Adding support to add special mapping for for user space trampoline with following functions:
uprobe_trampoline_get - find or add uprobe_trampoline uprobe_trampoline_put - remove or destroy uprobe_trampoline The user space trampoline is exported as arch specific user space special mapping through tramp_mapping, which is initialized in following changes with new uprobe syscall. The uprobe trampoline needs to be callable/reachable from the probed address, so while searching for available address we use is_reachable_by_call function to decide if the uprobe trampoline is callable from the probe address. All uprobe_trampoline objects are stored in uprobes_state object and are cleaned up when the process mm_struct goes down. Adding new arch hooks for that, because this change is x86_64 specific. Locking is provided by callers in following changes. Signed-off-by: Jiri Olsa <[email protected]> --- arch/x86/kernel/uprobes.c | 131 ++++++++++++++++++++++++++++++++++++++ include/linux/uprobes.h | 6 ++ kernel/events/uprobes.c | 10 +++ kernel/fork.c | 1 + 4 files changed, 148 insertions(+) diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 77050e5a4680..023c55d52138 100644 --- a/arch/x86/kernel/uprobes.c +++ b/arch/x86/kernel/uprobes.c @@ -608,6 +608,137 @@ static void riprel_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs) *sr = utask->autask.saved_scratch_register; } } + +static int tramp_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma) +{ + return -EPERM; +} + +static struct page *tramp_mapping_pages[2] __ro_after_init; + +static struct vm_special_mapping tramp_mapping = { + .name = "[uprobes-trampoline]", + .mremap = tramp_mremap, + .pages = tramp_mapping_pages, +}; + +struct uprobe_trampoline { + struct hlist_node node; + unsigned long vaddr; + atomic64_t ref; +}; + +static bool is_reachable_by_call(unsigned long vtramp, unsigned long vaddr) +{ + long delta = (long)(vaddr + 5 - vtramp); + + return delta >= INT_MIN && delta <= INT_MAX; +} + +static unsigned long find_nearest_page(unsigned long vaddr) +{ + struct vm_area_struct *vma, *prev = NULL; + unsigned long prev_vm_end = PAGE_SIZE; + VMA_ITERATOR(vmi, current->mm, 0); + + vma = vma_next(&vmi); + while (vma) { + if (prev) + prev_vm_end = prev->vm_end; + if (vma->vm_start - prev_vm_end >= PAGE_SIZE) { + if (is_reachable_by_call(prev_vm_end, vaddr)) + return prev_vm_end; + if (is_reachable_by_call(vma->vm_start - PAGE_SIZE, vaddr)) + return vma->vm_start - PAGE_SIZE; + } + prev = vma; + vma = vma_next(&vmi); + } + + return 0; +} + +static struct uprobe_trampoline *create_uprobe_trampoline(unsigned long vaddr) +{ + struct pt_regs *regs = task_pt_regs(current); + struct mm_struct *mm = current->mm; + struct uprobe_trampoline *tramp; + struct vm_area_struct *vma; + + if (!user_64bit_mode(regs)) + return NULL; + + vaddr = find_nearest_page(vaddr); + if (!vaddr) + return NULL; + + tramp = kzalloc(sizeof(*tramp), GFP_KERNEL); + if (unlikely(!tramp)) + return NULL; + + atomic64_set(&tramp->ref, 1); + tramp->vaddr = vaddr; + + vma = _install_special_mapping(mm, tramp->vaddr, PAGE_SIZE, + VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO, + &tramp_mapping); + if (IS_ERR(vma)) + goto free_area; + return tramp; + +free_area: + kfree(tramp); + return NULL; +} + +__maybe_unused +static struct uprobe_trampoline *uprobe_trampoline_get(unsigned long vaddr) +{ + struct uprobes_state *state = ¤t->mm->uprobes_state; + struct uprobe_trampoline *tramp = NULL; + + hlist_for_each_entry(tramp, &state->head_tramps, node) { + if (is_reachable_by_call(tramp->vaddr, vaddr)) { + atomic64_inc(&tramp->ref); + return tramp; + } + } + + tramp = create_uprobe_trampoline(vaddr); + if (!tramp) + return NULL; + + hlist_add_head(&tramp->node, &state->head_tramps); + return tramp; +} + +static void destroy_uprobe_trampoline(struct uprobe_trampoline *tramp) +{ + hlist_del(&tramp->node); + kfree(tramp); +} + +__maybe_unused +static void uprobe_trampoline_put(struct uprobe_trampoline *tramp) +{ + if (tramp && atomic64_dec_and_test(&tramp->ref)) + destroy_uprobe_trampoline(tramp); +} + +void arch_uprobe_init_state(struct mm_struct *mm) +{ + INIT_HLIST_HEAD(&mm->uprobes_state.head_tramps); +} + +void arch_uprobe_clear_state(struct mm_struct *mm) +{ + struct uprobes_state *state = &mm->uprobes_state; + struct uprobe_trampoline *tramp; + struct hlist_node *n; + + hlist_for_each_entry_safe(tramp, n, &state->head_tramps, node) + destroy_uprobe_trampoline(tramp); +} #else /* 32-bit: */ /* * No RIP-relative addressing on 32-bit diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h index 6af61e977bfb..bc532d086813 100644 --- a/include/linux/uprobes.h +++ b/include/linux/uprobes.h @@ -17,6 +17,7 @@ #include <linux/wait.h> #include <linux/timer.h> #include <linux/seqlock.h> +#include <linux/mutex.h> struct uprobe; struct vm_area_struct; @@ -185,6 +186,9 @@ struct xol_area; struct uprobes_state { struct xol_area *xol_area; +#ifdef CONFIG_X86_64 + struct hlist_head head_tramps; +#endif }; typedef int (*uprobe_write_verify_t)(struct page *page, unsigned long vaddr, @@ -233,6 +237,8 @@ extern void uprobe_handle_trampoline(struct pt_regs *regs); extern void *arch_uretprobe_trampoline(unsigned long *psize); extern unsigned long uprobe_get_trampoline_vaddr(void); extern void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len); +extern void arch_uprobe_clear_state(struct mm_struct *mm); +extern void arch_uprobe_init_state(struct mm_struct *mm); #else /* !CONFIG_UPROBES */ struct uprobes_state { }; diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index d256c695d7ff..a3107f63f295 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1812,6 +1812,14 @@ static struct xol_area *get_xol_area(void) return area; } +void __weak arch_uprobe_clear_state(struct mm_struct *mm) +{ +} + +void __weak arch_uprobe_init_state(struct mm_struct *mm) +{ +} + /* * uprobe_clear_state - Free the area allocated for slots. */ @@ -1823,6 +1831,8 @@ void uprobe_clear_state(struct mm_struct *mm) delayed_uprobe_remove(NULL, mm); mutex_unlock(&delayed_uprobe_lock); + arch_uprobe_clear_state(mm); + if (!area) return; diff --git a/kernel/fork.c b/kernel/fork.c index c4b26cd8998b..4c2df3816728 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1269,6 +1269,7 @@ static void mm_init_uprobes_state(struct mm_struct *mm) { #ifdef CONFIG_UPROBES mm->uprobes_state.xol_area = NULL; + arch_uprobe_init_state(mm); #endif } -- 2.49.0
