atomic_t variables are currently used to implement reference
counters with the following properties:
- counter is initialized to 1 using atomic_set()
- a resource is freed upon counter reaching zero
- once counter reaches zero, its further
increments aren't allowed
- counter schema uses basic atomic operations
(set, inc, inc_not_zero, dec_and_test, etc.)
Such atomic variables should be converted to a newly provided
refcount_t type and API that prevents accidental counter overflows
and underflows. This is important since overflows and underflows
can lead to use-after-free situation and be exploitable.
The variable uprobe.ref is used as pure reference counter.
Convert it to refcount_t and fix up the operations.
**Important note for maintainers:
Some functions from refcount_t API defined in lib/refcount.c
have different memory ordering guarantees than their atomic
counterparts.
The full comparison can be seen in
https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
in state to be merged to the documentation tree.
Normally the differences should not matter since refcount_t provides
enough guarantees to satisfy the refcounting use cases, but in
some rare cases it might matter.
Please double check that you don't have some undocumented
memory guarantees for this variable usage.
For the uprobe.ref it might make a difference
in following places:
- put_uprobe(): decrement in refcount_dec_and_test() only
provides RELEASE ordering and control dependency on success
vs. fully ordered atomic counterpart
Suggested-by: Kees Cook <[email protected]>
Reviewed-by: David Windsor <[email protected]>
Reviewed-by: Hans Liljestrand <[email protected]>
Signed-off-by: Elena Reshetova <[email protected]>
---
kernel/events/uprobes.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index ad415f7..750aece 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem;
struct uprobe {
struct rb_node rb_node; /* node in the rb tree */
- atomic_t ref;
+ refcount_t ref;
struct rw_semaphore register_rwsem;
struct rw_semaphore consumer_rwsem;
struct list_head pending_list;
@@ -561,13 +561,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
static struct uprobe *get_uprobe(struct uprobe *uprobe)
{
- atomic_inc(&uprobe->ref);
+ refcount_inc(&uprobe->ref);
return uprobe;
}
static void put_uprobe(struct uprobe *uprobe)
{
- if (atomic_dec_and_test(&uprobe->ref)) {
+ if (refcount_dec_and_test(&uprobe->ref)) {
/*
* If application munmap(exec_vma) before uprobe_unregister()
* gets called, we don't get a chance to remove uprobe from
@@ -658,7 +658,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
rb_link_node(&uprobe->rb_node, parent, p);
rb_insert_color(&uprobe->rb_node, &uprobes_tree);
/* get access + creation ref */
- atomic_set(&uprobe->ref, 2);
+ refcount_set(&uprobe->ref, 2);
return u;
}
--
2.7.4
[ Cc'ing Masami as he maintains uprobes (we need to add uprobes to
the MAINTAINERS file ]
-- Steve
On Wed, 16 Jan 2019 13:20:27 +0200
Elena Reshetova <[email protected]> wrote:
> atomic_t variables are currently used to implement reference
> counters with the following properties:
> - counter is initialized to 1 using atomic_set()
> - a resource is freed upon counter reaching zero
> - once counter reaches zero, its further
> increments aren't allowed
> - counter schema uses basic atomic operations
> (set, inc, inc_not_zero, dec_and_test, etc.)
>
> Such atomic variables should be converted to a newly provided
> refcount_t type and API that prevents accidental counter overflows
> and underflows. This is important since overflows and underflows
> can lead to use-after-free situation and be exploitable.
>
> The variable uprobe.ref is used as pure reference counter.
> Convert it to refcount_t and fix up the operations.
>
> **Important note for maintainers:
>
> Some functions from refcount_t API defined in lib/refcount.c
> have different memory ordering guarantees than their atomic
> counterparts.
> The full comparison can be seen in
> https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
> in state to be merged to the documentation tree.
> Normally the differences should not matter since refcount_t provides
> enough guarantees to satisfy the refcounting use cases, but in
> some rare cases it might matter.
> Please double check that you don't have some undocumented
> memory guarantees for this variable usage.
>
> For the uprobe.ref it might make a difference
> in following places:
> - put_uprobe(): decrement in refcount_dec_and_test() only
> provides RELEASE ordering and control dependency on success
> vs. fully ordered atomic counterpart
>
> Suggested-by: Kees Cook <[email protected]>
> Reviewed-by: David Windsor <[email protected]>
> Reviewed-by: Hans Liljestrand <[email protected]>
> Signed-off-by: Elena Reshetova <[email protected]>
> ---
> kernel/events/uprobes.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index ad415f7..750aece 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem;
>
> struct uprobe {
> struct rb_node rb_node; /* node in the rb tree */
> - atomic_t ref;
> + refcount_t ref;
> struct rw_semaphore register_rwsem;
> struct rw_semaphore consumer_rwsem;
> struct list_head pending_list;
> @@ -561,13 +561,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
>
> static struct uprobe *get_uprobe(struct uprobe *uprobe)
> {
> - atomic_inc(&uprobe->ref);
> + refcount_inc(&uprobe->ref);
> return uprobe;
> }
>
> static void put_uprobe(struct uprobe *uprobe)
> {
> - if (atomic_dec_and_test(&uprobe->ref)) {
> + if (refcount_dec_and_test(&uprobe->ref)) {
> /*
> * If application munmap(exec_vma) before uprobe_unregister()
> * gets called, we don't get a chance to remove uprobe from
> @@ -658,7 +658,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
> rb_link_node(&uprobe->rb_node, parent, p);
> rb_insert_color(&uprobe->rb_node, &uprobes_tree);
> /* get access + creation ref */
> - atomic_set(&uprobe->ref, 2);
> + refcount_set(&uprobe->ref, 2);
>
> return u;
> }
On Wed, 16 Jan 2019 08:44:52 -0500
Steven Rostedt <[email protected]> wrote:
>
> [ Cc'ing Masami as he maintains uprobes (we need to add uprobes to
> the MAINTAINERS file ]
Thanks Steve, I think it is maintained mainly by Srikar and Oleg.
Srikar, Oleg, could you update MAINTAINERS file to add UPROBES entry?
And ack this change?
Thank you,
>
> -- Steve
>
> On Wed, 16 Jan 2019 13:20:27 +0200
> Elena Reshetova <[email protected]> wrote:
>
> > atomic_t variables are currently used to implement reference
> > counters with the following properties:
> > - counter is initialized to 1 using atomic_set()
> > - a resource is freed upon counter reaching zero
> > - once counter reaches zero, its further
> > increments aren't allowed
> > - counter schema uses basic atomic operations
> > (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > Such atomic variables should be converted to a newly provided
> > refcount_t type and API that prevents accidental counter overflows
> > and underflows. This is important since overflows and underflows
> > can lead to use-after-free situation and be exploitable.
> >
> > The variable uprobe.ref is used as pure reference counter.
> > Convert it to refcount_t and fix up the operations.
> >
> > **Important note for maintainers:
> >
> > Some functions from refcount_t API defined in lib/refcount.c
> > have different memory ordering guarantees than their atomic
> > counterparts.
> > The full comparison can be seen in
> > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
> > in state to be merged to the documentation tree.
> > Normally the differences should not matter since refcount_t provides
> > enough guarantees to satisfy the refcounting use cases, but in
> > some rare cases it might matter.
> > Please double check that you don't have some undocumented
> > memory guarantees for this variable usage.
> >
> > For the uprobe.ref it might make a difference
> > in following places:
> > - put_uprobe(): decrement in refcount_dec_and_test() only
> > provides RELEASE ordering and control dependency on success
> > vs. fully ordered atomic counterpart
> >
> > Suggested-by: Kees Cook <[email protected]>
> > Reviewed-by: David Windsor <[email protected]>
> > Reviewed-by: Hans Liljestrand <[email protected]>
> > Signed-off-by: Elena Reshetova <[email protected]>
> > ---
> > kernel/events/uprobes.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> > index ad415f7..750aece 100644
> > --- a/kernel/events/uprobes.c
> > +++ b/kernel/events/uprobes.c
> > @@ -66,7 +66,7 @@ static struct percpu_rw_semaphore dup_mmap_sem;
> >
> > struct uprobe {
> > struct rb_node rb_node; /* node in the rb tree */
> > - atomic_t ref;
> > + refcount_t ref;
> > struct rw_semaphore register_rwsem;
> > struct rw_semaphore consumer_rwsem;
> > struct list_head pending_list;
> > @@ -561,13 +561,13 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
> >
> > static struct uprobe *get_uprobe(struct uprobe *uprobe)
> > {
> > - atomic_inc(&uprobe->ref);
> > + refcount_inc(&uprobe->ref);
> > return uprobe;
> > }
> >
> > static void put_uprobe(struct uprobe *uprobe)
> > {
> > - if (atomic_dec_and_test(&uprobe->ref)) {
> > + if (refcount_dec_and_test(&uprobe->ref)) {
> > /*
> > * If application munmap(exec_vma) before uprobe_unregister()
> > * gets called, we don't get a chance to remove uprobe from
> > @@ -658,7 +658,7 @@ static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
> > rb_link_node(&uprobe->rb_node, parent, p);
> > rb_insert_color(&uprobe->rb_node, &uprobes_tree);
> > /* get access + creation ref */
> > - atomic_set(&uprobe->ref, 2);
> > + refcount_set(&uprobe->ref, 2);
> >
> > return u;
> > }
>
--
Masami Hiramatsu <[email protected]>
> [ Cc'ing Masami as he maintains uprobes (we need to add uprobes to
> > the MAINTAINERS file ]
>
> Thanks Steve, I think it is maintained mainly by Srikar and Oleg.
> Srikar, Oleg, could you update MAINTAINERS file to add UPROBES entry?
> And ack this change?
Srikar, Oleg, could you please take a look on the change, if possible, it is
really a trivial one in this case.
Best Regards,
Elena.
On 01/31, Reshetova, Elena wrote:
>
> > [ Cc'ing Masami as he maintains uprobes (we need to add uprobes to
> > > the MAINTAINERS file ]
> >
> > Thanks Steve, I think it is maintained mainly by Srikar and Oleg.
> > Srikar, Oleg, could you update MAINTAINERS file to add UPROBES entry?
> > And ack this change?
>
> Srikar, Oleg, could you please take a look on the change, if possible, it is
> really a trivial one in this case.
this one https://lore.kernel.org/lkml/[email protected]/
I guess...
Yes, looks obviously correct, feel free to add my ACK,
Oleg.
* Elena Reshetova <[email protected]> [2019-01-16 13:20:27]:
> atomic_t variables are currently used to implement reference
> counters with the following properties:
> - counter is initialized to 1 using atomic_set()
> - a resource is freed upon counter reaching zero
> - once counter reaches zero, its further
> increments aren't allowed
> - counter schema uses basic atomic operations
> (set, inc, inc_not_zero, dec_and_test, etc.)
>
> Such atomic variables should be converted to a newly provided
> refcount_t type and API that prevents accidental counter overflows
> and underflows. This is important since overflows and underflows
> can lead to use-after-free situation and be exploitable.
>
> The variable uprobe.ref is used as pure reference counter.
> Convert it to refcount_t and fix up the operations.
>
> **Important note for maintainers:
>
> Some functions from refcount_t API defined in lib/refcount.c
> have different memory ordering guarantees than their atomic
> counterparts.
> The full comparison can be seen in
> https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
> in state to be merged to the documentation tree.
> Normally the differences should not matter since refcount_t provides
> enough guarantees to satisfy the refcounting use cases, but in
> some rare cases it might matter.
> Please double check that you don't have some undocumented
> memory guarantees for this variable usage.
>
> For the uprobe.ref it might make a difference
> in following places:
> - put_uprobe(): decrement in refcount_dec_and_test() only
> provides RELEASE ordering and control dependency on success
> vs. fully ordered atomic counterpart
>
> Suggested-by: Kees Cook <[email protected]>
> Reviewed-by: David Windsor <[email protected]>
> Reviewed-by: Hans Liljestrand <[email protected]>
> Signed-off-by: Elena Reshetova <[email protected]>
> ---
> kernel/events/uprobes.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
Looks good to me.
Reviewed-by: Srikar Dronamraju <[email protected]>
--
Thanks and Regards
Srikar Dronamraju
> * Elena Reshetova <[email protected]> [2019-01-16 13:20:27]:
>
> > atomic_t variables are currently used to implement reference
> > counters with the following properties:
> > - counter is initialized to 1 using atomic_set()
> > - a resource is freed upon counter reaching zero
> > - once counter reaches zero, its further
> > increments aren't allowed
> > - counter schema uses basic atomic operations
> > (set, inc, inc_not_zero, dec_and_test, etc.)
> >
> > Such atomic variables should be converted to a newly provided
> > refcount_t type and API that prevents accidental counter overflows
> > and underflows. This is important since overflows and underflows
> > can lead to use-after-free situation and be exploitable.
> >
> > The variable uprobe.ref is used as pure reference counter.
> > Convert it to refcount_t and fix up the operations.
> >
> > **Important note for maintainers:
> >
> > Some functions from refcount_t API defined in lib/refcount.c
> > have different memory ordering guarantees than their atomic
> > counterparts.
> > The full comparison can be seen in
> > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
> > in state to be merged to the documentation tree.
> > Normally the differences should not matter since refcount_t provides
> > enough guarantees to satisfy the refcounting use cases, but in
> > some rare cases it might matter.
> > Please double check that you don't have some undocumented
> > memory guarantees for this variable usage.
> >
> > For the uprobe.ref it might make a difference
> > in following places:
> > - put_uprobe(): decrement in refcount_dec_and_test() only
> > provides RELEASE ordering and control dependency on success
> > vs. fully ordered atomic counterpart
> >
> > Suggested-by: Kees Cook <[email protected]>
> > Reviewed-by: David Windsor <[email protected]>
> > Reviewed-by: Hans Liljestrand <[email protected]>
> > Signed-off-by: Elena Reshetova <[email protected]>
> > ---
> > kernel/events/uprobes.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Looks good to me.
>
> Reviewed-by: Srikar Dronamraju <[email protected]>
Thank you very much Srikar!
Would you be able to take this patch to integration?
Best Regards,
Elena.
On Sun, Feb 3, 2019 at 10:51 PM Reshetova, Elena
<[email protected]> wrote:
>
>
> > * Elena Reshetova <[email protected]> [2019-01-16 13:20:27]:
> >
> > > atomic_t variables are currently used to implement reference
> > > counters with the following properties:
> > > - counter is initialized to 1 using atomic_set()
> > > - a resource is freed upon counter reaching zero
> > > - once counter reaches zero, its further
> > > increments aren't allowed
> > > - counter schema uses basic atomic operations
> > > (set, inc, inc_not_zero, dec_and_test, etc.)
> > >
> > > Such atomic variables should be converted to a newly provided
> > > refcount_t type and API that prevents accidental counter overflows
> > > and underflows. This is important since overflows and underflows
> > > can lead to use-after-free situation and be exploitable.
> > >
> > > The variable uprobe.ref is used as pure reference counter.
> > > Convert it to refcount_t and fix up the operations.
> > >
> > > **Important note for maintainers:
> > >
> > > Some functions from refcount_t API defined in lib/refcount.c
> > > have different memory ordering guarantees than their atomic
> > > counterparts.
> > > The full comparison can be seen in
> > > https://lkml.org/lkml/2017/11/15/57 and it is hopefully soon
> > > in state to be merged to the documentation tree.
> > > Normally the differences should not matter since refcount_t provides
> > > enough guarantees to satisfy the refcounting use cases, but in
> > > some rare cases it might matter.
> > > Please double check that you don't have some undocumented
> > > memory guarantees for this variable usage.
> > >
> > > For the uprobe.ref it might make a difference
> > > in following places:
> > > - put_uprobe(): decrement in refcount_dec_and_test() only
> > > provides RELEASE ordering and control dependency on success
> > > vs. fully ordered atomic counterpart
> > >
> > > Suggested-by: Kees Cook <[email protected]>
> > > Reviewed-by: David Windsor <[email protected]>
> > > Reviewed-by: Hans Liljestrand <[email protected]>
> > > Signed-off-by: Elena Reshetova <[email protected]>
> > > ---
> > > kernel/events/uprobes.c | 8 ++++----
> > > 1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> >
> > Looks good to me.
> >
> > Reviewed-by: Srikar Dronamraju <[email protected]>
>
> Thank you very much Srikar!
> Would you be able to take this patch to integration?
Steve can you pick this up with Srikar's Reviewed-by?
--
Kees Cook
On Mon, 11 Feb 2019 12:21:32 -0800
Kees Cook <[email protected]> wrote:
> > > Looks good to me.
> > >
> > > Reviewed-by: Srikar Dronamraju <[email protected]>
> >
> > Thank you very much Srikar!
> > Would you be able to take this patch to integration?
>
> Steve can you pick this up with Srikar's Reviewed-by?
Yep. And I'll also add Oleg's acked-by. (Currently doing my "urgent"
patches now).
Thanks!
-- Steve
On Mon, 11 Feb 2019 15:27:25 -0500
Steven Rostedt <[email protected]> wrote:
> On Mon, 11 Feb 2019 12:21:32 -0800
> Kees Cook <[email protected]> wrote:
>
> > > > Looks good to me.
> > > >
> > > > Reviewed-by: Srikar Dronamraju <[email protected]>
> > >
> > > Thank you very much Srikar!
> > > Would you be able to take this patch to integration?
> >
> > Steve can you pick this up with Srikar's Reviewed-by?
>
> Yep. And I'll also add Oleg's acked-by. (Currently doing my "urgent"
> patches now).
>
Or is this something that can wait till the next merge window?
-- Steve
On Mon, Feb 11, 2019 at 12:28 PM Steven Rostedt <[email protected]> wrote:
>
> On Mon, 11 Feb 2019 15:27:25 -0500
> Steven Rostedt <[email protected]> wrote:
>
> > On Mon, 11 Feb 2019 12:21:32 -0800
> > Kees Cook <[email protected]> wrote:
> >
> > > > > Looks good to me.
> > > > >
> > > > > Reviewed-by: Srikar Dronamraju <[email protected]>
> > > >
> > > > Thank you very much Srikar!
> > > > Would you be able to take this patch to integration?
> > >
> > > Steve can you pick this up with Srikar's Reviewed-by?
> >
> > Yep. And I'll also add Oleg's acked-by. (Currently doing my "urgent"
> > patches now).
> >
>
> Or is this something that can wait till the next merge window?
I wouldn't classify the change as _urgent_, no. For "next merge
window" you mean v5.1, I assume? I think that'd be fine unless Elena
sees something I don't.
Thanks!
--
Kees Cook
On Mon, 11 Feb 2019 13:49:27 -0800
Kees Cook <[email protected]> wrote:
> On Mon, Feb 11, 2019 at 12:28 PM Steven Rostedt <[email protected]> wrote:
> >
> > On Mon, 11 Feb 2019 15:27:25 -0500
> > Steven Rostedt <[email protected]> wrote:
> >
> > > On Mon, 11 Feb 2019 12:21:32 -0800
> > > Kees Cook <[email protected]> wrote:
> > >
> > > > > > Looks good to me.
> > > > > >
> > > > > > Reviewed-by: Srikar Dronamraju <[email protected]>
> > > > >
> > > > > Thank you very much Srikar!
> > > > > Would you be able to take this patch to integration?
> > > >
> > > > Steve can you pick this up with Srikar's Reviewed-by?
> > >
> > > Yep. And I'll also add Oleg's acked-by. (Currently doing my "urgent"
> > > patches now).
> > >
> >
> > Or is this something that can wait till the next merge window?
>
> I wouldn't classify the change as _urgent_, no. For "next merge
> window" you mean v5.1, I assume? I think that'd be fine unless Elena
> sees something I don't.
OK, then I'll just place this in the "for-next" branch of mine. Still
need to test what I current have ;-)
-- Steve
On Mon, 11 Feb 2019 13:49:27 -0800
> Kees Cook <[email protected]> wrote:
>
> > On Mon, Feb 11, 2019 at 12:28 PM Steven Rostedt <[email protected]> wrote:
> > >
> > > On Mon, 11 Feb 2019 15:27:25 -0500
> > > Steven Rostedt <[email protected]> wrote:
> > >
> > > > On Mon, 11 Feb 2019 12:21:32 -0800
> > > > Kees Cook <[email protected]> wrote:
> > > >
> > > > > > > Looks good to me.
> > > > > > >
> > > > > > > Reviewed-by: Srikar Dronamraju <[email protected]>
> > > > > >
> > > > > > Thank you very much Srikar!
> > > > > > Would you be able to take this patch to integration?
> > > > >
> > > > > Steve can you pick this up with Srikar's Reviewed-by?
> > > >
> > > > Yep. And I'll also add Oleg's acked-by. (Currently doing my "urgent"
> > > > patches now).
> > > >
> > >
> > > Or is this something that can wait till the next merge window?
> >
> > I wouldn't classify the change as _urgent_, no. For "next merge
> > window" you mean v5.1, I assume? I think that'd be fine unless Elena
> > sees something I don't.
>
> OK, then I'll just place this in the "for-next" branch of mine. Still
> need to test what I current have ;-)
Sure, thank you very much! It is not any urgent stuff!
Best Regards,
Elena.