[PATCH v4 3.0-rc2-tip 2/22] 2: uprobes: Breakground page replacement.

Srikar Dronamraju
2011-06-07T13:05:31Z

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: 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 | 309 +++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 403 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 26b0e23..3d91687 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..232ccea
--- /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, 2008-2011
+ * 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 2d64cfc..2ca229a 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -107,6 +107,7 @@ obj-$(CONFIG_PERF_EVENTS) += events/
obj-$(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..7ef916e
--- /dev/null
+++ b/kernel/uprobes.c
@@ -0,0 +1,309 @@
+/*
+ * 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, 2008-2011
+ * 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 */
+#include <linux/mmu_notifier.h> /* needed for set_pte_at_notify */
+#include <linux/swap.h> /* needed for try_to_free_swap */
+
+struct uprobe {
+ u8 insn[MAX_UINSN_BYTES];
+ u16 fixups;
+};
+
+static bool valid_vma(struct vm_area_struct *vma)
+{
+ if (!vma->vm_file)
+ return false;
+
+ if ((vma->vm_flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)) ==
+ (VM_READ|VM_EXEC))
+ return true;
+
+ 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_trans_huge(*pmd) || (!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;
+ 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, 1, 1, &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;
+
+ /* 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);
+ kunmap_atomic(vaddr_old);
+
+ ret = anon_vma_prepare(vma);
+ if (ret)
+ 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, KM_USER0);
+ 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_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)
+{
+ pr_warn_once("Can't place breakpoint at pid %d vaddr" " %#lx: %s\n",
+ tsk->pid, vaddr, why);
+}
+
+/**
+ * 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);
+}