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Subject[PATCH v5 3.1.0-rc4-tip 9/26] Uprobes: Background page replacement.

Provides Background page replacement by
- cow the page that needs replacement.
- modify a copy of the cowed page.
- replace the cow page with the modified page
- flush the page tables.

Also provides additional routines to read an opcode from a given virtual
address and for verifying if a instruction is a breakpoint instruction.

Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
include/linux/uprobes.h | 4 +
kernel/uprobes.c | 268 ++++++++++++++++++++++++++++++++++++++++++++++-
2 files changed, 266 insertions(+), 6 deletions(-)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 2548b94..2c139f3 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -29,6 +29,7 @@ struct vm_area_struct;
#ifdef CONFIG_ARCH_SUPPORTS_UPROBES
#include <asm/uprobes.h>
#else
+typedef u8 uprobe_opcode_t;
struct uprobe_arch_info {};
#define MAX_UINSN_BYTES 4
#endif
@@ -74,6 +75,9 @@ extern int __weak set_bkpt(struct task_struct *tsk, struct uprobe *uprobe,
unsigned long vaddr);
extern int __weak set_orig_insn(struct task_struct *tsk,
struct uprobe *uprobe, unsigned long vaddr, bool verify);
+extern bool __weak is_bkpt_insn(u8 *insn);
+extern int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
+ uprobe_opcode_t *opcode);
extern int register_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer);
extern void unregister_uprobe(struct inode *inode, loff_t offset,
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index e0e10dd..9adc3aa 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -26,6 +26,9 @@
#include <linux/pagemap.h> /* grab_cache_page */
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/rmap.h> /* anon_vma_prepare */
+#include <linux/mmu_notifier.h> /* set_pte_at_notify */
+#include <linux/swap.h> /* try_to_free_swap */
#include <linux/uprobes.h>

static struct rb_root uprobes_tree = RB_ROOT;
@@ -60,18 +63,265 @@ static bool valid_vma(struct vm_area_struct *vma)
return false;
}

+/**
+ * __replace_page - replace page in vma by new page.
+ * based on replace_page in mm/ksm.c
+ *
+ * @vma: vma that holds the pte pointing to page
+ * @page: the cowed page we are replacing by kpage
+ * @kpage: the modified page we replace page by
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ */
+static int __replace_page(struct vm_area_struct *vma, struct page *page,
+ struct page *kpage)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *ptep;
+ spinlock_t *ptl;
+ unsigned long addr;
+ int err = -EFAULT;
+
+ addr = page_address_in_vma(page, vma);
+ if (addr == -EFAULT)
+ goto out;
+
+ pgd = pgd_offset(mm, addr);
+ if (!pgd_present(*pgd))
+ goto out;
+
+ pud = pud_offset(pgd, addr);
+ if (!pud_present(*pud))
+ goto out;
+
+ pmd = pmd_offset(pud, addr);
+ if (!pmd_present(*pmd))
+ goto out;
+
+ ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
+ if (!ptep)
+ goto out;
+
+ get_page(kpage);
+ page_add_new_anon_rmap(kpage, vma, addr);
+
+ flush_cache_page(vma, addr, pte_pfn(*ptep));
+ ptep_clear_flush(vma, addr, ptep);
+ set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
+
+ page_remove_rmap(page);
+ if (!page_mapped(page))
+ try_to_free_swap(page);
+ put_page(page);
+ pte_unmap_unlock(ptep, ptl);
+ err = 0;
+
+out:
+ return err;
+}
+
+/*
+ * NOTE:
+ * Expect the breakpoint instruction to be the smallest size instruction for
+ * the architecture. If an arch has variable length instruction and the
+ * breakpoint instruction is not of the smallest length instruction
+ * supported by that architecture then we need to modify read_opcode /
+ * write_opcode accordingly. This would never be a problem for archs that
+ * have fixed length instructions.
+ */
+
+/*
+ * write_opcode - write the opcode at a given virtual address.
+ * @tsk: the probed task.
+ * @uprobe: the breakpointing information.
+ * @vaddr: the virtual address to store the opcode.
+ * @opcode: opcode to be written at @vaddr.
+ *
+ * Called with tsk->mm->mmap_sem held (for read and with a reference to
+ * tsk->mm).
+ *
+ * For task @tsk, write the opcode at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+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;
+ int ret;
+
+ /* Read the page with vaddr into memory */
+ ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &old_page, &vma);
+ if (ret <= 0)
+ return ret;
+ ret = -EINVAL;
+
+ /*
+ * We are interested in text pages only. Our pages of interest
+ * should be mapped for read and execute only. We desist from
+ * adding probes in write mapped pages since the breakpoints
+ * might end up in the file copy.
+ */
+ 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 (vaddr != (unsigned long) addr)
+ goto put_out;
+
+ /* Allocate a page */
+ new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
+ if (!new_page) {
+ ret = -ENOMEM;
+ goto put_out;
+ }
+
+ /*
+ * lock page will serialize against do_wp_page()'s
+ * PageAnon() handling
+ */
+ lock_page(old_page);
+ /* copy the page now that we've got it stable */
+ vaddr_old = kmap_atomic(old_page);
+ vaddr_new = kmap_atomic(new_page);
+
+ memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
+ /* poke the new insn in, ASSUMES we don't cross page boundary */
+ vaddr &= ~PAGE_MASK;
+ memcpy(vaddr_new + vaddr, &opcode, uprobe_opcode_sz);
+
+ kunmap_atomic(vaddr_new);
+ kunmap_atomic(vaddr_old);
+
+ ret = anon_vma_prepare(vma);
+ if (ret) {
+ page_cache_release(new_page);
+ goto unlock_out;
+ }
+
+ lock_page(new_page);
+ ret = __replace_page(vma, old_page, new_page);
+ unlock_page(new_page);
+ if (ret != 0)
+ page_cache_release(new_page);
+unlock_out:
+ unlock_page(old_page);
+
+put_out:
+ put_page(old_page); /* we did a get_page in the beginning */
+ return ret;
+}
+
+/**
+ * read_opcode - read the opcode at a given virtual address.
+ * @tsk: the probed task.
+ * @vaddr: the virtual address to read the opcode.
+ * @opcode: location to store the read opcode.
+ *
+ * Called with tsk->mm->mmap_sem held (for read and with a reference to
+ * tsk->mm.
+ *
+ * For task @tsk, read the opcode at @vaddr and store it in @opcode.
+ * Return 0 (success) or a negative errno.
+ */
+int __weak read_opcode(struct task_struct *tsk, unsigned long vaddr,
+ uprobe_opcode_t *opcode)
+{
+ struct vm_area_struct *vma;
+ struct page *page;
+ void *vaddr_new;
+ int ret;
+
+ ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 0, 0, &page, &vma);
+ if (ret <= 0)
+ return ret;
+ ret = -EINVAL;
+
+ /*
+ * We are interested in text pages only. Our pages of interest
+ * should be mapped for read and execute only. We desist from
+ * adding probes in write mapped pages since the breakpoints
+ * might end up in the file copy.
+ */
+ if (!valid_vma(vma))
+ goto put_out;
+
+ lock_page(page);
+ vaddr_new = kmap_atomic(page);
+ vaddr &= ~PAGE_MASK;
+ memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz);
+ kunmap_atomic(vaddr_new);
+ unlock_page(page);
+ ret = 0;
+
+put_out:
+ put_page(page); /* we did a get_user_pages in the beginning */
+ return ret;
+}
+
+/**
+ * set_bkpt - store breakpoint at a given address.
+ * @tsk: the probed task.
+ * @uprobe: the probepoint information.
+ * @vaddr: the virtual address to insert the opcode.
+ *
+ * For task @tsk, store the breakpoint instruction at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
int __weak set_bkpt(struct task_struct *tsk, struct uprobe *uprobe,
unsigned long vaddr)
{
- /* placeholder: yet to be implemented */
- return 0;
+ return write_opcode(tsk, uprobe, vaddr, UPROBES_BKPT_INSN);
}

+/**
+ * set_orig_insn - Restore the original instruction.
+ * @tsk: the probed task.
+ * @uprobe: the probepoint information.
+ * @vaddr: the virtual address to insert the opcode.
+ * @verify: if true, verify existance of breakpoint instruction.
+ *
+ * For task @tsk, restore the original opcode (opcode) at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
int __weak set_orig_insn(struct task_struct *tsk, struct uprobe *uprobe,
- unsigned long vaddr, bool verify)
+ unsigned long vaddr, bool verify)
{
- /* placeholder: yet to be implemented */
- return 0;
+ if (verify) {
+ uprobe_opcode_t opcode;
+ int result = read_opcode(tsk, vaddr, &opcode);
+ if (result)
+ return result;
+ if (opcode != UPROBES_BKPT_INSN)
+ return -EINVAL;
+ }
+ return write_opcode(tsk, uprobe, vaddr,
+ *(uprobe_opcode_t *) uprobe->insn);
+}
+
+/**
+ * is_bkpt_insn - check if instruction is breakpoint instruction.
+ * @insn: instruction to be checked.
+ * Default implementation of is_bkpt_insn
+ * Returns true if @insn is a breakpoint instruction.
+ */
+bool __weak is_bkpt_insn(u8 *insn)
+{
+ uprobe_opcode_t opcode;
+
+ memcpy(&opcode, insn, UPROBES_BKPT_INSN_SIZE);
+ return (opcode == UPROBES_BKPT_INSN);
}

static int match_uprobe(struct uprobe *l, struct uprobe *r, int *match_inode)
@@ -357,7 +607,13 @@ static int install_breakpoint(struct mm_struct *mm, struct uprobe *uprobe,
ret = copy_insn(uprobe, vma, addr);
if (ret)
goto put_return;
- /* TODO : Analysis and verification of instruction */
+ if (is_bkpt_insn(uprobe->insn)) {
+ ret = -EEXIST;
+ goto put_return;
+ }
+ ret = analyze_insn(tsk, uprobe);
+ if (ret)
+ goto put_return;
uprobe->copy = 1;
}


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