[PATCH v4 3.0-rc2-tip 6/22] 6: uprobes: store/restore original instruction.

[Srikar Dronamraju]

On the first probe insertion, copy the original instruction and opcode.
If multiple vmas map the same text area corresponding to an inode, we
only need to copy the instruction just once.
The copied instruction is further copied to a designated slot on probe
hit.  Its also used at the time of probe removal to restore the original
instruction.
opcode is used to analyze the instruction and determine the fixups.
Determining fixups at probe hit time would result in doing the same
operation on every probe hit. Hence Instruction analysis using the
opcode is done at probe insertion time.

Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
 kernel/uprobes.c |  121 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 114 insertions(+), 7 deletions(-)

diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index c6c2f5e..9564a78 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -133,6 +133,7 @@ static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
 			unsigned long vaddr, uprobe_opcode_t opcode)
 {
 	struct page *old_page, *new_page;
+	struct address_space *mapping;
 	void *vaddr_old, *vaddr_new;
 	struct vm_area_struct *vma;
 	unsigned long addr;
@@ -153,6 +154,18 @@ static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
 	if (!valid_vma(vma))
 		goto put_out;
 
+	mapping = uprobe->inode->i_mapping;
+	if (mapping != vma->vm_file->f_mapping)
+		goto put_out;
+
+	addr = vma->vm_start + uprobe->offset;
+	addr -= vma->vm_pgoff << PAGE_SHIFT;
+	if (addr > TASK_SIZE_OF(tsk))
+		goto put_out;
+
+	if (vaddr != (unsigned long) addr)
+		goto put_out;
+
 	/* Allocate a page */
 	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
 	if (!new_page) {
@@ -171,7 +184,6 @@ static int write_opcode(struct task_struct *tsk, struct uprobe * uprobe,
 
 	memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
 	/* poke the new insn in, ASSUMES we don't cross page boundary */
-	addr = vaddr;
 	vaddr &= ~PAGE_MASK;
 	memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);
 
@@ -507,6 +519,66 @@ static bool del_consumer(struct uprobe *uprobe,
 	return ret;
 }
 
+static int __copy_insn(struct address_space *mapping,
+			struct vm_area_struct *vma, char *insn,
+			unsigned long nbytes, unsigned long offset)
+{
+	struct file *filp = vma->vm_file;
+	struct page *page;
+	void *vaddr;
+	unsigned long off1;
+	unsigned long idx;
+
+	if (!filp)
+		return -EINVAL;
+
+	idx = (unsigned long) (offset >> PAGE_CACHE_SHIFT);
+	off1 = offset &= ~PAGE_MASK;
+
+	/*
+	 * Ensure that the page that has the original instruction is
+	 * populated and in page-cache.
+	 */
+	page_cache_sync_readahead(mapping, &filp->f_ra, filp, idx, 1);
+	page = grab_cache_page(mapping, idx);
+	if (!page)
+		return -ENOMEM;
+
+	vaddr = kmap_atomic(page, KM_USER0);
+	memcpy(insn, vaddr + off1, nbytes);
+	kunmap_atomic(vaddr);
+	unlock_page(page);
+	page_cache_release(page);
+	return 0;
+}
+
+static int copy_insn(struct uprobe *uprobe, struct vm_area_struct *vma,
+					unsigned long addr)
+{
+	struct address_space *mapping;
+	int bytes;
+	unsigned long nbytes;
+
+	addr &= ~PAGE_MASK;
+	nbytes = PAGE_SIZE - addr;
+	mapping = uprobe->inode->i_mapping;
+
+	/* Instruction at end of binary; copy only available bytes */
+	if (uprobe->offset + MAX_UINSN_BYTES > uprobe->inode->i_size)
+		bytes = uprobe->inode->i_size - uprobe->offset;
+	else
+		bytes = MAX_UINSN_BYTES;
+
+	/* Instruction at the page-boundary; copy bytes in second page */
+	if (nbytes < bytes) {
+		if (__copy_insn(mapping, vma, uprobe->insn + nbytes,
+				bytes - nbytes, uprobe->offset + nbytes))
+			return -ENOMEM;
+		bytes = nbytes;
+	}
+	return __copy_insn(mapping, vma, uprobe->insn, bytes, uprobe->offset);
+}
+
 static struct task_struct *get_mm_owner(struct mm_struct *mm)
 {
 	struct task_struct *tsk;
@@ -521,22 +593,57 @@ static struct task_struct *get_mm_owner(struct mm_struct *mm)
 
 static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe)
 {
-	int ret = 0;
+	struct task_struct *tsk = get_mm_owner(mm);
+	int ret;
 
-	/*TODO: install breakpoint */
-	if (!ret)
+	if (!tsk)	/* task is probably exiting; bail-out */
+		return -ESRCH;
+
+	if (!uprobe->copy) {
+		struct vm_area_struct *vma = find_vma(mm, mm->uprobes_vaddr);
+
+		ret = copy_insn(uprobe, vma, mm->uprobes_vaddr);
+		if (ret)
+			goto put_return;
+		if (is_bkpt_insn(uprobe->insn)) {
+			print_insert_fail(tsk, mm->uprobes_vaddr,
+				"breakpoint instruction already exists");
+			ret = -EEXIST;
+			goto put_return;
+		}
+		ret = analyze_insn(tsk, uprobe);
+		if (ret) {
+			print_insert_fail(tsk, mm->uprobes_vaddr,
+					"instruction type cannot be probed");
+			goto put_return;
+		}
+		uprobe->copy = 1;
+	}
+
+	ret = set_bkpt(tsk, uprobe, mm->uprobes_vaddr);
+	if (ret < 0)
+		print_insert_fail(tsk, mm->uprobes_vaddr,
+					"failed to insert bkpt instruction");
+	else
 		atomic_inc(&mm->uprobes_count);
+
+put_return:
+	put_task_struct(tsk);
 	return ret;
 }
 
 static int __remove_breakpoint(struct mm_struct *mm, struct uprobe *uprobe)
 {
-	int ret = 0;
+	struct task_struct *tsk = get_mm_owner(mm);
+	int ret;
 
-	/*TODO: remove breakpoint */
+	if (!tsk)	/* task is probably exiting; bail-out */
+		return -ESRCH;
+
+	ret = set_orig_insn(tsk, uprobe, mm->uprobes_vaddr, true);
 	if (!ret)
 		atomic_dec(&mm->uprobes_count);
-
+	put_task_struct(tsk);
 	return ret;
 }
 
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