[PATCH 0/2] uprobes: pre-filtering

[PATCH 0/2] uprobes: pre-filtering

[Oleg Nesterov]

Hello.

On top of preparations I sent a month ago. Srikar, you still didn't
review the last 2 patches. I assume you do not care so I am going to
add them without your ack.

Initially I was going to send more patches in this series. We can add
some optimizations to avoid the unnecessary register_for_each_vma() or
even consumer->filter() if there is a consumer with ->filter == NULL.
But lets do this later, lets discuss the functional change first.

Next steps:

	- teach handler_chain() to remove the unwanted breakpoints

	- if the above is not enough, implement UPROBE_FILTER_FORK

	- implement uprobe_apply(consumer, task, is_register) ?

Ole.

[PATCH 1/2] uprobes: Rationalize the usage of filter_chain()

[Oleg Nesterov]

filter_chain() was added into install_breakpoint/remove_breakpoint to
simplify the initial changes but this is sub-optimal.

This patch shifts the callsite to the callers, register_for_each_vma()
and uprobe_mmap(). This way:

- It will be easier to add the new arguments. This is the main reason,
  we can do more optimizations later.

- register_for_each_vma(is_register => true) can be optimized, we only
  need to consult the new consumer. The previous consumers were already
  asked when they called uprobe_register().

This patch also moves the MMF_HAS_UPROBES check from remove_breakpoint(),
this allows to avoid the potentionally costly filter_chain(). Note that
register_for_each_vma(is_register => false) doesn't really need to take
>consumer_rwsem, but I don't think it makes sense to optimize this and
introduce filter_chain_lockless().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 kernel/events/uprobes.c |   44 +++++++++++++++++++++-----------------------
 1 files changed, 21 insertions(+), 23 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 105ac0d..60b0a90 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -579,6 +579,11 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
 	return ret;
 }
 
+static inline bool consumer_filter(struct uprobe_consumer *uc)
+{
+	return true; /* TODO: !uc->filter || uc->filter(...) */
+}
+
 static bool filter_chain(struct uprobe *uprobe)
 {
 	struct uprobe_consumer *uc;
@@ -586,8 +591,7 @@ static bool filter_chain(struct uprobe *uprobe)
 
 	down_read(&uprobe->consumer_rwsem);
 	for (uc = uprobe->consumers; uc; uc = uc->next) {
-		/* TODO: ret = uc->filter(...) */
-		ret = true;
+		ret = consumer_filter(uc);
 		if (ret)
 			break;
 	}
@@ -603,15 +607,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 	bool first_uprobe;
 	int ret;
 
-	/*
-	 * If probe is being deleted, unregister thread could be done with
-	 * the vma-rmap-walk through. Adding a probe now can be fatal since
-	 * nobody will be able to cleanup. But in this case filter_chain()
-	 * must return false, all consumers have gone away.
-	 */
-	if (!filter_chain(uprobe))
-		return 0;
-
 	ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
 	if (ret)
 		return ret;
@@ -636,12 +631,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
 static int
 remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
 {
-	if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
-		return 0;
-
-	if (filter_chain(uprobe))
-		return 0;
-
 	set_bit(MMF_RECALC_UPROBES, &mm->flags);
 	return set_orig_insn(&uprobe->arch, mm, vaddr);
 }
@@ -781,10 +770,14 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 		    vaddr_to_offset(vma, info->vaddr) != uprobe->offset)
 			goto unlock;
 
-		if (is_register)
-			err = install_breakpoint(uprobe, mm, vma, info->vaddr);
-		else
-			err |= remove_breakpoint(uprobe, mm, info->vaddr);
+		if (is_register) {
+			/* consult only the "caller", new consumer. */
+			if (consumer_filter(uprobe->consumers))
+				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
+		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
+			if (!filter_chain(uprobe))
+				err |= remove_breakpoint(uprobe, mm, info->vaddr);
+		}
 
  unlock:
 		up_write(&mm->mmap_sem);
@@ -968,9 +961,14 @@ int uprobe_mmap(struct vm_area_struct *vma)
 
 	mutex_lock(uprobes_mmap_hash(inode));
 	build_probe_list(inode, vma, vma->vm_start, vma->vm_end, &tmp_list);
-
+	/*
+	 * We can race with uprobe_unregister(), this uprobe can be already
+	 * removed. But in this case filter_chain() must return false, all
+	 * consumers have gone away.
+	 */
 	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
-		if (!fatal_signal_pending(current)) {
+		if (!fatal_signal_pending(current) &&
+		    filter_chain(uprobe)) {
 			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
 			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
 		}
-- 
1.5.5.1

Re: [PATCH 1/2] uprobes: Rationalize the usage of filter_chain()

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2012-12-28 19:13:10]:

> filter_chain() was added into install_breakpoint/remove_breakpoint to
> simplify the initial changes but this is sub-optimal.
> 
> This patch shifts the callsite to the callers, register_for_each_vma()
> and uprobe_mmap(). This way:
> 
> - It will be easier to add the new arguments. This is the main reason,
>   we can do more optimizations later.
> 
> - register_for_each_vma(is_register => true) can be optimized, we only
>   need to consult the new consumer. The previous consumers were already
>   asked when they called uprobe_register().
> 
> This patch also moves the MMF_HAS_UPROBES check from remove_breakpoint(),
> this allows to avoid the potentionally costly filter_chain(). Note that
> register_for_each_vma(is_register => false) doesn't really need to take
> >consumer_rwsem, but I don't think it makes sense to optimize this and
> introduce filter_chain_lockless().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  kernel/events/uprobes.c |   44 +++++++++++++++++++++-----------------------
>  1 files changed, 21 insertions(+), 23 deletions(-)
> 
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 105ac0d..60b0a90 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -579,6 +579,11 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
>  	return ret;
>  }
> 
> +static inline bool consumer_filter(struct uprobe_consumer *uc)
> +{
> +	return true; /* TODO: !uc->filter || uc->filter(...) */
> +}
> +
>  static bool filter_chain(struct uprobe *uprobe)
>  {
>  	struct uprobe_consumer *uc;
> @@ -586,8 +591,7 @@ static bool filter_chain(struct uprobe *uprobe)
> 
>  	down_read(&uprobe->consumer_rwsem);
>  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> -		/* TODO: ret = uc->filter(...) */
> -		ret = true;
> +		ret = consumer_filter(uc);
>  		if (ret)
>  			break;
>  	}
> @@ -603,15 +607,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
>  	bool first_uprobe;
>  	int ret;
> 
> -	/*
> -	 * If probe is being deleted, unregister thread could be done with
> -	 * the vma-rmap-walk through. Adding a probe now can be fatal since
> -	 * nobody will be able to cleanup. But in this case filter_chain()
> -	 * must return false, all consumers have gone away.
> -	 */
> -	if (!filter_chain(uprobe))
> -		return 0;
> -
>  	ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
>  	if (ret)
>  		return ret;
> @@ -636,12 +631,6 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
>  static int
>  remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
>  {
> -	if (!test_bit(MMF_HAS_UPROBES, &mm->flags))
> -		return 0;
> -
> -	if (filter_chain(uprobe))
> -		return 0;
> -
>  	set_bit(MMF_RECALC_UPROBES, &mm->flags);
>  	return set_orig_insn(&uprobe->arch, mm, vaddr);
>  }
> @@ -781,10 +770,14 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
>  		    vaddr_to_offset(vma, info->vaddr) != uprobe->offset)
>  			goto unlock;
> 
> -		if (is_register)
> -			err = install_breakpoint(uprobe, mm, vma, info->vaddr);
> -		else
> -			err |= remove_breakpoint(uprobe, mm, info->vaddr);
> +		if (is_register) {
> +			/* consult only the "caller", new consumer. */
> +			if (consumer_filter(uprobe->consumers))
> +				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
> +		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
> +			if (!filter_chain(uprobe))
> +				err |= remove_breakpoint(uprobe, mm, info->vaddr);
> +		}
> 
>   unlock:
>  		up_write(&mm->mmap_sem);
> @@ -968,9 +961,14 @@ int uprobe_mmap(struct vm_area_struct *vma)
> 
>  	mutex_lock(uprobes_mmap_hash(inode));
>  	build_probe_list(inode, vma, vma->vm_start, vma->vm_end, &tmp_list);
> -
> +	/*
> +	 * We can race with uprobe_unregister(), this uprobe can be already
> +	 * removed. But in this case filter_chain() must return false, all
> +	 * consumers have gone away.
> +	 */
>  	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
> -		if (!fatal_signal_pending(current)) {
> +		if (!fatal_signal_pending(current) &&
> +		    filter_chain(uprobe)) {
>  			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
>  			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
>  		}
> -- 
> 1.5.5.1
> 

[PATCH 2/2] uprobes: Reintroduce uprobe_consumer->filter()

[Oleg Nesterov]

Finally add uprobe_consumer->filter() and change consumer_filter()
to actually call this method.

Note that ->filter() accepts mm_struct, not task_struct. Because:

	1. We do not have for_each_mm_user(mm, task).

	2. Even if we implement for_each_mm_user(), ->filter() can
	   use it itself.

	3. It is not clear who will actually need this interface to
	   do the "nontrivial" filtering.

Another argument is "enum uprobe_filter_ctx", consumer->filter() can
use it to figure out why/where it was called. For example, perhaps
we can add UPROBE_FILTER_PRE_REGISTER used by build_map_info() to
quickly "nack" the unwanted mm's. In this case consumer should know
that it is called under ->i_mmap_mutex.

See the previous discussion at http://marc.info/?t=135214229700002
Perhaps we should pass more arguments, vma/vaddr?

Note: this patch obviously can't help to filter out the child created
by fork(), this will be addressed later.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/uprobes.h |    9 +++++++++
 kernel/events/uprobes.c |   18 +++++++++++-------
 2 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 83742b9..c2df693 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -35,8 +35,17 @@ struct inode;
 # include <asm/uprobes.h>
 #endif
 
+enum uprobe_filter_ctx {
+	UPROBE_FILTER_REGISTER,
+	UPROBE_FILTER_UNREGISTER,
+	UPROBE_FILTER_MMAP,
+};
+
 struct uprobe_consumer {
 	int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
+	bool (*filter)(struct uprobe_consumer *self,
+				enum uprobe_filter_ctx ctx,
+				struct mm_struct *mm);
 
 	struct uprobe_consumer *next;
 };
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 60b0a90..e2ebb6f 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -579,19 +579,21 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
 	return ret;
 }
 
-static inline bool consumer_filter(struct uprobe_consumer *uc)
+static inline bool consumer_filter(struct uprobe_consumer *uc,
+				   enum uprobe_filter_ctx ctx, struct mm_struct *mm)
 {
-	return true; /* TODO: !uc->filter || uc->filter(...) */
+	return !uc->filter || uc->filter(uc, ctx, mm);
 }
 
-static bool filter_chain(struct uprobe *uprobe)
+static bool filter_chain(struct uprobe *uprobe,
+			 enum uprobe_filter_ctx ctx, struct mm_struct *mm)
 {
 	struct uprobe_consumer *uc;
 	bool ret = false;
 
 	down_read(&uprobe->consumer_rwsem);
 	for (uc = uprobe->consumers; uc; uc = uc->next) {
-		ret = consumer_filter(uc);
+		ret = consumer_filter(uc, ctx, mm);
 		if (ret)
 			break;
 	}
@@ -772,10 +774,12 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
 
 		if (is_register) {
 			/* consult only the "caller", new consumer. */
-			if (consumer_filter(uprobe->consumers))
+			if (consumer_filter(uprobe->consumers,
+					UPROBE_FILTER_REGISTER, mm))
 				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
 		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
-			if (!filter_chain(uprobe))
+			if (!filter_chain(uprobe,
+					UPROBE_FILTER_UNREGISTER, mm))
 				err |= remove_breakpoint(uprobe, mm, info->vaddr);
 		}
 
@@ -968,7 +972,7 @@ int uprobe_mmap(struct vm_area_struct *vma)
 	 */
 	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
 		if (!fatal_signal_pending(current) &&
-		    filter_chain(uprobe)) {
+		    filter_chain(uprobe, UPROBE_FILTER_MMAP, vma->vm_mm)) {
 			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
 			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
 		}
-- 
1.5.5.1

Re: [PATCH 2/2] uprobes: Reintroduce uprobe_consumer->filter()

[Srikar Dronamraju]

* Oleg Nesterov <oleg@redhat.com> [2012-12-28 19:13:14]:

> Finally add uprobe_consumer->filter() and change consumer_filter()
> to actually call this method.
> 
> Note that ->filter() accepts mm_struct, not task_struct. Because:
> 
> 	1. We do not have for_each_mm_user(mm, task).
> 
> 	2. Even if we implement for_each_mm_user(), ->filter() can
> 	   use it itself.
> 
> 	3. It is not clear who will actually need this interface to
> 	   do the "nontrivial" filtering.
> 
> Another argument is "enum uprobe_filter_ctx", consumer->filter() can
> use it to figure out why/where it was called. For example, perhaps
> we can add UPROBE_FILTER_PRE_REGISTER used by build_map_info() to
> quickly "nack" the unwanted mm's. In this case consumer should know
> that it is called under ->i_mmap_mutex.
> 
> See the previous discussion at http://marc.info/?t=135214229700002
> Perhaps we should pass more arguments, vma/vaddr?
> 
> Note: this patch obviously can't help to filter out the child created
> by fork(), this will be addressed later.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

> ---
>  include/linux/uprobes.h |    9 +++++++++
>  kernel/events/uprobes.c |   18 +++++++++++-------
>  2 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 83742b9..c2df693 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -35,8 +35,17 @@ struct inode;
>  # include <asm/uprobes.h>
>  #endif
> 
> +enum uprobe_filter_ctx {
> +	UPROBE_FILTER_REGISTER,
> +	UPROBE_FILTER_UNREGISTER,
> +	UPROBE_FILTER_MMAP,
> +};
> +
>  struct uprobe_consumer {
>  	int (*handler)(struct uprobe_consumer *self, struct pt_regs *regs);
> +	bool (*filter)(struct uprobe_consumer *self,
> +				enum uprobe_filter_ctx ctx,
> +				struct mm_struct *mm);
> 
>  	struct uprobe_consumer *next;
>  };
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 60b0a90..e2ebb6f 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -579,19 +579,21 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
>  	return ret;
>  }
> 
> -static inline bool consumer_filter(struct uprobe_consumer *uc)
> +static inline bool consumer_filter(struct uprobe_consumer *uc,
> +				   enum uprobe_filter_ctx ctx, struct mm_struct *mm)
>  {
> -	return true; /* TODO: !uc->filter || uc->filter(...) */
> +	return !uc->filter || uc->filter(uc, ctx, mm);
>  }
> 
> -static bool filter_chain(struct uprobe *uprobe)
> +static bool filter_chain(struct uprobe *uprobe,
> +			 enum uprobe_filter_ctx ctx, struct mm_struct *mm)
>  {
>  	struct uprobe_consumer *uc;
>  	bool ret = false;
> 
>  	down_read(&uprobe->consumer_rwsem);
>  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> -		ret = consumer_filter(uc);
> +		ret = consumer_filter(uc, ctx, mm);
>  		if (ret)
>  			break;
>  	}
> @@ -772,10 +774,12 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
> 
>  		if (is_register) {
>  			/* consult only the "caller", new consumer. */
> -			if (consumer_filter(uprobe->consumers))
> +			if (consumer_filter(uprobe->consumers,
> +					UPROBE_FILTER_REGISTER, mm))
>  				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
>  		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
> -			if (!filter_chain(uprobe))
> +			if (!filter_chain(uprobe,
> +					UPROBE_FILTER_UNREGISTER, mm))
>  				err |= remove_breakpoint(uprobe, mm, info->vaddr);
>  		}
> 
> @@ -968,7 +972,7 @@ int uprobe_mmap(struct vm_area_struct *vma)
>  	 */
>  	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
>  		if (!fatal_signal_pending(current) &&
> -		    filter_chain(uprobe)) {
> +		    filter_chain(uprobe, UPROBE_FILTER_MMAP, vma->vm_mm)) {
>  			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
>  			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
>  		}
> -- 
> 1.5.5.1
>