Adding interface to add special mapping for user space page that will be used as place holder for uprobe trampoline in following changes.
The get_tramp_area(vaddr) function either finds 'callable' page or create new one. The 'callable' means it's reachable by call instruction (from vaddr argument) and is decided by each arch via new arch_uprobe_is_callable function. The put_tramp_area function either drops refcount or destroys the special mapping and all the maps are clean up when the process goes down. Signed-off-by: Jiri Olsa <[email protected]> --- include/linux/uprobes.h | 12 ++++ kernel/events/uprobes.c | 141 ++++++++++++++++++++++++++++++++++++++++ kernel/fork.c | 2 + 3 files changed, 155 insertions(+) diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h index be306028ed59..222d8e82cee2 100644 --- a/include/linux/uprobes.h +++ b/include/linux/uprobes.h @@ -172,6 +172,15 @@ struct xol_area; struct uprobes_state { struct xol_area *xol_area; + struct hlist_head tramp_head; + struct mutex tramp_mutex; +}; + +struct tramp_area { + unsigned long vaddr; + struct page *page; + struct hlist_node node; + refcount_t ref; }; extern void __init uprobes_init(void); @@ -219,6 +228,9 @@ extern int uprobe_verify_opcode(struct page *page, unsigned long vaddr, uprobe_o extern int arch_uprobe_verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode, void *data); extern bool arch_uprobe_is_register(uprobe_opcode_t *insn, int len, void *data); +struct tramp_area *get_tramp_area(unsigned long vaddr); +void put_tramp_area(struct tramp_area *area); +bool arch_uprobe_is_callable(unsigned long vtramp, unsigned long vaddr); #else /* !CONFIG_UPROBES */ struct uprobes_state { }; diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 944d9df1f081..a44305c559a4 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -616,6 +616,145 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v (uprobe_opcode_t *)&auprobe->insn, UPROBE_SWBP_INSN_SIZE, NULL); } +bool __weak arch_uprobe_is_callable(unsigned long vtramp, unsigned long vaddr) +{ + return false; +} + +static unsigned long find_nearest_page(unsigned long vaddr) +{ + struct mm_struct *mm = current->mm; + struct vm_area_struct *vma, *prev; + VMA_ITERATOR(vmi, mm, 0); + + prev = vma_next(&vmi); + vma = vma_next(&vmi); + while (vma) { + if (vma->vm_start - prev->vm_end >= PAGE_SIZE && + arch_uprobe_is_callable(prev->vm_end, vaddr)) + return prev->vm_end; + + prev = vma; + vma = vma_next(&vmi); + } + + return 0; +} + +static vm_fault_t tramp_fault(const struct vm_special_mapping *sm, + struct vm_area_struct *vma, struct vm_fault *vmf) +{ + struct hlist_head *head = &vma->vm_mm->uprobes_state.tramp_head; + struct tramp_area *area; + + hlist_for_each_entry(area, head, node) { + if (vma->vm_start == area->vaddr) { + vmf->page = area->page; + get_page(vmf->page); + return 0; + } + } + + return -EINVAL; +} + +static int tramp_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma) +{ + return -EPERM; +} + +static const struct vm_special_mapping tramp_mapping = { + .name = "[uprobes-trampoline]", + .fault = tramp_fault, + .mremap = tramp_mremap, +}; + +static struct tramp_area *create_tramp_area(unsigned long vaddr) +{ + struct mm_struct *mm = current->mm; + struct vm_area_struct *vma; + struct tramp_area *area; + + vaddr = find_nearest_page(vaddr); + if (!vaddr) + return NULL; + + area = kzalloc(sizeof(*area), GFP_KERNEL); + if (unlikely(!area)) + return NULL; + + area->page = alloc_page(GFP_HIGHUSER); + if (!area->page) + goto free_area; + + refcount_set(&area->ref, 1); + area->vaddr = vaddr; + + vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE, + VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO, + &tramp_mapping); + if (!IS_ERR(vma)) + return area; + + __free_page(area->page); + free_area: + kfree(area); + return NULL; +} + +struct tramp_area *get_tramp_area(unsigned long vaddr) +{ + struct uprobes_state *state = ¤t->mm->uprobes_state; + struct tramp_area *area = NULL; + + mutex_lock(&state->tramp_mutex); + hlist_for_each_entry(area, &state->tramp_head, node) { + if (arch_uprobe_is_callable(area->vaddr, vaddr)) { + refcount_inc(&area->ref); + goto unlock; + } + } + + area = create_tramp_area(vaddr); + if (area) + hlist_add_head(&area->node, &state->tramp_head); + +unlock: + mutex_unlock(&state->tramp_mutex); + return area; +} + +static void destroy_tramp_area(struct tramp_area *area) +{ + hlist_del(&area->node); + put_page(area->page); + kfree(area); +} + +void put_tramp_area(struct tramp_area *area) +{ + struct mm_struct *mm = current->mm; + struct uprobes_state *state = &mm->uprobes_state; + + if (area == NULL) + return; + + mutex_lock(&state->tramp_mutex); + if (refcount_dec_and_test(&area->ref)) + destroy_tramp_area(area); + mutex_unlock(&state->tramp_mutex); +} + +static void clear_tramp_head(struct mm_struct *mm) +{ + struct uprobes_state *state = &mm->uprobes_state; + struct tramp_area *area; + struct hlist_node *n; + + hlist_for_each_entry_safe(area, n, &state->tramp_head, node) + destroy_tramp_area(area); +} + /* uprobe should have guaranteed positive refcount */ static struct uprobe *get_uprobe(struct uprobe *uprobe) { @@ -1788,6 +1927,8 @@ void uprobe_clear_state(struct mm_struct *mm) delayed_uprobe_remove(NULL, mm); mutex_unlock(&delayed_uprobe_lock); + clear_tramp_head(mm); + if (!area) return; diff --git a/kernel/fork.c b/kernel/fork.c index 89ceb4a68af2..b1fe431e5cce 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1248,6 +1248,8 @@ static void mm_init_uprobes_state(struct mm_struct *mm) { #ifdef CONFIG_UPROBES mm->uprobes_state.xol_area = NULL; + mutex_init(&mm->uprobes_state.tramp_mutex); + INIT_HLIST_HEAD(&mm->uprobes_state.tramp_head); #endif } -- 2.47.0
