From 69b0475456ff7ef520e16f69d7a15c0d68b74e64 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Sat, 29 Oct 2005 18:16:36 -0700 Subject: [PATCH] mm: arm ready for split ptlock Prepare arm for the split page_table_lock: three issues. Signal handling's preserve and restore of iwmmxt context currently involves reading and writing that context to and from user space, while holding page_table_lock to secure the user page(s) against kswapd. If we split the lock, then the structure might span two pages, secured by to read into and write from a kernel stack buffer, copying that out and in without locking (the structure is 160 bytes in size, and here we're near the top of the kernel stack). Or would the overhead be noticeable? arm_syscall's cmpxchg emulation use pte_offset_map_lock, instead of pte_offset_map and mm-wide page_table_lock; and strictly, it should now also take mmap_sem before descending to pmd, to guard against another thread munmapping, and the page table pulled out beneath this thread. Updated two comments in fault-armv.c. adjust_pte is interesting, since its modification of a pte in one part of the mm depends on the lock held when calling update_mmu_cache for a pte in some other part of that mm. This can't be done with a split page_table_lock (and we've already taken the lowest lock in the hierarchy here): so we'll have to disable split on arm, unless CONFIG_CPU_CACHE_VIPT to ensures adjust_pte never used. Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/arm/kernel/signal.c | 96 +++++++++--------------------------------------- 1 file changed, 18 insertions(+), 78 deletions(-) (limited to 'arch/arm/kernel/signal.c') diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c index a94d75fef598..a917e3dd3666 100644 --- a/arch/arm/kernel/signal.c +++ b/arch/arm/kernel/signal.c @@ -139,93 +139,33 @@ struct iwmmxt_sigframe { unsigned long storage[0x98/4]; }; -static int page_present(struct mm_struct *mm, void __user *uptr, int wr) -{ - unsigned long addr = (unsigned long)uptr; - pgd_t *pgd = pgd_offset(mm, addr); - if (pgd_present(*pgd)) { - pmd_t *pmd = pmd_offset(pgd, addr); - if (pmd_present(*pmd)) { - pte_t *pte = pte_offset_map(pmd, addr); - return (pte_present(*pte) && (!wr || pte_write(*pte))); - } - } - return 0; -} - -static int copy_locked(void __user *uptr, void *kptr, size_t size, int write, - void (*copyfn)(void *, void __user *)) -{ - unsigned char v, __user *userptr = uptr; - int err = 0; - - do { - struct mm_struct *mm; - - if (write) { - __put_user_error(0, userptr, err); - __put_user_error(0, userptr + size - 1, err); - } else { - __get_user_error(v, userptr, err); - __get_user_error(v, userptr + size - 1, err); - } - - if (err) - break; - - mm = current->mm; - spin_lock(&mm->page_table_lock); - if (page_present(mm, userptr, write) && - page_present(mm, userptr + size - 1, write)) { - copyfn(kptr, uptr); - } else - err = 1; - spin_unlock(&mm->page_table_lock); - } while (err); - - return err; -} - static int preserve_iwmmxt_context(struct iwmmxt_sigframe *frame) { - int err = 0; + char kbuf[sizeof(*frame) + 8]; + struct iwmmxt_sigframe *kframe; /* the iWMMXt context must be 64 bit aligned */ - WARN_ON((unsigned long)frame & 7); - - __put_user_error(IWMMXT_MAGIC0, &frame->magic0, err); - __put_user_error(IWMMXT_MAGIC1, &frame->magic1, err); - - /* - * iwmmxt_task_copy() doesn't check user permissions. - * Let's do a dummy write on the upper boundary to ensure - * access to user mem is OK all way up. - */ - err |= copy_locked(&frame->storage, current_thread_info(), - sizeof(frame->storage), 1, iwmmxt_task_copy); - return err; + kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7); + kframe->magic0 = IWMMXT_MAGIC0; + kframe->magic1 = IWMMXT_MAGIC1; + iwmmxt_task_copy(current_thread_info(), &kframe->storage); + return __copy_to_user(frame, kframe, sizeof(*frame)); } static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame) { - unsigned long magic0, magic1; - int err = 0; + char kbuf[sizeof(*frame) + 8]; + struct iwmmxt_sigframe *kframe; - /* the iWMMXt context is 64 bit aligned */ - WARN_ON((unsigned long)frame & 7); - - /* - * Validate iWMMXt context signature. - * Also, iwmmxt_task_restore() doesn't check user permissions. - * Let's do a dummy write on the upper boundary to ensure - * access to user mem is OK all way up. - */ - __get_user_error(magic0, &frame->magic0, err); - __get_user_error(magic1, &frame->magic1, err); - if (!err && magic0 == IWMMXT_MAGIC0 && magic1 == IWMMXT_MAGIC1) - err = copy_locked(&frame->storage, current_thread_info(), - sizeof(frame->storage), 0, iwmmxt_task_restore); - return err; + /* the iWMMXt context must be 64 bit aligned */ + kframe = (struct iwmmxt_sigframe *)((unsigned long)(kbuf + 8) & ~7); + if (__copy_from_user(kframe, frame, sizeof(*frame))) + return -1; + if (kframe->magic0 != IWMMXT_MAGIC0 || + kframe->magic1 != IWMMXT_MAGIC1) + return -1; + iwmmxt_task_restore(current_thread_info(), &kframe->storage); + return 0; } #endif -- cgit v1.2.3