powerpc fixes for 4.4 #2

- tm: Block signal return from setting invalid MSR state from Michael Neuling
  - tm: Check for already reclaimed tasks from Michael Neuling
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Merge tag 'powerpc-4.4-3' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux

Pull powerpc fixes from Michael Ellerman:

 - tm: Block signal return from setting invalid MSR state from Michael
   Neuling

 - tm: Check for already reclaimed tasks from Michael Neuling

* tag 'powerpc-4.4-3' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  powerpc/tm: Check for already reclaimed tasks
  powerpc/tm: Block signal return setting invalid MSR state

arch/powerpc/include/asm/reg.h

@@ -108,6 +108,7 @@
 #define MSR_TS_T	__MASK(MSR_TS_T_LG)	/*  Transaction Transactional */
 #define MSR_TS_MASK	(MSR_TS_T | MSR_TS_S)   /* Transaction State bits */
 #define MSR_TM_ACTIVE(x) (((x) & MSR_TS_MASK) != 0) /* Transaction active? */
+#define MSR_TM_RESV(x) (((x) & MSR_TS_MASK) == MSR_TS_MASK) /* Reserved */
 #define MSR_TM_TRANSACTIONAL(x)	(((x) & MSR_TS_MASK) == MSR_TS_T)
 #define MSR_TM_SUSPENDED(x)	(((x) & MSR_TS_MASK) == MSR_TS_S)
 

arch/powerpc/kernel/process.c

@@ -551,6 +551,24 @@ static void tm_reclaim_thread(struct thread_struct *thr,
 		msr_diff &= MSR_FP | MSR_VEC | MSR_VSX | MSR_FE0 | MSR_FE1;
 	}
 
+	/*
+	 * Use the current MSR TM suspended bit to track if we have
+	 * checkpointed state outstanding.
+	 * On signal delivery, we'd normally reclaim the checkpointed
+	 * state to obtain stack pointer (see:get_tm_stackpointer()).
+	 * This will then directly return to userspace without going
+	 * through __switch_to(). However, if the stack frame is bad,
+	 * we need to exit this thread which calls __switch_to() which
+	 * will again attempt to reclaim the already saved tm state.
+	 * Hence we need to check that we've not already reclaimed
+	 * this state.
+	 * We do this using the current MSR, rather tracking it in
+	 * some specific thread_struct bit, as it has the additional
+	 * benifit of checking for a potential TM bad thing exception.
+	 */
+	if (!MSR_TM_SUSPENDED(mfmsr()))
+		return;
+
 	tm_reclaim(thr, thr->regs->msr, cause);
 
 	/* Having done the reclaim, we now have the checkpointed

arch/powerpc/kernel/signal_32.c

@@ -875,6 +875,15 @@ static long restore_tm_user_regs(struct pt_regs *regs,
 		return 1;
 #endif /* CONFIG_SPE */
 
+	/* Get the top half of the MSR from the user context */
+	if (__get_user(msr_hi, &tm_sr->mc_gregs[PT_MSR]))
+		return 1;
+	msr_hi <<= 32;
+	/* If TM bits are set to the reserved value, it's an invalid context */
+	if (MSR_TM_RESV(msr_hi))
+		return 1;
+	/* Pull in the MSR TM bits from the user context */
+	regs->msr = (regs->msr & ~MSR_TS_MASK) | (msr_hi & MSR_TS_MASK);
 	/* Now, recheckpoint.  This loads up all of the checkpointed (older)
 	 * registers, including FP and V[S]Rs.  After recheckpointing, the
 	 * transactional versions should be loaded.
@@ -884,11 +893,6 @@ static long restore_tm_user_regs(struct pt_regs *regs,
 	current->thread.tm_texasr |= TEXASR_FS;
 	/* This loads the checkpointed FP/VEC state, if used */
 	tm_recheckpoint(&current->thread, msr);
-	/* Get the top half of the MSR */
-	if (__get_user(msr_hi, &tm_sr->mc_gregs[PT_MSR]))
-		return 1;
-	/* Pull in MSR TM from user context */
-	regs->msr = (regs->msr & ~MSR_TS_MASK) | ((msr_hi<<32) & MSR_TS_MASK);
 
 	/* This loads the speculative FP/VEC state, if used */
 	if (msr & MSR_FP) {

arch/powerpc/kernel/signal_64.c

@@ -438,6 +438,10 @@ static long restore_tm_sigcontexts(struct pt_regs *regs,
 
 	/* get MSR separately, transfer the LE bit if doing signal return */
 	err |= __get_user(msr, &sc->gp_regs[PT_MSR]);
+	/* Don't allow reserved mode. */
+	if (MSR_TM_RESV(msr))
+		return -EINVAL;
+
 	/* pull in MSR TM from user context */
 	regs->msr = (regs->msr & ~MSR_TS_MASK) | (msr & MSR_TS_MASK);