[PATCH 3.14 46/59] powerpc/tm: Block signal return setting invalid MSR state

Greg Kroah-Hartman
2016-01-27T19:21:59Z

From: Michael Neuling <mikey@neuling.org>

commit d2b9d2a5ad5ef04ff978c9923d19730cb05efd55 upstream.

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.

Fixes: 2b0a576d15e0 ("powerpc: Add new transactional memory state to the signal context")
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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(-)

--- 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)

--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c
@@ -876,6 +876,15 @@ static long restore_tm_user_regs(struct
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.
@@ -885,11 +894,6 @@ static long restore_tm_user_regs(struct
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) {
--- a/arch/powerpc/kernel/signal_64.c
+++ b/arch/powerpc/kernel/signal_64.c
@@ -428,6 +428,10 @@ static long restore_tm_sigcontexts(struc

/* 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);