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

[Srikar Dronamraju]

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@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jim Keniston <jkenisto@xxxxxxxxxx>
---
 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@xxxxxxxxxxxxxxxx>, 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);
+}
--
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