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    Subject[PATCH v3 2.6.39-rc1-tip 4/26] 4: uprobes: Breakground page replacement.

    Provides Background page replacement using replace_page() routine.
    Also provides routines to read an opcode from a given virtual address
    and for verifying if a instruction is a breakpoint instruction.

    Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
    ---
    arch/Kconfig | 12 ++
    include/linux/uprobes.h | 81 +++++++++++++++
    kernel/Makefile | 1
    kernel/uprobes.c | 254 +++++++++++++++++++++++++++++++++++++++++++++++
    4 files changed, 348 insertions(+), 0 deletions(-)
    create mode 100644 include/linux/uprobes.h
    create mode 100644 kernel/uprobes.c

    diff --git a/arch/Kconfig b/arch/Kconfig
    index f78c2be..c681f16 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -61,6 +61,18 @@ config OPTPROBES
    depends on KPROBES && HAVE_OPTPROBES
    depends on !PREEMPT

    +config UPROBES
    + bool "User-space probes (EXPERIMENTAL)"
    + depends on ARCH_SUPPORTS_UPROBES
    + depends on MMU
    + select MM_OWNER
    + help
    + Uprobes enables kernel subsystems to establish probepoints
    + in user applications and execute handler functions when
    + the probepoints are hit.
    +
    + If in doubt, say "N".
    +
    config HAVE_EFFICIENT_UNALIGNED_ACCESS
    bool
    help
    diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
    new file mode 100644
    index 0000000..ae134a5
    --- /dev/null
    +++ b/include/linux/uprobes.h
    @@ -0,0 +1,81 @@
    +#ifndef _LINUX_UPROBES_H
    +#define _LINUX_UPROBES_H
    +/*
    + * Userspace Probes (UProbes)
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License as published by
    + * the Free Software Foundation; either version 2 of the License, or
    + * (at your option) any later version.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + *
    + * You should have received a copy of the GNU General Public License
    + * along with this program; if not, write to the Free Software
    + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
    + *
    + * Copyright (C) IBM Corporation, 2008-2010
    + * Authors:
    + * Srikar Dronamraju
    + * Jim Keniston
    + */
    +
    +#ifdef CONFIG_ARCH_SUPPORTS_UPROBES
    +#include <asm/uprobes.h>
    +#else
    +/*
    + * ARCH_SUPPORTS_UPROBES is not defined.
    + */
    +typedef u8 uprobe_opcode_t;
    +#endif /* CONFIG_ARCH_SUPPORTS_UPROBES */
    +
    +/* Post-execution fixups. Some architectures may define others. */
    +
    +/* No fixup needed */
    +#define UPROBES_FIX_NONE 0x0
    +/* Adjust IP back to vicinity of actual insn */
    +#define UPROBES_FIX_IP 0x1
    +/* Adjust the return address of a call insn */
    +#define UPROBES_FIX_CALL 0x2
    +/* Might sleep while doing Fixup */
    +#define UPROBES_FIX_SLEEPY 0x4
    +
    +#ifndef UPROBES_FIX_DEFAULT
    +#define UPROBES_FIX_DEFAULT UPROBES_FIX_IP
    +#endif
    +
    +/* Unexported functions & macros for use by arch-specific code */
    +#define uprobe_opcode_sz (sizeof(uprobe_opcode_t))
    +
    +/*
    + * Most architectures can use the default versions of @read_opcode(),
    + * @set_bkpt(), @set_orig_insn(), and @is_bkpt_insn();
    + *
    + * @set_ip:
    + * Set the instruction pointer in @regs to @vaddr.
    + * @analyze_insn:
    + * Analyze @user_bkpt->insn. Return 0 if @user_bkpt->insn is an
    + * instruction you can probe, or a negative errno (typically -%EPERM)
    + * otherwise. Determine what sort of XOL-related fixups @post_xol()
    + * (and possibly @pre_xol()) will need to do for this instruction, and
    + * annotate @user_bkpt accordingly. You may modify @user_bkpt->insn
    + * (e.g., the x86_64 port does this for rip-relative instructions).
    + * @pre_xol:
    + * Called just before executing the instruction associated
    + * with @user_bkpt out of line. @user_bkpt->xol_vaddr is the address
    + * in @tsk's virtual address space where @user_bkpt->insn has been
    + * copied. @pre_xol() should at least set the instruction pointer in
    + * @regs to @user_bkpt->xol_vaddr -- which is what the default,
    + * @pre_xol(), does.
    + * @post_xol:
    + * Called after executing the instruction associated with
    + * @user_bkpt out of line. @post_xol() should perform the fixups
    + * specified in @user_bkpt->fixups, which includes ensuring that the
    + * instruction pointer in @regs points at the next instruction in
    + * the probed instruction stream. @tskinfo is as for @pre_xol().
    + * You must provide this function.
    + */
    +#endif /* _LINUX_UPROBES_H */
    diff --git a/kernel/Makefile b/kernel/Makefile
    index 85cbfb3..7c26588 100644
    --- a/kernel/Makefile
    +++ b/kernel/Makefile
    @@ -108,6 +108,7 @@ obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
    obj-$(CONFIG_USER_RETURN_NOTIFIER) += user-return-notifier.o
    obj-$(CONFIG_PADATA) += padata.o
    obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
    +obj-$(CONFIG_UPROBES) += uprobes.o

    ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
    # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
    diff --git a/kernel/uprobes.c b/kernel/uprobes.c
    new file mode 100644
    index 0000000..9ef21a7
    --- /dev/null
    +++ b/kernel/uprobes.c
    @@ -0,0 +1,254 @@
    +/*
    + * Userspace Probes (UProbes)
    + *
    + * This program is free software; you can redistribute it and/or modify
    + * it under the terms of the GNU General Public License as published by
    + * the Free Software Foundation; either version 2 of the License, or
    + * (at your option) any later version.
    + *
    + * This program is distributed in the hope that it will be useful,
    + * but WITHOUT ANY WARRANTY; without even the implied warranty of
    + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    + * GNU General Public License for more details.
    + *
    + * You should have received a copy of the GNU General Public License
    + * along with this program; if not, write to the Free Software
    + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
    + *
    + * Copyright (C) IBM Corporation, 2008-2010
    + * Authors:
    + * Srikar Dronamraju
    + * Jim Keniston
    + */
    +#include <linux/kernel.h>
    +#include <linux/init.h>
    +#include <linux/module.h>
    +#include <linux/sched.h>
    +#include <linux/ptrace.h>
    +#include <linux/mm.h>
    +#include <linux/highmem.h>
    +#include <linux/pagemap.h>
    +#include <linux/slab.h>
    +#include <linux/uprobes.h>
    +#include <linux/rmap.h> /* needed for anon_vma_prepare */
    +
    +struct uprobe {
    + u8 insn[MAX_UINSN_BYTES];
    + u16 fixups;
    +};
    +
    +/*
    + * 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 arch's 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;
    + void *vaddr_old, *vaddr_new;
    + struct vm_area_struct *vma;
    + spinlock_t *ptl;
    + pte_t *orig_pte;
    + unsigned long addr;
    + int ret;
    +
    + /* Read the page with vaddr into memory */
    + ret = get_user_pages(tsk, tsk->mm, vaddr, 1, 1, 1, &old_page, &vma);
    + if (ret <= 0)
    + return -EINVAL;
    + 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 ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) !=
    + (VM_READ|VM_EXEC))
    + 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, KM_USER0);
    + vaddr_new = kmap_atomic(new_page, KM_USER1);
    +
    + 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);
    +
    + kunmap_atomic(vaddr_new, KM_USER1);
    + kunmap_atomic(vaddr_old, KM_USER0);
    +
    + orig_pte = page_check_address(old_page, tsk->mm, addr, &ptl, 0);
    + if (!orig_pte)
    + goto unlock_out;
    + pte_unmap_unlock(orig_pte, ptl);
    +
    + lock_page(new_page);
    + ret = anon_vma_prepare(vma);
    + if (!ret)
    + ret = replace_page(vma, old_page, new_page, *orig_pte);
    +
    + 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 -EFAULT;
    + ret = -EFAULT;
    +
    + /*
    + * 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 ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) !=
    + (VM_READ|VM_EXEC))
    + goto put_out;
    +
    + lock_page(page);
    + vaddr_new = kmap_atomic(page, KM_USER0);
    + vaddr &= ~PAGE_MASK;
    + memcpy(opcode, vaddr_new + vaddr, uprobe_opcode_sz);
    + kunmap_atomic(vaddr_new, KM_USER0);
    + unlock_page(page);
    + ret = 0;
    +
    +put_out:
    + put_page(page); /* we did a get_page 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)
    +{
    + 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)
    +{
    + 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);
    +}
    +
    +static void print_insert_fail(struct task_struct *tsk,
    + unsigned long vaddr, const char *why)
    +{
    + printk(KERN_ERR "Can't place breakpoint at pid %d vaddr %#lx: %s\n",
    + tsk->pid, vaddr, why);
    +}
    +
    +/*
    + * uprobes_resume_can_sleep - Check if fixup might result in sleep.
    + * @uprobes: the probepoint information.
    + *
    + * Returns true if fixup might result in sleep.
    + */
    +static bool uprobes_resume_can_sleep(struct uprobe *uprobe)
    +{
    + return uprobe->fixups & UPROBES_FIX_SLEEPY;
    +}
    +
    +/**
    + * 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);
    +}

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