On Mon, 2020-03-23 at 10:06 +1000, Nicholas Piggin wrote: > Haren Myneni's on March 18, 2020 5:27 am: > > On Tue, 2020-03-17 at 16:28 +1100, Michael Ellerman wrote: > >> Haren Myneni <ha...@linux.ibm.com> writes: > >> > For each fault CRB, update fault address in CRB (fault_storage_addr) > >> > and translation error status in CSB so that user space can touch the > >> > fault address and resend the request. If the user space passed invalid > >> > CSB address send signal to process with SIGSEGV. > >> > > >> > Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com> > >> > Signed-off-by: Haren Myneni <ha...@linux.ibm.com> > >> > --- > >> > arch/powerpc/platforms/powernv/vas-fault.c | 114 > >> > +++++++++++++++++++++++++++++ > >> > 1 file changed, 114 insertions(+) > >> > > >> > diff --git a/arch/powerpc/platforms/powernv/vas-fault.c > >> > b/arch/powerpc/platforms/powernv/vas-fault.c > >> > index 1c6d5cc..751ce48 100644 > >> > --- a/arch/powerpc/platforms/powernv/vas-fault.c > >> > +++ b/arch/powerpc/platforms/powernv/vas-fault.c > >> > @@ -11,6 +11,7 @@ > >> > #include <linux/slab.h> > >> > #include <linux/uaccess.h> > >> > #include <linux/kthread.h> > >> > +#include <linux/sched/signal.h> > >> > #include <linux/mmu_context.h> > >> > #include <asm/icswx.h> > >> > > >> > @@ -26,6 +27,118 @@ > >> > #define VAS_FAULT_WIN_FIFO_SIZE (4 << 20) > >> > > >> > /* > >> > + * Update the CSB to indicate a translation error. > >> > + * > >> > + * If we are unable to update the CSB means copy_to_user failed due to > >> > + * invalid csb_addr, send a signal to the process. > >> > + * > >> > + * Remaining settings in the CSB are based on wait_for_csb() of > >> > + * NX-GZIP. > >> > + */ > >> > +static void update_csb(struct vas_window *window, > >> > + struct coprocessor_request_block *crb) > >> > +{ > >> > + int rc; > >> > + struct pid *pid; > >> > + void __user *csb_addr; > >> > + struct task_struct *tsk; > >> > + struct kernel_siginfo info; > >> > + struct coprocessor_status_block csb; > >> > >> csb is on the stack, and later copied to user, which is a risk for > >> creating an infoleak. > >> > >> Also please use reverse Christmas tree layout for your variables. > >> > >> > + > >> > + /* > >> > + * NX user space windows can not be opened for task->mm=NULL > >> > + * and faults will not be generated for kernel requests. > >> > + */ > >> > + if (!window->mm || !window->user_win) > >> > + return; > >> > >> If that's a should-never-happen condition then should it do a > >> WARN_ON_ONCE() rather than silently returning? > > > > Will add WARN_ON > > > >> > >> > + csb_addr = (void __user *)be64_to_cpu(crb->csb_addr); > >> > + > >> > + csb.cc = CSB_CC_TRANSLATION; > >> > + csb.ce = CSB_CE_TERMINATION; > >> > + csb.cs = 0; > >> > + csb.count = 0; > >> > + > >> > + /* > >> > + * NX operates and returns in BE format as defined CRB struct. > >> > + * So return fault_storage_addr in BE as NX pastes in FIFO and > >> > + * expects user space to convert to CPU format. > >> > + */ > >> > + csb.address = crb->stamp.nx.fault_storage_addr; > >> > + csb.flags = 0; > >> > >> I'm pretty sure this has initialised all the fields of csb. > >> > >> But, I'd still be much happier if you zeroed the whole struct to begin > >> with, that way we know for sure we can't leak any uninitialised bytes to > >> userspace. It's only 16 bytes so it shouldn't add any noticeable > >> overhead. > > Sure, will initialize csb > >> > >> > + > >> > + pid = window->pid; > >> > + tsk = get_pid_task(pid, PIDTYPE_PID); > >> > + /* > >> > + * Send window will be closed after processing all NX requests > >> > + * and process exits after closing all windows. In multi-thread > >> > + * applications, thread may not exists, but does not close FD > >> > + * (means send window) upon exit. Parent thread (tgid) can use > >> > + * and close the window later. > >> > + * pid and mm references are taken when window is opened by > >> > + * process (pid). So tgid is used only when child thread opens > >> > + * a window and exits without closing it in multithread tasks. > >> > + */ > >> > + if (!tsk) { > >> > + pid = window->tgid; > >> > + tsk = get_pid_task(pid, PIDTYPE_PID); > >> > + /* > >> > + * Parent thread will be closing window during its exit. > >> > + * So should not get here. > >> > + */ > >> > + if (!tsk) > >> > + return; > >> > >> Similar question on WARN_ON_ONCE() > > Yes, we can add WARN_ON > >> > >> > + } > >> > + > >> > + /* Return if the task is exiting. */ > >> > >> Why? Just because it's no use? It's racy isn't it, so it can't be for > >> correctness? > > Yes process is exiting and no need to update CSB. We release the > > task->usage refcount after copy_to_user(). > > > >> > >> > + if (tsk->flags & PF_EXITING) { > >> > + put_task_struct(tsk); > >> > + return; > >> > + } > >> > + > >> > + use_mm(window->mm); > >> > >> There's no check that csb_addr is actually pointing into userspace, but > >> copy_to_user() does it for you. > >> > >> > + rc = copy_to_user(csb_addr, &csb, sizeof(csb)); > >> > + /* > >> > + * User space polls on csb.flags (first byte). So add barrier > >> > + * then copy first byte with csb flags update. > >> > + */ > >> > + smp_mb(); > >> > >> You only need to order the stores above vs the store below to csb.flags. > >> So you should only need an smp_wmb() here. > > Sure, will add > > if (!rc) { > > csb.flags = CSB_V; > > smp_mb(); > > rc = copy_to_user(csb_addr, &csb, sizeof(u8)); > > } > > > >> > >> > + if (!rc) { > >> > + csb.flags = CSB_V; > >> > + rc = copy_to_user(csb_addr, &csb, sizeof(u8)); > >> > + } > >> > + unuse_mm(window->mm); > >> > + put_task_struct(tsk); > >> > + > >> > + /* Success */ > >> > + if (!rc) > >> > + return; > >> > + > >> > + pr_debug("Invalid CSB address 0x%p signalling pid(%d)\n", > >> > + csb_addr, pid_vnr(pid)); > >> > + > >> > + clear_siginfo(&info); > >> > + info.si_signo = SIGSEGV; > >> > + info.si_errno = EFAULT; > >> > + info.si_code = SEGV_MAPERR; > >> > + info.si_addr = csb_addr; > >> > + > >> > + /* > >> > + * process will be polling on csb.flags after request is sent to > >> > + * NX. So generally CSB update should not fail except when an > >> > + * application does not follow the process properly. So an error > >> > + * message will be displayed and leave it to user space whether > >> > + * to ignore or handle this signal. > >> > + */ > > The code would read a bit better if this comment goes at the start of > this error handling process it describes (before the error message). > > And I feel a bit hypocritical complaining about readability, but it > could possibly do with some work. > > /* > * The application should have provided a valid mapping for the > * csb, and not unmap it before the csb.flags update, so the > * copy_to_user should not fail. > * > * If the application fails to follow this protocol, log a kernel > * error and send a SEGV to the pid. This signal may be ignored, > * so can't use force_sig_fault_to_task() > */ > > Something like tthat?
Thanks Nick, will update. > > >> > + rcu_read_lock(); > >> > + rc = kill_pid_info(SIGSEGV, &info, pid); > >> > + rcu_read_unlock(); > > ipc/mqueue.c says kill_pid_info doesn't need rcu_read_lock(). AFAIKS > it's held around kill_pid_info in kernel/signal.c for the find_vpid(). I was following as in kill_proc_info(). Will remove rcu_read_lock(). > > Thanks, > Nick > > >> > >> Shouldn't this be using force_sig_fault_to_task() or another helper, > >> rather than open-coding? > > > > Applications or nxz library can ignore this signal based on si_addr or > > take action like resend new request with valid csb_addr. Hence I did not > > use force_sig_info_to_task(). > > > > >> > >> > + > >> > + pr_devel("%s(): pid %d kill_proc_info() rc %d\n", __func__, > >> > + pid_vnr(pid), rc); > >> > +} > >> > + > >> > +/* > >> > * Process valid CRBs in fault FIFO. > >> > */ > >> > irqreturn_t vas_fault_thread_fn(int irq, void *data) > >> > @@ -111,6 +224,7 @@ irqreturn_t vas_fault_thread_fn(int irq, void *data) > >> > return IRQ_HANDLED; > >> > } > >> > > >> > + update_csb(window, crb); > >> > } while (true); > >> > } > >> > > >> > -- > >> > 1.8.3.1 > >> > >> cheers > > > > > >