502b53f97dd7f6e4423881634a9f8b189f (diff) | |
| download | linux-stable-854827a2697a9e538fbe9b7f68ee9405d18bcc53.tar.gz linux-stable-854827a2697a9e538fbe9b7f68ee9405d18bcc53.tar.bz2 linux-stable-854827a2697a9e538fbe9b7f68ee9405d18bcc53.zip | |
ARC: entry: fix potential EFA clobber when TIF_SYSCALL_TRACE
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>
Diffstat (limited to 'arch/arc/kernel')
| -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 72be01270e24..ea74a1eee5d9 100644 --- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -153,7 +153,6 @@ 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 @@ -196,15 +195,9 @@ 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 @@ -231,6 +224,10 @@ 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 @@ -238,9 +235,6 @@ 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 |