[PATCH v2 0/2] powerpc/tm: Fixes for crashes

[PATCH v2 0/2] powerpc/tm: Fixes for crashes

[Michael Neuling]

Here's a couple of fixes for crashes with the TM signals code.

v2:
 - Split fixes to go into stable from other patches
   - other patches will be sent separately
 - Updates based on mpe's review:
   - add correct linux version for stable tag
   - fix white space issues
   - cleanup signal_32 changes to make code easier to read
   - remove signal 64 setting local variable just before return.

Michael Neuling (2):
  powerpc/tm: Block signal return setting invalid MSR state
  powerpc/tm: Check for already reclaimed tasks

 arch/powerpc/include/asm/reg.h  |  1 +
 arch/powerpc/kernel/process.c   | 18 ++++++++++++++++++
 arch/powerpc/kernel/signal_32.c | 15 +++++++++------
 arch/powerpc/kernel/signal_64.c |  4 ++++
 4 files changed, 32 insertions(+), 6 deletions(-)

-- 
2.5.0

[PATCH v2 1/2] powerpc/tm: Block signal return setting invalid MSR state

[Michael Neuling]

Currently we allow both the MSR T and S bits to be set by userspace on
a signal return.  Unfortunately this is a reserved configuration and
will cause a TM Bad Thing exception if attempted (via rfid).

This patch checks for this case in both the 32 and 64 bit signals
code.  If both T and S are set, we mark the context as invalid.

Found using a syscall fuzzer.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: stable@vger.kernel.org # v3.9+
---
 arch/powerpc/include/asm/reg.h  |  1 +
 arch/powerpc/kernel/signal_32.c | 14 +++++++++-----
 arch/powerpc/kernel/signal_64.c |  4 ++++
 3 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h
index a908ada..2220f7a 100644
--- a/arch/powerpc/include/asm/reg.h
+++ b/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)
 
diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 0dbee46..ef7c24e 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/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) {
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c
index 20756df..c676ece 100644
--- a/arch/powerpc/kernel/signal_64.c
+++ b/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);
 
-- 
2.5.0

Re: [v2, 1/2] powerpc/tm: Block signal return setting invalid MSR state

[Michael Ellerman]

On Thu, 2015-19-11 at 04:44:44 UTC, Michael Neuling wrote:
> Currently we allow both the MSR T and S bits to be set by userspace on
> a signal return.  Unfortunately this is a reserved configuration and
> will cause a TM Bad Thing exception if attempted (via rfid).

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/d2b9d2a5ad5ef04ff978c992

cheers

[PATCH v2 2/2] powerpc/tm: Check for already reclaimed tasks

[Michael Neuling]

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.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: stable@vger.kernel.org # v3.9+
---
 arch/powerpc/kernel/process.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 75b6676..646bf4d 100644
--- a/arch/powerpc/kernel/process.c
+++ b/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
-- 
2.5.0

Re: [v2,2/2] powerpc/tm: Check for already reclaimed tasks

[Michael Ellerman]

On Thu, 2015-19-11 at 04:44:45 UTC, Michael Neuling wrote:
> 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.

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/7f821fc9c77a9b01fe7b1d6e

cheers