Commit 91440ff4 authored by Jiri Olsa's avatar Jiri Olsa Committed by Peter Zijlstra
Browse files

uprobes/x86: Add mapping for optimized uprobe trampolines 



Adding support to add special mapping 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: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/20250720112133.244369-9-jolsa@kernel.org
parent 18a11125

arch/x86/kernel/uprobes.c

+144 −0
Original line number Diff line number Diff line
@@ -608,6 +608,150 @@ 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;

};



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_trampoline(unsigned long vaddr)

{

	struct vm_unmapped_area_info info = {

		.length     = PAGE_SIZE,

		.align_mask = ~PAGE_MASK,

	};

	unsigned long low_limit, high_limit;

	unsigned long low_tramp, high_tramp;

	unsigned long call_end = vaddr + 5;



	if (check_add_overflow(call_end, INT_MIN, &low_limit))

		low_limit = PAGE_SIZE;



	high_limit = call_end + INT_MAX;



	/* Search up from the caller address. */

	info.low_limit = call_end;

	info.high_limit = min(high_limit, TASK_SIZE);

	high_tramp = vm_unmapped_area(&info);



	/* Search down from the caller address. */

	info.low_limit = max(low_limit, PAGE_SIZE);

	info.high_limit = call_end;

	info.flags = VM_UNMAPPED_AREA_TOPDOWN;

	low_tramp = vm_unmapped_area(&info);



	if (IS_ERR_VALUE(high_tramp) && IS_ERR_VALUE(low_tramp))

		return -ENOMEM;

	if (IS_ERR_VALUE(high_tramp))

		return low_tramp;

	if (IS_ERR_VALUE(low_tramp))

		return high_tramp;



	/* Return address that's closest to the caller address. */

	if (call_end - low_tramp < high_tramp - call_end)

		return low_tramp;

	return high_tramp;

}



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_trampoline(vaddr);

	if (IS_ERR_VALUE(vaddr))

		return NULL;



	tramp = kzalloc(sizeof(*tramp), GFP_KERNEL);

	if (unlikely(!tramp))

		return NULL;



	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)) {

		kfree(tramp);

		return NULL;

	}

	return tramp;

}



__maybe_unused

static struct uprobe_trampoline *get_uprobe_trampoline(unsigned long vaddr, bool *new)

{

	struct uprobes_state *state = &current->mm->uprobes_state;

	struct uprobe_trampoline *tramp = NULL;



	if (vaddr > TASK_SIZE || vaddr < PAGE_SIZE)

		return NULL;



	hlist_for_each_entry(tramp, &state->head_tramps, node) {

		if (is_reachable_by_call(tramp->vaddr, vaddr)) {

			*new = false;

			return tramp;

		}

	}



	tramp = create_uprobe_trampoline(vaddr);

	if (!tramp)

		return NULL;



	*new = true;

	hlist_add_head(&tramp->node, &state->head_tramps);

	return tramp;

}



static void destroy_uprobe_trampoline(struct uprobe_trampoline *tramp)

{

	/*

	 * We do not unmap and release uprobe trampoline page itself,

	 * because there's no easy way to make sure none of the threads

	 * is still inside the trampoline.

	 */

	hlist_del(&tramp->node);

	kfree(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

include/linux/uprobes.h

+6 −0
Original line number Diff line number Diff line
@@ -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 {

};

kernel/events/uprobes.c

+10 −0
Original line number Diff line number Diff line
@@ -1801,6 +1801,14 @@ 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.

 */
@@ -1812,6 +1820,8 @@ 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;

kernel/fork.c

+1 −0
Original line number Diff line number Diff line
@@ -1015,6 +1015,7 @@ 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

}