Skip to content

Commit 7f821fc

Browse files
mikeympe
authored andcommitted
powerpc/tm: Check for already reclaimed tasks
Currently we can hit a scenario where we'll tm_reclaim() twice. This results in a TM bad thing exception because the second reclaim occurs when not in suspend mode. The scenario in which this can happen is the following. We attempt to deliver a signal to userspace. To do this we need obtain the stack pointer to write the signal context. To get this stack pointer we must tm_reclaim() in case we need to use the checkpointed stack pointer (see get_tm_stackpointer()). Normally we'd then return directly to userspace to deliver the signal without going through __switch_to(). Unfortunatley, if at this point we get an error (such as a bad userspace stack pointer), we need to exit the process. The exit will result in a __switch_to(). __switch_to() will attempt to save the process state which results in another tm_reclaim(). This tm_reclaim() now causes a TM Bad Thing exception as this state has already been saved and the processor is no longer in TM suspend mode. Whee! This patch checks the state of the MSR to ensure we are TM suspended before we attempt the tm_reclaim(). If we've already saved the state away, we should no longer be in TM suspend mode. This has the additional advantage of checking for a potential TM Bad Thing exception. Found using syscall fuzzer. Fixes: fb09692 ("powerpc: Add reclaim and recheckpoint functions for context switching transactional memory processes") Cc: stable@vger.kernel.org # v3.9+ Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
1 parent d2b9d2a commit 7f821fc

File tree

1 file changed

+18
-0
lines changed

1 file changed

+18
-0
lines changed

Diff for: arch/powerpc/kernel/process.c

+18
Original file line numberDiff line numberDiff line change
@@ -551,6 +551,24 @@ static void tm_reclaim_thread(struct thread_struct *thr,
551551
msr_diff &= MSR_FP | MSR_VEC | MSR_VSX | MSR_FE0 | MSR_FE1;
552552
}
553553

554+
/*
555+
* Use the current MSR TM suspended bit to track if we have
556+
* checkpointed state outstanding.
557+
* On signal delivery, we'd normally reclaim the checkpointed
558+
* state to obtain stack pointer (see:get_tm_stackpointer()).
559+
* This will then directly return to userspace without going
560+
* through __switch_to(). However, if the stack frame is bad,
561+
* we need to exit this thread which calls __switch_to() which
562+
* will again attempt to reclaim the already saved tm state.
563+
* Hence we need to check that we've not already reclaimed
564+
* this state.
565+
* We do this using the current MSR, rather tracking it in
566+
* some specific thread_struct bit, as it has the additional
567+
* benifit of checking for a potential TM bad thing exception.
568+
*/
569+
if (!MSR_TM_SUSPENDED(mfmsr()))
570+
return;
571+
554572
tm_reclaim(thr, thr->regs->msr, cause);
555573

556574
/* Having done the reclaim, we now have the checkpointed

0 commit comments

Comments
 (0)