Re: [PATCH v2 3/4] mm: kmemleak: handle address stored in object based on its type

[Patrick Wang]

On 2022/6/6 23:01, Catalin Marinas wrote:
> On Fri, Jun 03, 2022 at 11:54:14AM +0800, Patrick Wang wrote:
> > Treat the address stored in object in different way according
> > to its type:
> >
> > - Only use kasan_reset_tag for virtual address
> > - Only update min_addr and max_addr for virtual address
> > - Convert physical address to virtual address in scan_object
> >
> > Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> > Signed-off-by: Patrick Wang <patrick.wang.shcn@xxxxxxxxx>
> > ---
> >   mm/kmemleak.c | 34 ++++++++++++++++++++++++----------
> >   1 file changed, 24 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> > index 218144392446..246a70b7218f 100644
> > --- a/mm/kmemleak.c
> > +++ b/mm/kmemleak.c
> > @@ -297,7 +297,9 @@ static void hex_dump_object(struct seq_file *seq,
> >   	warn_or_seq_printf(seq, "  hex dump (first %zu bytes):\n", len);
> >   	kasan_disable_current();
> >   	warn_or_seq_hex_dump(seq, DUMP_PREFIX_NONE, HEX_ROW_SIZE,
> > -			     HEX_GROUP_SIZE, kasan_reset_tag((void *)ptr), len, HEX_ASCII);
> > +			     HEX_GROUP_SIZE, object->flags & OBJECT_PHYS ? ptr :
> > +			     kasan_reset_tag((void *)ptr),
> > +			     len, HEX_ASCII);
> >   	kasan_enable_current();
> >   }
>
> This will go wrong since ptr is the actual physical address, it cannot
> be dereferenced. This should only be used on virtual pointers and this
> is the case already as we never print unreferenced objects from the phys
> tree. What we could do though is something like an early exit from this
> function (together with a comment that it doesn't support dumping such
> objects):
>
> 	if (WARN_ON_ONCE(object->flags & OBJECT_PHYS))
> 		return;

I also found this. Will do.

> >   
> > @@ -389,14 +391,15 @@ static struct kmemleak_object *lookup_object(unsigned long ptr, int alias,
> >   {
> >   	struct rb_node *rb = is_phys ? object_phys_tree_root.rb_node :
> >   			     object_tree_root.rb_node;
> > -	unsigned long untagged_ptr = (unsigned long)kasan_reset_tag((void *)ptr);
> > +	unsigned long untagged_ptr = is_phys ? ptr : (unsigned long)kasan_reset_tag((void *)ptr);
> >   
> >   	while (rb) {
> >   		struct kmemleak_object *object;
> >   		unsigned long untagged_objp;
> >   
> >   		object = rb_entry(rb, struct kmemleak_object, rb_node);
> > -		untagged_objp = (unsigned long)kasan_reset_tag((void *)object->pointer);
> > +		untagged_objp = is_phys ? object->pointer :
> > +				(unsigned long)kasan_reset_tag((void *)object->pointer);
> >   
> >   		if (untagged_ptr < untagged_objp)
> >   			rb = object->rb_node.rb_left;
>
> You could leave this unchanged. A phys pointer is already untagged, so
> it wouldn't make any difference.

Right, will do.

> > @@ -643,16 +646,19 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
> >   
> >   	raw_spin_lock_irqsave(&kmemleak_lock, flags);
> >   
> > -	untagged_ptr = (unsigned long)kasan_reset_tag((void *)ptr);
> > -	min_addr = min(min_addr, untagged_ptr);
> > -	max_addr = max(max_addr, untagged_ptr + size);
> > +	untagged_ptr = is_phys ? ptr : (unsigned long)kasan_reset_tag((void *)ptr);
>
> Same here.

Will do.

> > +	if (!is_phys) {
> > +		min_addr = min(min_addr, untagged_ptr);
> > +		max_addr = max(max_addr, untagged_ptr + size);
> > +	}
> >   	link = is_phys ? &object_phys_tree_root.rb_node :
> >   		&object_tree_root.rb_node;
> >   	rb_parent = NULL;
> >   	while (*link) {
> >   		rb_parent = *link;
> >   		parent = rb_entry(rb_parent, struct kmemleak_object, rb_node);
> > -		untagged_objp = (unsigned long)kasan_reset_tag((void *)parent->pointer);
> > +		untagged_objp = is_phys ? parent->pointer :
> > +				(unsigned long)kasan_reset_tag((void *)parent->pointer);
>
> And here.

Will do.

> >   		if (untagged_ptr + size <= untagged_objp)
> >   			link = &parent->rb_node.rb_left;
> >   		else if (untagged_objp + parent->size <= untagged_ptr)
> > @@ -1202,7 +1208,9 @@ static bool update_checksum(struct kmemleak_object *object)
> >   
> >   	kasan_disable_current();
> >   	kcsan_disable_current();
> > -	object->checksum = crc32(0, kasan_reset_tag((void *)object->pointer), object->size);
> > +	object->checksum = crc32(0, object->flags & OBJECT_PHYS ? (void *)object->pointer :
> > +				    kasan_reset_tag((void *)object->pointer),
> > +				    object->size);
>
> Luckily that's never called on a phys object, otherwise *object->pointer
> would segfault. As for hex_dump, just return early with a warning if
> that's the case.

Right, will do.

Thanks,
Patrick