From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-x242.google.com (mail-pa0-x242.google.com [IPv6:2607:f8b0:400e:c03::242]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3sHlj128lxzDrJq for ; Mon, 22 Aug 2016 17:35:17 +1000 (AEST) Received: by mail-pa0-x242.google.com with SMTP id cf3so7560918pad.2 for ; Mon, 22 Aug 2016 00:35:17 -0700 (PDT) Message-ID: <1471851310.31624.1.camel@gmail.com> Subject: Re: [PATCH] powerpc: signals: Discard transaction state from signal frames From: Cyril Bur To: linuxppc-dev@lists.ozlabs.org, benh@kernel.crashing.org Cc: mikey@neuling.org, Laurent Dufour , Simon Guo Date: Mon, 22 Aug 2016 17:35:10 +1000 In-Reply-To: <20160822073206.1342-1-cyrilbur@gmail.com> References: <20160822073206.1342-1-cyrilbur@gmail.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 2016-08-22 at 17:32 +1000, Cyril Bur wrote: The subject prefix should have contained V2. Sorry. > Userspace can begin and suspend a transaction within the signal > handler which means they might enter sys_rt_sigreturn() with the > processor in suspended state. > > sys_rt_sigreturn() wants to restore process context (which may have > been in a transaction before signal delivery). To do this it must > restore TM SPRS. To achieve this, any transaction initiated within > the > signal frame must be discarded in order to be able to restore TM SPRs > as TM SPRs can only be manipulated non-transactionally.. > From the PowerPC ISA: >   TM Bad Thing Exception [Category: Transactional Memory] >    An attempt is made to execute a mtspr targeting a TM register in >    other than Non-transactional state. > > Not doing so results in a TM Bad Thing: > [12045.221359] Kernel BUG at c000000000050a40 [verbose debug info > unavailable] > [12045.221470] Unexpected TM Bad Thing exception at c000000000050a40 > (msr 0x201033) > [12045.221540] Oops: Unrecoverable exception, sig: 6 [#1] > [12045.221586] SMP NR_CPUS=2048 NUMA PowerNV > [12045.221634] Modules linked in: xt_CHECKSUM iptable_mangle > ipt_MASQUERADE >  nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat > nf_conntrack_ipv4 nf_defrag_ipv4 >  xt_conntrack nf_conntrack ipt_REJECT nf_reject_ipv4 xt_tcpudp bridge > stp llc ebtable_filter >  ebtables ip6table_filter ip6_tables iptable_filter ip_tables > x_tables kvm_hv kvm >  uio_pdrv_genirq ipmi_powernv uio powernv_rng ipmi_msghandler autofs4 > ses enclosure >  scsi_transport_sas bnx2x ipr mdio libcrc32c > [12045.222167] CPU: 68 PID: 6178 Comm: sigreturnpanic Not tainted > 4.7.0 #34 > [12045.222224] task: c0000000fce38600 ti: c0000000fceb4000 task.ti: > c0000000fceb4000 > [12045.222293] NIP: c000000000050a40 LR: c0000000000163bc CTR: > 0000000000000000 > [12045.222361] REGS: c0000000fceb7ac0 TRAP: 0700   Not tainted > (4.7.0) > [12045.222418] MSR: 9000000300201033 > CR: 28444280  XER: 20000000 > [12045.222625] CFAR: c0000000000163b8 SOFTE: 0 PACATMSCRATCH: > 900000014280f033 > GPR00: 01100000b8000001 c0000000fceb7d40 c00000000139c100 > c0000000fce390d0 > GPR04: 900000034280f033 0000000000000000 0000000000000000 > 0000000000000000 > GPR08: 0000000000000000 b000000000001033 0000000000000001 > 0000000000000000 > GPR12: 0000000000000000 c000000002926400 0000000000000000 > 0000000000000000 > GPR16: 0000000000000000 0000000000000000 0000000000000000 > 0000000000000000 > GPR20: 0000000000000000 0000000000000000 0000000000000000 > 0000000000000000 > GPR24: 0000000000000000 00003ffff98cadd0 00003ffff98cb470 > 0000000000000000 > GPR28: 900000034280f033 c0000000fceb7ea0 0000000000000001 > c0000000fce390d0 > [12045.223535] NIP [c000000000050a40] tm_restore_sprs+0xc/0x1c > [12045.223584] LR [c0000000000163bc] tm_recheckpoint+0x5c/0xa0 > [12045.223630] Call Trace: > [12045.223655] [c0000000fceb7d80] [c000000000026e74] > sys_rt_sigreturn+0x494/0x6c0 > [12045.223738] [c0000000fceb7e30] [c0000000000092e0] > system_call+0x38/0x108 > [12045.223806] Instruction dump: > [12045.223841] 7c800164 4e800020 7c0022a6 f80304a8 7c0222a6 f80304b0 > 7c0122a6 f80304b8 > [12045.223955] 4e800020 e80304a8 7c0023a6 e80304b0 <7c0223a6> > e80304b8 7c0123a6 4e800020 > [12045.224074] ---[ end trace cb8002ee240bae76 ]--- > > It isn't clear exactly if there is really a use case for userspace > returning with a suspended transaction, however, doing so doesn't (on > its own) constitute a bad frame. As such, this patch simply discards > the transactional state of the context calling the sigreturn and > continues. > > Reported-by: Laurent Dufour > Signed-off-by: Cyril Bur > --- > V2: Move the code down into the #ifdef CONFIG_PPC_TRANSACTIONAL_MEM > (32 and 64 bit) > Add a small amount of text to Documentation > Adjust the commit message for clarity  > >  Documentation/powerpc/transactional_memory.txt |  2 ++ >  arch/powerpc/kernel/signal_32.c                | 12 ++++++++++++ >  arch/powerpc/kernel/signal_64.c                | 12 ++++++++++++ >  3 files changed, 26 insertions(+) > > diff --git a/Documentation/powerpc/transactional_memory.txt > b/Documentation/powerpc/transactional_memory.txt > index ba0a2a4..e32fdbb 100644 > --- a/Documentation/powerpc/transactional_memory.txt > +++ b/Documentation/powerpc/transactional_memory.txt > @@ -167,6 +167,8 @@ signal will be rolled back anyway. >  For signals taken in non-TM or suspended mode, we use the >  normal/non-checkpointed stack pointer. >   > +Any transaction initiated inside a sighandler and suspended on > return > +from the sighandler to the kernel will get reclaimed and discarded. >   >  Failure cause codes used by kernel >  ================================== > diff --git a/arch/powerpc/kernel/signal_32.c > b/arch/powerpc/kernel/signal_32.c > index b6aa378..31e4e15 100644 > --- a/arch/powerpc/kernel/signal_32.c > +++ b/arch/powerpc/kernel/signal_32.c > @@ -1226,7 +1226,19 @@ long sys_rt_sigreturn(int r3, int r4, int r5, > int r6, int r7, int r8, >   (regs->gpr[1] + __SIGNAL_FRAMESIZE + 16); >   if (!access_ok(VERIFY_READ, rt_sf, sizeof(*rt_sf))) >   goto bad; > + >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM > + /* > +  * If there is a transactional/suspended state then throw it > away. > +  * The purpose of a sigreturn is to destroy all traces of > the > +  * signal frame, this includes any transactional state > created > +  * within in. > +  * The cause is not important as there will never be a > +  * recheckpoint so it's not user visible. > +  */ > + if (MSR_TM_ACTIVE(mfmsr())) > + tm_reclaim_current(0); > + >   if (__get_user(tmp, &rt_sf->uc.uc_link)) >   goto bad; >   uc_transact = (struct ucontext __user *)(uintptr_t)tmp; > diff --git a/arch/powerpc/kernel/signal_64.c > b/arch/powerpc/kernel/signal_64.c > index 7e49984..8425eee 100644 > --- a/arch/powerpc/kernel/signal_64.c > +++ b/arch/powerpc/kernel/signal_64.c > @@ -676,7 +676,19 @@ int sys_rt_sigreturn(unsigned long r3, unsigned > long r4, unsigned long r5, >   if (__copy_from_user(&set, &uc->uc_sigmask, sizeof(set))) >   goto badframe; >   set_current_blocked(&set); > + >  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM > + /* > +  * If there is a transactional/suspended state then throw it > away. > +  * The purpose of a sigreturn is to destroy all traces of > the > +  * signal frame, this includes any transactional state > created > +  * within in. > +  * The cause is not important as there will never be a > +  * recheckpoint so it's not user visible. > +  */ > + if (MSR_TM_ACTIVE(mfmsr())) > + tm_reclaim_current(0); > + >   if (__get_user(msr, &uc->uc_mcontext.gp_regs[PT_MSR])) >   goto badframe; >   if (MSR_TM_ACTIVE(msr)) {