From d2b9d2a5ad5ef04ff978c9923d19730cb05efd55 Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Thu, 19 Nov 2015 15:44:44 +1100 Subject: powerpc/tm: Block signal return setting invalid MSR state 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") Cc: stable@vger.kernel.org # v3.9+ Signed-off-by: Michael Neuling Signed-off-by: Michael Ellerman 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(¤t->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); -- cgit v0.10.2 From 7f821fc9c77a9b01fe7b1d6e72717b33d8d64142 Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Thu, 19 Nov 2015 15:44:45 +1100 Subject: 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: fb09692e71f1 ("powerpc: Add reclaim and recheckpoint functions for context switching transactional memory processes") Cc: stable@vger.kernel.org # v3.9+ Signed-off-by: Michael Neuling Signed-off-by: Michael Ellerman 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 -- cgit v0.10.2