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Subject[PATCH v5 3.1.0-rc4-tip 12/26] Uprobes: Handle breakpoint and Singlestep

Provides routines to create/manage and free the task specific
information.

Adds a hook in uprobe_notify_resume to handle breakpoint and singlestep
exception.

Uprobes needs to maintain some task specific information including if a
task has hit a probepoint, uprobe corresponding to the probehit,
the slot where the original instruction is copied to before
single-stepping.

Signed-off-by: Jim Keniston <jkenisto@us.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
include/linux/sched.h | 3 +
include/linux/uprobes.h | 35 ++++++++
kernel/fork.c | 4 +
kernel/uprobes.c | 205 +++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 247 insertions(+), 0 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index bc6f5f2..4f84980 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1569,6 +1569,9 @@ struct task_struct {
#ifdef CONFIG_HAVE_HW_BREAKPOINT
atomic_t ptrace_bp_refcnt;
#endif
+#ifdef CONFIG_UPROBES
+ struct uprobe_task *utask;
+#endif
};

/* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 2c139f3..fa7eaba 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -70,6 +70,26 @@ struct uprobe {
u8 insn[MAX_UINSN_BYTES];
};

+enum uprobe_task_state {
+ UTASK_RUNNING,
+ UTASK_BP_HIT,
+ UTASK_SSTEP
+};
+
+/*
+ * uprobe_utask -- not a user-visible struct.
+ * Corresponds to a thread in a probed process.
+ * Guarded by uproc->mutex.
+ */
+struct uprobe_task {
+ unsigned long xol_vaddr;
+ unsigned long vaddr;
+
+ enum uprobe_task_state state;
+
+ struct uprobe *active_uprobe;
+};
+
#ifdef CONFIG_UPROBES
extern int __weak set_bkpt(struct task_struct *tsk, struct uprobe *uprobe,
unsigned long vaddr);
@@ -82,8 +102,13 @@ extern int register_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer);
extern void unregister_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer);
+extern void free_uprobe_utask(struct task_struct *tsk);
extern int mmap_uprobe(struct vm_area_struct *vma);
extern void munmap_uprobe(struct vm_area_struct *vma);
+extern unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs);
+extern int uprobe_post_notifier(struct pt_regs *regs);
+extern int uprobe_bkpt_notifier(struct pt_regs *regs);
+extern void uprobe_notify_resume(struct pt_regs *regs);
#else /* CONFIG_UPROBES is not defined */
static inline int register_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer)
@@ -101,5 +126,15 @@ static inline int mmap_uprobe(struct vm_area_struct *vma)
static inline void munmap_uprobe(struct vm_area_struct *vma)
{
}
+static inline void uprobe_notify_resume(struct pt_regs *regs)
+{
+}
+static inline unsigned long get_uprobe_bkpt_addr(struct pt_regs *regs)
+{
+ return 0;
+}
+static inline void free_uprobe_utask(struct task_struct *tsk)
+{
+}
#endif /* CONFIG_UPROBES */
#endif /* _LINUX_UPROBES_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 7cc0b51..5914bc1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -195,6 +195,7 @@ void __put_task_struct(struct task_struct *tsk)
delayacct_tsk_free(tsk);
put_signal_struct(tsk->signal);

+ free_uprobe_utask(tsk);
if (!profile_handoff_task(tsk))
free_task(tsk);
}
@@ -1285,6 +1286,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
INIT_LIST_HEAD(&p->pi_state_list);
p->pi_state_cache = NULL;
#endif
+#ifdef CONFIG_UPROBES
+ p->utask = NULL;
+#endif
/*
* sigaltstack should be cleared when sharing the same VM
*/
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 9adc3aa..8b6654e 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -29,6 +29,7 @@
#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/ptrace.h> /* user_enable_single_step */
#include <linux/uprobes.h>

static struct rb_root uprobes_tree = RB_ROOT;
@@ -473,6 +474,21 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
return uprobe;
}

+static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+{
+ struct uprobe_consumer *consumer;
+
+ down_read(&uprobe->consumer_rwsem);
+ consumer = uprobe->consumers;
+ for (consumer = uprobe->consumers; consumer;
+ consumer = consumer->next) {
+ if (!consumer->filter ||
+ consumer->filter(consumer, current))
+ consumer->handler(consumer, regs);
+ }
+ up_read(&uprobe->consumer_rwsem);
+}
+
/* Returns the previous consumer */
static struct uprobe_consumer *add_consumer(struct uprobe *uprobe,
struct uprobe_consumer *consumer)
@@ -640,10 +656,22 @@ static void remove_breakpoint(struct mm_struct *mm, struct uprobe *uprobe,
put_task_struct(tsk);
}

+/*
+ * There could be threads that have hit the breakpoint and are entering the
+ * notifier code and trying to acquire the uprobes_treelock. The thread
+ * calling delete_uprobe() that is removing the uprobe from the rb_tree can
+ * race with these threads and might acquire the uprobes_treelock compared
+ * to some of the breakpoint hit threads. In such a case, the breakpoint hit
+ * threads will not find the uprobe. Finding if a "trap" instruction was
+ * present at the interrupting address is racy. Hence provide some extra
+ * time (by way of synchronize_sched() for breakpoint hit threads to acquire
+ * the uprobes_treelock before the uprobe is removed from the rbtree.
+ */
static void delete_uprobe(struct uprobe *uprobe)
{
unsigned long flags;

+ synchronize_sched();
spin_lock_irqsave(&uprobes_treelock, flags);
rb_erase(&uprobe->rb_node, &uprobes_tree);
spin_unlock_irqrestore(&uprobes_treelock, flags);
@@ -1004,3 +1032,180 @@ void munmap_uprobe(struct vm_area_struct *vma)
iput(inode);
return;
}
+
+/**
+ * get_uprobe_bkpt_addr - compute address of bkpt given post-bkpt regs
+ * @regs: Reflects the saved state of the task after it has hit a breakpoint
+ * instruction.
+ * Return the address of the breakpoint instruction.
+ */
+unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs)
+{
+ return instruction_pointer(regs) - UPROBES_BKPT_INSN_SIZE;
+}
+
+/*
+ * Called with no locks held.
+ * Called in context of a exiting or a exec-ing thread.
+ */
+void free_uprobe_utask(struct task_struct *tsk)
+{
+ struct uprobe_task *utask = tsk->utask;
+
+ if (!utask)
+ return;
+
+ if (utask->active_uprobe)
+ put_uprobe(utask->active_uprobe);
+
+ kfree(utask);
+ tsk->utask = NULL;
+}
+
+/*
+ * Allocate a uprobe_task object for the task.
+ * Called when the thread hits a breakpoint for the first time.
+ *
+ * Returns:
+ * - pointer to new uprobe_task on success
+ * - negative errno otherwise
+ */
+static struct uprobe_task *add_utask(void)
+{
+ struct uprobe_task *utask;
+
+ utask = kzalloc(sizeof *utask, GFP_KERNEL);
+ if (unlikely(utask == NULL))
+ return ERR_PTR(-ENOMEM);
+
+ utask->active_uprobe = NULL;
+ current->utask = utask;
+ return utask;
+}
+
+/* Prepare to single-step probed instruction out of line. */
+static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs,
+ unsigned long vaddr)
+{
+ /* TODO: Yet to be implemented */
+ return -EFAULT;
+}
+
+/*
+ * Verify from Instruction Pointer if singlestep has indeed occurred.
+ * If Singlestep has occurred, then do post singlestep fix-ups.
+ */
+static bool sstep_complete(struct uprobe *uprobe, struct pt_regs *regs)
+{
+ /* TODO: Yet to be implemented */
+ return false;
+}
+
+/*
+ * uprobe_notify_resume gets called in task context just before returning
+ * to userspace.
+ *
+ * If its the first time the probepoint is hit, slot gets allocated here.
+ * If its the first time the thread hit a breakpoint, utask gets
+ * allocated here.
+ */
+void uprobe_notify_resume(struct pt_regs *regs)
+{
+ struct vm_area_struct *vma;
+ struct uprobe_task *utask;
+ struct mm_struct *mm;
+ struct uprobe *u = NULL;
+ unsigned long probept;
+
+ utask = current->utask;
+ mm = current->mm;
+ if (!utask || utask->state == UTASK_BP_HIT) {
+ probept = get_uprobe_bkpt_addr(regs);
+ down_read(&mm->mmap_sem);
+ vma = find_vma(mm, probept);
+ if (vma && valid_vma(vma))
+ u = find_uprobe(vma->vm_file->f_mapping->host,
+ probept - vma->vm_start +
+ (vma->vm_pgoff << PAGE_SHIFT));
+ up_read(&mm->mmap_sem);
+ if (!u)
+ /* No matching uprobe; signal SIGTRAP. */
+ goto cleanup_ret;
+ if (!utask) {
+ utask = add_utask();
+ /* Cannot Allocate; re-execute the instruction. */
+ if (!utask)
+ goto cleanup_ret;
+ }
+ /* TODO Start queueing signals. */
+ utask->active_uprobe = u;
+ handler_chain(u, regs);
+ utask->state = UTASK_SSTEP;
+ if (!pre_ssout(u, regs, probept))
+ user_enable_single_step(current);
+ else
+ /* Cannot Singlestep; re-execute the instruction. */
+ goto cleanup_ret;
+ } else if (utask->state == UTASK_SSTEP) {
+ u = utask->active_uprobe;
+ if (sstep_complete(u, regs)) {
+ put_uprobe(u);
+ utask->active_uprobe = NULL;
+ utask->state = UTASK_RUNNING;
+ user_disable_single_step(current);
+
+ /* TODO Stop queueing signals. */
+ }
+ }
+ return;
+
+cleanup_ret:
+ if (utask) {
+ utask->active_uprobe = NULL;
+ utask->state = UTASK_RUNNING;
+ }
+ if (u) {
+ put_uprobe(u);
+ set_instruction_pointer(regs, probept);
+ } else {
+ /*TODO Return SIGTRAP signal */
+ }
+}
+
+/*
+ * uprobe_bkpt_notifier gets called from interrupt context
+ * it gets a reference to the ppt and sets TIF_UPROBE flag,
+ */
+int uprobe_bkpt_notifier(struct pt_regs *regs)
+{
+ struct uprobe_task *utask;
+
+ if (!current->mm || !atomic_read(&current->mm->mm_uprobes_count))
+ /* task is currently not uprobed */
+ return 0;
+
+ utask = current->utask;
+ if (utask)
+ utask->state = UTASK_BP_HIT;
+ set_thread_flag(TIF_UPROBE);
+ return 1;
+}
+
+/*
+ * uprobe_post_notifier gets called in interrupt context.
+ * It completes the single step operation.
+ */
+int uprobe_post_notifier(struct pt_regs *regs)
+{
+ struct uprobe *uprobe;
+ struct uprobe_task *utask;
+
+ if (!current->mm || !current->utask || !current->utask->active_uprobe)
+ /* task is currently not uprobed */
+ return 0;
+
+ utask = current->utask;
+ uprobe = utask->active_uprobe;
+ set_thread_flag(TIF_UPROBE);
+ return 1;
+}

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