With HW tag-based kasan enable, We will get the warning
when we free object whose address starts with 0xFF.
It is because kmemleak rbtree stores tagged object and
this freeing object's tag does not match with rbtree object.
In the example below, kmemleak rbtree stores the tagged object in
the kmalloc(), and kfree() gets the pointer with 0xFF tag.
Call sequence:
ptr = kmalloc(size, GFP_KERNEL);
page = virt_to_page(ptr);
kfree(page_address(page));
ptr = kmalloc(size, GFP_KERNEL);
Call sequence like that may cause the warning as following:
1) Freeing unknown object:
In kfree(), we will get free unknown object warning in kmemleak_free().
Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in kfree() have
different tag.
2) Overlap existing:
When we allocate that object with the same hw-tag again, we will
find the overlap in the kmemleak rbtree and kmemleak thread will
be killed.
[ 116.685312] kmemleak: Freeing unknown object at 0xffff000003f88000
[ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-dirty #21
[ 116.687067] Hardware name: linux,dummy-virt (DT)
[ 116.687496] Call trace:
[ 116.687792] dump_backtrace+0x0/0x1ac
[ 116.688255] show_stack+0x1c/0x30
[ 116.688663] dump_stack_lvl+0x68/0x84
[ 116.689096] dump_stack+0x1c/0x38
[ 116.689499] kmemleak_free+0x6c/0x70
[ 116.689919] slab_free_freelist_hook+0x104/0x200
[ 116.690420] kmem_cache_free+0xa8/0x3d4
[ 116.690845] test_version_show+0x270/0x3a0
[ 116.691344] module_attr_show+0x28/0x40
[ 116.691789] sysfs_kf_seq_show+0xb0/0x130
[ 116.692245] kernfs_seq_show+0x30/0x40
[ 116.692678] seq_read_iter+0x1bc/0x4b0
[ 116.692678] seq_read_iter+0x1bc/0x4b0
[ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
[ 116.693586] generic_file_splice_read+0xd0/0x184
[ 116.694078] do_splice_to+0x90/0xe0
[ 116.694498] splice_direct_to_actor+0xb8/0x250
[ 116.694975] do_splice_direct+0x88/0xd4
[ 116.695409] do_sendfile+0x2b0/0x344
[ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
[ 116.696306] invoke_syscall+0x48/0x114
[ 116.696735] el0_svc_common.constprop.0+0x44/0xec
[ 116.697263] do_el0_svc+0x74/0x90
[ 116.697665] el0_svc+0x20/0x80
[ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
[ 116.698695] el0t_64_sync+0x1ac/0x1b0
...
[ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into the object search tree (overlaps existing)
[ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-dirty #21
[ 117.521827] Hardware name: linux,dummy-virt (DT)
[ 117.522287] Call trace:
[ 117.522586] dump_backtrace+0x0/0x1ac
[ 117.523053] show_stack+0x1c/0x30
[ 117.523578] dump_stack_lvl+0x68/0x84
[ 117.524039] dump_stack+0x1c/0x38
[ 117.524472] create_object.isra.0+0x2d8/0x2fc
[ 117.524975] kmemleak_alloc+0x34/0x40
[ 117.525416] kmem_cache_alloc+0x23c/0x2f0
[ 117.525914] test_version_show+0x1fc/0x3a0
[ 117.526379] module_attr_show+0x28/0x40
[ 117.526827] sysfs_kf_seq_show+0xb0/0x130
[ 117.527363] kernfs_seq_show+0x30/0x40
[ 117.527848] seq_read_iter+0x1bc/0x4b0
[ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
[ 117.528809] generic_file_splice_read+0xd0/0x184
[ 117.529316] do_splice_to+0x90/0xe0
[ 117.529734] splice_direct_to_actor+0xb8/0x250
[ 117.530227] do_splice_direct+0x88/0xd4
[ 117.530686] do_sendfile+0x2b0/0x344
[ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
[ 117.531673] invoke_syscall+0x48/0x114
[ 117.532111] el0_svc_common.constprop.0+0x44/0xec
[ 117.532621] do_el0_svc+0x74/0x90
[ 117.533048] el0_svc+0x20/0x80
[ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
[ 117.533950] el0t_64_sync+0x1ac/0x1b0
[ 117.534625] kmemleak: Kernel memory leak detector disabled
[ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
[ 117.535761] kmemleak: comm "cat", pid 177, jiffies 4294921177
[ 117.536339] kmemleak: min_count = 1
[ 117.536718] kmemleak: count = 0
[ 117.537068] kmemleak: flags = 0x1
[ 117.537429] kmemleak: checksum = 0
[ 117.537806] kmemleak: backtrace:
[ 117.538211] kmem_cache_alloc+0x23c/0x2f0
[ 117.538924] test_version_show+0x1fc/0x3a0
[ 117.539393] module_attr_show+0x28/0x40
[ 117.539844] sysfs_kf_seq_show+0xb0/0x130
[ 117.540304] kernfs_seq_show+0x30/0x40
[ 117.540750] seq_read_iter+0x1bc/0x4b0
[ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
[ 117.541687] generic_file_splice_read+0xd0/0x184
[ 117.542182] do_splice_to+0x90/0xe0
[ 117.542611] splice_direct_to_actor+0xb8/0x250
[ 117.543097] do_splice_direct+0x88/0xd4
[ 117.543544] do_sendfile+0x2b0/0x344
[ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
[ 117.544471] invoke_syscall+0x48/0x114
[ 117.544917] el0_svc_common.constprop.0+0x44/0xec
[ 117.545416] do_el0_svc+0x74/0x90
[ 117.554100] kmemleak: Automatic memory scanning thread ended
Signed-off-by: Kuan-Ying Lee <[email protected]>
---
mm/kmemleak.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index b57383c17cf6..fa12e2e08cdc 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -381,15 +381,20 @@ static void dump_object_info(struct kmemleak_object *object)
static struct kmemleak_object *lookup_object(unsigned long ptr, int alias)
{
struct rb_node *rb = object_tree_root.rb_node;
+ unsigned long untagged_ptr = (unsigned long)kasan_reset_tag((void *)ptr);
while (rb) {
struct kmemleak_object *object =
rb_entry(rb, struct kmemleak_object, rb_node);
- if (ptr < object->pointer)
+ unsigned long untagged_objp;
+
+ untagged_objp = (unsigned long)kasan_reset_tag((void *)object->pointer);
+
+ if (untagged_ptr < untagged_objp)
rb = object->rb_node.rb_left;
- else if (object->pointer + object->size <= ptr)
+ else if (untagged_objp + object->size <= untagged_ptr)
rb = object->rb_node.rb_right;
- else if (object->pointer == ptr || alias)
+ else if (untagged_objp == untagged_ptr || alias)
return object;
else {
kmemleak_warn("Found object by alias at 0x%08lx\n",
@@ -576,6 +581,7 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
struct kmemleak_object *object, *parent;
struct rb_node **link, *rb_parent;
unsigned long untagged_ptr;
+ unsigned long untagged_objp;
object = mem_pool_alloc(gfp);
if (!object) {
@@ -629,9 +635,10 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size,
while (*link) {
rb_parent = *link;
parent = rb_entry(rb_parent, struct kmemleak_object, rb_node);
- if (ptr + size <= parent->pointer)
+ untagged_objp = (unsigned long)kasan_reset_tag((void *)parent->pointer);
+ if (untagged_ptr + size <= untagged_objp)
link = &parent->rb_node.rb_left;
- else if (parent->pointer + parent->size <= ptr)
+ else if (untagged_objp + parent->size <= untagged_ptr)
link = &parent->rb_node.rb_right;
else {
kmemleak_stop("Cannot insert 0x%lx into the object search tree (overlaps existing)\n",
--
2.18.0
+Cc kasan group
On Thu, 2021-11-18 at 13:44 +0800, Kuan-Ying Lee wrote:
> With HW tag-based kasan enable, We will get the warning
> when we free object whose address starts with 0xFF.
>
> It is because kmemleak rbtree stores tagged object and
> this freeing object's tag does not match with rbtree object.
>
> In the example below, kmemleak rbtree stores the tagged object in
> the kmalloc(), and kfree() gets the pointer with 0xFF tag.
>
> Call sequence:
> ptr = kmalloc(size, GFP_KERNEL);
> page = virt_to_page(ptr);
> kfree(page_address(page));
> ptr = kmalloc(size, GFP_KERNEL);
>
> Call sequence like that may cause the warning as following:
> 1) Freeing unknown object:
> In kfree(), we will get free unknown object warning in
> kmemleak_free().
> Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in kfree()
> have
> different tag.
>
> 2) Overlap existing:
> When we allocate that object with the same hw-tag again, we will
> find the overlap in the kmemleak rbtree and kmemleak thread will
> be killed.
>
> [ 116.685312] kmemleak: Freeing unknown object at 0xffff000003f88000
> [ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-dirty
> #21
> [ 116.687067] Hardware name: linux,dummy-virt (DT)
> [ 116.687496] Call trace:
> [ 116.687792] dump_backtrace+0x0/0x1ac
> [ 116.688255] show_stack+0x1c/0x30
> [ 116.688663] dump_stack_lvl+0x68/0x84
> [ 116.689096] dump_stack+0x1c/0x38
> [ 116.689499] kmemleak_free+0x6c/0x70
> [ 116.689919] slab_free_freelist_hook+0x104/0x200
> [ 116.690420] kmem_cache_free+0xa8/0x3d4
> [ 116.690845] test_version_show+0x270/0x3a0
> [ 116.691344] module_attr_show+0x28/0x40
> [ 116.691789] sysfs_kf_seq_show+0xb0/0x130
> [ 116.692245] kernfs_seq_show+0x30/0x40
> [ 116.692678] seq_read_iter+0x1bc/0x4b0
> [ 116.692678] seq_read_iter+0x1bc/0x4b0
> [ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
> [ 116.693586] generic_file_splice_read+0xd0/0x184
> [ 116.694078] do_splice_to+0x90/0xe0
> [ 116.694498] splice_direct_to_actor+0xb8/0x250
> [ 116.694975] do_splice_direct+0x88/0xd4
> [ 116.695409] do_sendfile+0x2b0/0x344
> [ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
> [ 116.696306] invoke_syscall+0x48/0x114
> [ 116.696735] el0_svc_common.constprop.0+0x44/0xec
> [ 116.697263] do_el0_svc+0x74/0x90
> [ 116.697665] el0_svc+0x20/0x80
> [ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
> [ 116.698695] el0t_64_sync+0x1ac/0x1b0
> ...
> [ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into the
> object search tree (overlaps existing)
> [ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-dirty
> #21
> [ 117.521827] Hardware name: linux,dummy-virt (DT)
> [ 117.522287] Call trace:
> [ 117.522586] dump_backtrace+0x0/0x1ac
> [ 117.523053] show_stack+0x1c/0x30
> [ 117.523578] dump_stack_lvl+0x68/0x84
> [ 117.524039] dump_stack+0x1c/0x38
> [ 117.524472] create_object.isra.0+0x2d8/0x2fc
> [ 117.524975] kmemleak_alloc+0x34/0x40
> [ 117.525416] kmem_cache_alloc+0x23c/0x2f0
> [ 117.525914] test_version_show+0x1fc/0x3a0
> [ 117.526379] module_attr_show+0x28/0x40
> [ 117.526827] sysfs_kf_seq_show+0xb0/0x130
> [ 117.527363] kernfs_seq_show+0x30/0x40
> [ 117.527848] seq_read_iter+0x1bc/0x4b0
> [ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
> [ 117.528809] generic_file_splice_read+0xd0/0x184
> [ 117.529316] do_splice_to+0x90/0xe0
> [ 117.529734] splice_direct_to_actor+0xb8/0x250
> [ 117.530227] do_splice_direct+0x88/0xd4
> [ 117.530686] do_sendfile+0x2b0/0x344
> [ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
> [ 117.531673] invoke_syscall+0x48/0x114
> [ 117.532111] el0_svc_common.constprop.0+0x44/0xec
> [ 117.532621] do_el0_svc+0x74/0x90
> [ 117.533048] el0_svc+0x20/0x80
> [ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
> [ 117.533950] el0t_64_sync+0x1ac/0x1b0
> [ 117.534625] kmemleak: Kernel memory leak detector disabled
> [ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
> [ 117.535761] kmemleak: comm "cat", pid 177, jiffies 4294921177
> [ 117.536339] kmemleak: min_count = 1
> [ 117.536718] kmemleak: count = 0
> [ 117.537068] kmemleak: flags = 0x1
> [ 117.537429] kmemleak: checksum = 0
> [ 117.537806] kmemleak: backtrace:
> [ 117.538211] kmem_cache_alloc+0x23c/0x2f0
> [ 117.538924] test_version_show+0x1fc/0x3a0
> [ 117.539393] module_attr_show+0x28/0x40
> [ 117.539844] sysfs_kf_seq_show+0xb0/0x130
> [ 117.540304] kernfs_seq_show+0x30/0x40
> [ 117.540750] seq_read_iter+0x1bc/0x4b0
> [ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
> [ 117.541687] generic_file_splice_read+0xd0/0x184
> [ 117.542182] do_splice_to+0x90/0xe0
> [ 117.542611] splice_direct_to_actor+0xb8/0x250
> [ 117.543097] do_splice_direct+0x88/0xd4
> [ 117.543544] do_sendfile+0x2b0/0x344
> [ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
> [ 117.544471] invoke_syscall+0x48/0x114
> [ 117.544917] el0_svc_common.constprop.0+0x44/0xec
> [ 117.545416] do_el0_svc+0x74/0x90
> [ 117.554100] kmemleak: Automatic memory scanning thread ended
>
> Signed-off-by: Kuan-Ying Lee <[email protected]>
> ---
> mm/kmemleak.c | 17 ++++++++++++-----
> 1 file changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index b57383c17cf6..fa12e2e08cdc 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -381,15 +381,20 @@ static void dump_object_info(struct
> kmemleak_object *object)
> static struct kmemleak_object *lookup_object(unsigned long ptr, int
> alias)
> {
> struct rb_node *rb = object_tree_root.rb_node;
> + unsigned long untagged_ptr = (unsigned
> long)kasan_reset_tag((void *)ptr);
>
> while (rb) {
> struct kmemleak_object *object =
> rb_entry(rb, struct kmemleak_object, rb_node);
> - if (ptr < object->pointer)
> + unsigned long untagged_objp;
> +
> + untagged_objp = (unsigned long)kasan_reset_tag((void
> *)object->pointer);
> +
> + if (untagged_ptr < untagged_objp)
> rb = object->rb_node.rb_left;
> - else if (object->pointer + object->size <= ptr)
> + else if (untagged_objp + object->size <= untagged_ptr)
> rb = object->rb_node.rb_right;
> - else if (object->pointer == ptr || alias)
> + else if (untagged_objp == untagged_ptr || alias)
> return object;
> else {
> kmemleak_warn("Found object by alias at
> 0x%08lx\n",
> @@ -576,6 +581,7 @@ static struct kmemleak_object
> *create_object(unsigned long ptr, size_t size,
> struct kmemleak_object *object, *parent;
> struct rb_node **link, *rb_parent;
> unsigned long untagged_ptr;
> + unsigned long untagged_objp;
>
> object = mem_pool_alloc(gfp);
> if (!object) {
> @@ -629,9 +635,10 @@ static struct kmemleak_object
> *create_object(unsigned long ptr, size_t size,
> while (*link) {
> rb_parent = *link;
> parent = rb_entry(rb_parent, struct kmemleak_object,
> rb_node);
> - if (ptr + size <= parent->pointer)
> + untagged_objp = (unsigned long)kasan_reset_tag((void
> *)parent->pointer);
> + if (untagged_ptr + size <= untagged_objp)
> link = &parent->rb_node.rb_left;
> - else if (parent->pointer + parent->size <= ptr)
> + else if (untagged_objp + parent->size <= untagged_ptr)
> link = &parent->rb_node.rb_right;
> else {
> kmemleak_stop("Cannot insert 0x%lx into the
> object search tree (overlaps existing)\n",
> --
> 2.18.0
>
On Thu, Nov 18, 2021 at 10:20 AM Kuan-Ying Lee
<[email protected]> wrote:
>
> +Cc kasan group
>
> On Thu, 2021-11-18 at 13:44 +0800, Kuan-Ying Lee wrote:
> > With HW tag-based kasan enable, We will get the warning
> > when we free object whose address starts with 0xFF.
> >
> > It is because kmemleak rbtree stores tagged object and
> > this freeing object's tag does not match with rbtree object.
> >
> > In the example below, kmemleak rbtree stores the tagged object in
> > the kmalloc(), and kfree() gets the pointer with 0xFF tag.
> >
> > Call sequence:
> > ptr = kmalloc(size, GFP_KERNEL);
> > page = virt_to_page(ptr);
> > kfree(page_address(page));
> > ptr = kmalloc(size, GFP_KERNEL);
How is this call sequence valid? page_address returns the address of
the start of the page, while kmalloced object could have been located
in the middle of it.
> >
> > Call sequence like that may cause the warning as following:
> > 1) Freeing unknown object:
> > In kfree(), we will get free unknown object warning in
> > kmemleak_free().
> > Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in kfree()
> > have
> > different tag.
> >
> > 2) Overlap existing:
> > When we allocate that object with the same hw-tag again, we will
> > find the overlap in the kmemleak rbtree and kmemleak thread will
> > be killed.
> >
> > [ 116.685312] kmemleak: Freeing unknown object at 0xffff000003f88000
> > [ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-dirty
> > #21
> > [ 116.687067] Hardware name: linux,dummy-virt (DT)
> > [ 116.687496] Call trace:
> > [ 116.687792] dump_backtrace+0x0/0x1ac
> > [ 116.688255] show_stack+0x1c/0x30
> > [ 116.688663] dump_stack_lvl+0x68/0x84
> > [ 116.689096] dump_stack+0x1c/0x38
> > [ 116.689499] kmemleak_free+0x6c/0x70
> > [ 116.689919] slab_free_freelist_hook+0x104/0x200
> > [ 116.690420] kmem_cache_free+0xa8/0x3d4
> > [ 116.690845] test_version_show+0x270/0x3a0
> > [ 116.691344] module_attr_show+0x28/0x40
> > [ 116.691789] sysfs_kf_seq_show+0xb0/0x130
> > [ 116.692245] kernfs_seq_show+0x30/0x40
> > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > [ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
> > [ 116.693586] generic_file_splice_read+0xd0/0x184
> > [ 116.694078] do_splice_to+0x90/0xe0
> > [ 116.694498] splice_direct_to_actor+0xb8/0x250
> > [ 116.694975] do_splice_direct+0x88/0xd4
> > [ 116.695409] do_sendfile+0x2b0/0x344
> > [ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
> > [ 116.696306] invoke_syscall+0x48/0x114
> > [ 116.696735] el0_svc_common.constprop.0+0x44/0xec
> > [ 116.697263] do_el0_svc+0x74/0x90
> > [ 116.697665] el0_svc+0x20/0x80
> > [ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
> > [ 116.698695] el0t_64_sync+0x1ac/0x1b0
> > ...
> > [ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into the
> > object search tree (overlaps existing)
> > [ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-dirty
> > #21
> > [ 117.521827] Hardware name: linux,dummy-virt (DT)
> > [ 117.522287] Call trace:
> > [ 117.522586] dump_backtrace+0x0/0x1ac
> > [ 117.523053] show_stack+0x1c/0x30
> > [ 117.523578] dump_stack_lvl+0x68/0x84
> > [ 117.524039] dump_stack+0x1c/0x38
> > [ 117.524472] create_object.isra.0+0x2d8/0x2fc
> > [ 117.524975] kmemleak_alloc+0x34/0x40
> > [ 117.525416] kmem_cache_alloc+0x23c/0x2f0
> > [ 117.525914] test_version_show+0x1fc/0x3a0
> > [ 117.526379] module_attr_show+0x28/0x40
> > [ 117.526827] sysfs_kf_seq_show+0xb0/0x130
> > [ 117.527363] kernfs_seq_show+0x30/0x40
> > [ 117.527848] seq_read_iter+0x1bc/0x4b0
> > [ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
> > [ 117.528809] generic_file_splice_read+0xd0/0x184
> > [ 117.529316] do_splice_to+0x90/0xe0
> > [ 117.529734] splice_direct_to_actor+0xb8/0x250
> > [ 117.530227] do_splice_direct+0x88/0xd4
> > [ 117.530686] do_sendfile+0x2b0/0x344
> > [ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
> > [ 117.531673] invoke_syscall+0x48/0x114
> > [ 117.532111] el0_svc_common.constprop.0+0x44/0xec
> > [ 117.532621] do_el0_svc+0x74/0x90
> > [ 117.533048] el0_svc+0x20/0x80
> > [ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
> > [ 117.533950] el0t_64_sync+0x1ac/0x1b0
> > [ 117.534625] kmemleak: Kernel memory leak detector disabled
> > [ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
> > [ 117.535761] kmemleak: comm "cat", pid 177, jiffies 4294921177
> > [ 117.536339] kmemleak: min_count = 1
> > [ 117.536718] kmemleak: count = 0
> > [ 117.537068] kmemleak: flags = 0x1
> > [ 117.537429] kmemleak: checksum = 0
> > [ 117.537806] kmemleak: backtrace:
> > [ 117.538211] kmem_cache_alloc+0x23c/0x2f0
> > [ 117.538924] test_version_show+0x1fc/0x3a0
> > [ 117.539393] module_attr_show+0x28/0x40
> > [ 117.539844] sysfs_kf_seq_show+0xb0/0x130
> > [ 117.540304] kernfs_seq_show+0x30/0x40
> > [ 117.540750] seq_read_iter+0x1bc/0x4b0
> > [ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
> > [ 117.541687] generic_file_splice_read+0xd0/0x184
> > [ 117.542182] do_splice_to+0x90/0xe0
> > [ 117.542611] splice_direct_to_actor+0xb8/0x250
> > [ 117.543097] do_splice_direct+0x88/0xd4
> > [ 117.543544] do_sendfile+0x2b0/0x344
> > [ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
> > [ 117.544471] invoke_syscall+0x48/0x114
> > [ 117.544917] el0_svc_common.constprop.0+0x44/0xec
> > [ 117.545416] do_el0_svc+0x74/0x90
> > [ 117.554100] kmemleak: Automatic memory scanning thread ended
> >
> > Signed-off-by: Kuan-Ying Lee <[email protected]>
> > ---
> > mm/kmemleak.c | 17 ++++++++++++-----
> > 1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> > index b57383c17cf6..fa12e2e08cdc 100644
> > --- a/mm/kmemleak.c
> > +++ b/mm/kmemleak.c
> > @@ -381,15 +381,20 @@ static void dump_object_info(struct
> > kmemleak_object *object)
> > static struct kmemleak_object *lookup_object(unsigned long ptr, int
> > alias)
> > {
> > struct rb_node *rb = object_tree_root.rb_node;
> > + unsigned long untagged_ptr = (unsigned
> > long)kasan_reset_tag((void *)ptr);
> >
> > while (rb) {
> > struct kmemleak_object *object =
> > rb_entry(rb, struct kmemleak_object, rb_node);
> > - if (ptr < object->pointer)
> > + unsigned long untagged_objp;
> > +
> > + untagged_objp = (unsigned long)kasan_reset_tag((void
> > *)object->pointer);
> > +
> > + if (untagged_ptr < untagged_objp)
> > rb = object->rb_node.rb_left;
> > - else if (object->pointer + object->size <= ptr)
> > + else if (untagged_objp + object->size <= untagged_ptr)
> > rb = object->rb_node.rb_right;
> > - else if (object->pointer == ptr || alias)
> > + else if (untagged_objp == untagged_ptr || alias)
> > return object;
> > else {
> > kmemleak_warn("Found object by alias at
> > 0x%08lx\n",
> > @@ -576,6 +581,7 @@ static struct kmemleak_object
> > *create_object(unsigned long ptr, size_t size,
> > struct kmemleak_object *object, *parent;
> > struct rb_node **link, *rb_parent;
> > unsigned long untagged_ptr;
> > + unsigned long untagged_objp;
> >
> > object = mem_pool_alloc(gfp);
> > if (!object) {
> > @@ -629,9 +635,10 @@ static struct kmemleak_object
> > *create_object(unsigned long ptr, size_t size,
> > while (*link) {
> > rb_parent = *link;
> > parent = rb_entry(rb_parent, struct kmemleak_object,
> > rb_node);
> > - if (ptr + size <= parent->pointer)
> > + untagged_objp = (unsigned long)kasan_reset_tag((void
> > *)parent->pointer);
> > + if (untagged_ptr + size <= untagged_objp)
> > link = &parent->rb_node.rb_left;
> > - else if (parent->pointer + parent->size <= ptr)
> > + else if (untagged_objp + parent->size <= untagged_ptr)
> > link = &parent->rb_node.rb_right;
> > else {
> > kmemleak_stop("Cannot insert 0x%lx into the
> > object search tree (overlaps existing)\n",
> > --
> > 2.18.0
> >
>
> --
> You received this message because you are subscribed to the Google Groups "kasan-dev" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
> To view this discussion on the web visit https://groups.google.com/d/msgid/kasan-dev/754511d9a0368065768cc3ad8037184d62c3fbd1.camel%40mediatek.com.
On Fri, 2021-11-19 at 22:15 +0800, Andrey Konovalov wrote:
> On Thu, Nov 18, 2021 at 10:20 AM Kuan-Ying Lee
> <[email protected]> wrote:
> >
> > +Cc kasan group
> >
> > On Thu, 2021-11-18 at 13:44 +0800, Kuan-Ying Lee wrote:
> > > With HW tag-based kasan enable, We will get the warning
> > > when we free object whose address starts with 0xFF.
> > >
> > > It is because kmemleak rbtree stores tagged object and
> > > this freeing object's tag does not match with rbtree object.
> > >
> > > In the example below, kmemleak rbtree stores the tagged object in
> > > the kmalloc(), and kfree() gets the pointer with 0xFF tag.
> > >
> > > Call sequence:
> > > ptr = kmalloc(size, GFP_KERNEL);
> > > page = virt_to_page(ptr);
> > > kfree(page_address(page));
> > > ptr = kmalloc(size, GFP_KERNEL);
>
> How is this call sequence valid? page_address returns the address of
> the start of the page, while kmalloced object could have been located
> in the middle of it.
Thanks for pointing out. I miss the offset.
It should be listed as below.
ptr = kmalloc(size, GFP_KERNEL);
page = virt_to_page(ptr);
offset = offset_in_page(ptr);
kfree(page_address(page) + offset);
ptr = kmalloc(size, GFP_KERNEL);
>
> > >
> > > Call sequence like that may cause the warning as following:
> > > 1) Freeing unknown object:
> > > In kfree(), we will get free unknown object warning in
> > > kmemleak_free().
> > > Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in
> > > kfree()
> > > have
> > > different tag.
> > >
> > > 2) Overlap existing:
> > > When we allocate that object with the same hw-tag again, we will
> > > find the overlap in the kmemleak rbtree and kmemleak thread will
> > > be killed.
> > >
> > > [ 116.685312] kmemleak: Freeing unknown object at
> > > 0xffff000003f88000
> > > [ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-
> > > dirty
> > > #21
> > > [ 116.687067] Hardware name: linux,dummy-virt (DT)
> > > [ 116.687496] Call trace:
> > > [ 116.687792] dump_backtrace+0x0/0x1ac
> > > [ 116.688255] show_stack+0x1c/0x30
> > > [ 116.688663] dump_stack_lvl+0x68/0x84
> > > [ 116.689096] dump_stack+0x1c/0x38
> > > [ 116.689499] kmemleak_free+0x6c/0x70
> > > [ 116.689919] slab_free_freelist_hook+0x104/0x200
> > > [ 116.690420] kmem_cache_free+0xa8/0x3d4
> > > [ 116.690845] test_version_show+0x270/0x3a0
> > > [ 116.691344] module_attr_show+0x28/0x40
> > > [ 116.691789] sysfs_kf_seq_show+0xb0/0x130
> > > [ 116.692245] kernfs_seq_show+0x30/0x40
> > > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > > [ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
> > > [ 116.693586] generic_file_splice_read+0xd0/0x184
> > > [ 116.694078] do_splice_to+0x90/0xe0
> > > [ 116.694498] splice_direct_to_actor+0xb8/0x250
> > > [ 116.694975] do_splice_direct+0x88/0xd4
> > > [ 116.695409] do_sendfile+0x2b0/0x344
> > > [ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
> > > [ 116.696306] invoke_syscall+0x48/0x114
> > > [ 116.696735] el0_svc_common.constprop.0+0x44/0xec
> > > [ 116.697263] do_el0_svc+0x74/0x90
> > > [ 116.697665] el0_svc+0x20/0x80
> > > [ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
> > > [ 116.698695] el0t_64_sync+0x1ac/0x1b0
> > > ...
> > > [ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into
> > > the
> > > object search tree (overlaps existing)
> > > [ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-
> > > dirty
> > > #21
> > > [ 117.521827] Hardware name: linux,dummy-virt (DT)
> > > [ 117.522287] Call trace:
> > > [ 117.522586] dump_backtrace+0x0/0x1ac
> > > [ 117.523053] show_stack+0x1c/0x30
> > > [ 117.523578] dump_stack_lvl+0x68/0x84
> > > [ 117.524039] dump_stack+0x1c/0x38
> > > [ 117.524472] create_object.isra.0+0x2d8/0x2fc
> > > [ 117.524975] kmemleak_alloc+0x34/0x40
> > > [ 117.525416] kmem_cache_alloc+0x23c/0x2f0
> > > [ 117.525914] test_version_show+0x1fc/0x3a0
> > > [ 117.526379] module_attr_show+0x28/0x40
> > > [ 117.526827] sysfs_kf_seq_show+0xb0/0x130
> > > [ 117.527363] kernfs_seq_show+0x30/0x40
> > > [ 117.527848] seq_read_iter+0x1bc/0x4b0
> > > [ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
> > > [ 117.528809] generic_file_splice_read+0xd0/0x184
> > > [ 117.529316] do_splice_to+0x90/0xe0
> > > [ 117.529734] splice_direct_to_actor+0xb8/0x250
> > > [ 117.530227] do_splice_direct+0x88/0xd4
> > > [ 117.530686] do_sendfile+0x2b0/0x344
> > > [ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
> > > [ 117.531673] invoke_syscall+0x48/0x114
> > > [ 117.532111] el0_svc_common.constprop.0+0x44/0xec
> > > [ 117.532621] do_el0_svc+0x74/0x90
> > > [ 117.533048] el0_svc+0x20/0x80
> > > [ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
> > > [ 117.533950] el0t_64_sync+0x1ac/0x1b0
> > > [ 117.534625] kmemleak: Kernel memory leak detector disabled
> > > [ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
> > > [ 117.535761] kmemleak: comm "cat", pid 177, jiffies
> > > 4294921177
> > > [ 117.536339] kmemleak: min_count = 1
> > > [ 117.536718] kmemleak: count = 0
> > > [ 117.537068] kmemleak: flags = 0x1
> > > [ 117.537429] kmemleak: checksum = 0
> > > [ 117.537806] kmemleak: backtrace:
> > > [ 117.538211] kmem_cache_alloc+0x23c/0x2f0
> > > [ 117.538924] test_version_show+0x1fc/0x3a0
> > > [ 117.539393] module_attr_show+0x28/0x40
> > > [ 117.539844] sysfs_kf_seq_show+0xb0/0x130
> > > [ 117.540304] kernfs_seq_show+0x30/0x40
> > > [ 117.540750] seq_read_iter+0x1bc/0x4b0
> > > [ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
> > > [ 117.541687] generic_file_splice_read+0xd0/0x184
> > > [ 117.542182] do_splice_to+0x90/0xe0
> > > [ 117.542611] splice_direct_to_actor+0xb8/0x250
> > > [ 117.543097] do_splice_direct+0x88/0xd4
> > > [ 117.543544] do_sendfile+0x2b0/0x344
> > > [ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
> > > [ 117.544471] invoke_syscall+0x48/0x114
> > > [ 117.544917] el0_svc_common.constprop.0+0x44/0xec
> > > [ 117.545416] do_el0_svc+0x74/0x90
> > > [ 117.554100] kmemleak: Automatic memory scanning thread ended
> > >
> > > Signed-off-by: Kuan-Ying Lee <[email protected]>
> > > ---
> > > mm/kmemleak.c | 17 ++++++++++++-----
> > > 1 file changed, 12 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> > > index b57383c17cf6..fa12e2e08cdc 100644
> > > --- a/mm/kmemleak.c
> > > +++ b/mm/kmemleak.c
> > > @@ -381,15 +381,20 @@ static void dump_object_info(struct
> > > kmemleak_object *object)
> > > static struct kmemleak_object *lookup_object(unsigned long ptr,
> > > int
> > > alias)
> > > {
> > > struct rb_node *rb = object_tree_root.rb_node;
> > > + unsigned long untagged_ptr = (unsigned
> > > long)kasan_reset_tag((void *)ptr);
> > >
> > > while (rb) {
> > > struct kmemleak_object *object =
> > > rb_entry(rb, struct kmemleak_object,
> > > rb_node);
> > > - if (ptr < object->pointer)
> > > + unsigned long untagged_objp;
> > > +
> > > + untagged_objp = (unsigned
> > > long)kasan_reset_tag((void
> > > *)object->pointer);
> > > +
> > > + if (untagged_ptr < untagged_objp)
> > > rb = object->rb_node.rb_left;
> > > - else if (object->pointer + object->size <= ptr)
> > > + else if (untagged_objp + object->size <=
> > > untagged_ptr)
> > > rb = object->rb_node.rb_right;
> > > - else if (object->pointer == ptr || alias)
> > > + else if (untagged_objp == untagged_ptr || alias)
> > > return object;
> > > else {
> > > kmemleak_warn("Found object by alias at
> > > 0x%08lx\n",
> > > @@ -576,6 +581,7 @@ static struct kmemleak_object
> > > *create_object(unsigned long ptr, size_t size,
> > > struct kmemleak_object *object, *parent;
> > > struct rb_node **link, *rb_parent;
> > > unsigned long untagged_ptr;
> > > + unsigned long untagged_objp;
> > >
> > > object = mem_pool_alloc(gfp);
> > > if (!object) {
> > > @@ -629,9 +635,10 @@ static struct kmemleak_object
> > > *create_object(unsigned long ptr, size_t size,
> > > while (*link) {
> > > rb_parent = *link;
> > > parent = rb_entry(rb_parent, struct
> > > kmemleak_object,
> > > rb_node);
> > > - if (ptr + size <= parent->pointer)
> > > + untagged_objp = (unsigned
> > > long)kasan_reset_tag((void
> > > *)parent->pointer);
> > > + if (untagged_ptr + size <= untagged_objp)
> > > link = &parent->rb_node.rb_left;
> > > - else if (parent->pointer + parent->size <= ptr)
> > > + else if (untagged_objp + parent->size <=
> > > untagged_ptr)
> > > link = &parent->rb_node.rb_right;
> > > else {
> > > kmemleak_stop("Cannot insert 0x%lx into the
> > > object search tree (overlaps existing)\n",
> > > --
> > > 2.18.0
> > >
> >
> > --
> > You received this message because you are subscribed to the Google
> > Groups "kasan-dev" group.
> > To unsubscribe from this group and stop receiving emails from it,
> > send an email to [email protected].
> > To view this discussion on the web visit
> > https://urldefense.com/v3/__https://groups.google.com/d/msgid/kasan-dev/754511d9a0368065768cc3ad8037184d62c3fbd1.camel*40mediatek.com__;JQ!!CTRNKA9wMg0ARbw!y7gGU0PsiMId4XiGTZzBUUL_WtWQ24nnTQtGbFrZ46wqfwk8ZeYCVP2pYmNFHrAUGOKr1g$
> > .
On Fri, 19 Nov 2021 23:12:55 +0800 Kuan-Ying Lee <[email protected]> wrote:
> > > > Call sequence:
> > > > ptr = kmalloc(size, GFP_KERNEL);
> > > > page = virt_to_page(ptr);
> > > > kfree(page_address(page));
> > > > ptr = kmalloc(size, GFP_KERNEL);
> >
> > How is this call sequence valid? page_address returns the address of
> > the start of the page, while kmalloced object could have been located
> > in the middle of it.
>
> Thanks for pointing out. I miss the offset.
>
> It should be listed as below.
>
> ptr = kmalloc(size, GFP_KERNEL);
> page = virt_to_page(ptr);
> offset = offset_in_page(ptr);
> kfree(page_address(page) + offset);
> ptr = kmalloc(size, GFP_KERNEL);
I updated the changelog to reflect this.
On Sat, 2021-11-20 at 06:43 +0800, Andrew Morton wrote:
> On Fri, 19 Nov 2021 23:12:55 +0800 Kuan-Ying Lee <
> [email protected]> wrote:
>
> > > > > Call sequence:
> > > > > ptr = kmalloc(size, GFP_KERNEL);
> > > > > page = virt_to_page(ptr);
> > > > > kfree(page_address(page));
> > > > > ptr = kmalloc(size, GFP_KERNEL);
> > >
> > > How is this call sequence valid? page_address returns the address
> > > of
> > > the start of the page, while kmalloced object could have been
> > > located
> > > in the middle of it.
> >
> > Thanks for pointing out. I miss the offset.
> >
> > It should be listed as below.
> >
> > ptr = kmalloc(size, GFP_KERNEL);
> > page = virt_to_page(ptr);
> > offset = offset_in_page(ptr);
> > kfree(page_address(page) + offset);
> > ptr = kmalloc(size, GFP_KERNEL);
>
> I updated the changelog to reflect this.
Thanks for updating changelog. :)
On Thu, Nov 18, 2021 at 10:20 AM Kuan-Ying Lee
<[email protected]> wrote:
>
> +Cc kasan group
>
> On Thu, 2021-11-18 at 13:44 +0800, Kuan-Ying Lee wrote:
> > With HW tag-based kasan enable, We will get the warning
> > when we free object whose address starts with 0xFF.
> >
> > It is because kmemleak rbtree stores tagged object and
> > this freeing object's tag does not match with rbtree object.
> >
> > In the example below, kmemleak rbtree stores the tagged object in
> > the kmalloc(), and kfree() gets the pointer with 0xFF tag.
> >
> > Call sequence:
> > ptr = kmalloc(size, GFP_KERNEL);
> > page = virt_to_page(ptr);
> > kfree(page_address(page));
> > ptr = kmalloc(size, GFP_KERNEL);
> >
> > Call sequence like that may cause the warning as following:
> > 1) Freeing unknown object:
> > In kfree(), we will get free unknown object warning in
> > kmemleak_free().
> > Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in kfree()
> > have
> > different tag.
> >
> > 2) Overlap existing:
> > When we allocate that object with the same hw-tag again, we will
> > find the overlap in the kmemleak rbtree and kmemleak thread will
> > be killed.
> >
> > [ 116.685312] kmemleak: Freeing unknown object at 0xffff000003f88000
> > [ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-dirty
> > #21
> > [ 116.687067] Hardware name: linux,dummy-virt (DT)
> > [ 116.687496] Call trace:
> > [ 116.687792] dump_backtrace+0x0/0x1ac
> > [ 116.688255] show_stack+0x1c/0x30
> > [ 116.688663] dump_stack_lvl+0x68/0x84
> > [ 116.689096] dump_stack+0x1c/0x38
> > [ 116.689499] kmemleak_free+0x6c/0x70
> > [ 116.689919] slab_free_freelist_hook+0x104/0x200
> > [ 116.690420] kmem_cache_free+0xa8/0x3d4
> > [ 116.690845] test_version_show+0x270/0x3a0
> > [ 116.691344] module_attr_show+0x28/0x40
> > [ 116.691789] sysfs_kf_seq_show+0xb0/0x130
> > [ 116.692245] kernfs_seq_show+0x30/0x40
> > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > [ 116.692678] seq_read_iter+0x1bc/0x4b0
> > [ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
> > [ 116.693586] generic_file_splice_read+0xd0/0x184
> > [ 116.694078] do_splice_to+0x90/0xe0
> > [ 116.694498] splice_direct_to_actor+0xb8/0x250
> > [ 116.694975] do_splice_direct+0x88/0xd4
> > [ 116.695409] do_sendfile+0x2b0/0x344
> > [ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
> > [ 116.696306] invoke_syscall+0x48/0x114
> > [ 116.696735] el0_svc_common.constprop.0+0x44/0xec
> > [ 116.697263] do_el0_svc+0x74/0x90
> > [ 116.697665] el0_svc+0x20/0x80
> > [ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
> > [ 116.698695] el0t_64_sync+0x1ac/0x1b0
> > ...
> > [ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into the
> > object search tree (overlaps existing)
> > [ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-dirty
> > #21
> > [ 117.521827] Hardware name: linux,dummy-virt (DT)
> > [ 117.522287] Call trace:
> > [ 117.522586] dump_backtrace+0x0/0x1ac
> > [ 117.523053] show_stack+0x1c/0x30
> > [ 117.523578] dump_stack_lvl+0x68/0x84
> > [ 117.524039] dump_stack+0x1c/0x38
> > [ 117.524472] create_object.isra.0+0x2d8/0x2fc
> > [ 117.524975] kmemleak_alloc+0x34/0x40
> > [ 117.525416] kmem_cache_alloc+0x23c/0x2f0
> > [ 117.525914] test_version_show+0x1fc/0x3a0
> > [ 117.526379] module_attr_show+0x28/0x40
> > [ 117.526827] sysfs_kf_seq_show+0xb0/0x130
> > [ 117.527363] kernfs_seq_show+0x30/0x40
> > [ 117.527848] seq_read_iter+0x1bc/0x4b0
> > [ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
> > [ 117.528809] generic_file_splice_read+0xd0/0x184
> > [ 117.529316] do_splice_to+0x90/0xe0
> > [ 117.529734] splice_direct_to_actor+0xb8/0x250
> > [ 117.530227] do_splice_direct+0x88/0xd4
> > [ 117.530686] do_sendfile+0x2b0/0x344
> > [ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
> > [ 117.531673] invoke_syscall+0x48/0x114
> > [ 117.532111] el0_svc_common.constprop.0+0x44/0xec
> > [ 117.532621] do_el0_svc+0x74/0x90
> > [ 117.533048] el0_svc+0x20/0x80
> > [ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
> > [ 117.533950] el0t_64_sync+0x1ac/0x1b0
> > [ 117.534625] kmemleak: Kernel memory leak detector disabled
> > [ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
> > [ 117.535761] kmemleak: comm "cat", pid 177, jiffies 4294921177
> > [ 117.536339] kmemleak: min_count = 1
> > [ 117.536718] kmemleak: count = 0
> > [ 117.537068] kmemleak: flags = 0x1
> > [ 117.537429] kmemleak: checksum = 0
> > [ 117.537806] kmemleak: backtrace:
> > [ 117.538211] kmem_cache_alloc+0x23c/0x2f0
> > [ 117.538924] test_version_show+0x1fc/0x3a0
> > [ 117.539393] module_attr_show+0x28/0x40
> > [ 117.539844] sysfs_kf_seq_show+0xb0/0x130
> > [ 117.540304] kernfs_seq_show+0x30/0x40
> > [ 117.540750] seq_read_iter+0x1bc/0x4b0
> > [ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
> > [ 117.541687] generic_file_splice_read+0xd0/0x184
> > [ 117.542182] do_splice_to+0x90/0xe0
> > [ 117.542611] splice_direct_to_actor+0xb8/0x250
> > [ 117.543097] do_splice_direct+0x88/0xd4
> > [ 117.543544] do_sendfile+0x2b0/0x344
> > [ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
> > [ 117.544471] invoke_syscall+0x48/0x114
> > [ 117.544917] el0_svc_common.constprop.0+0x44/0xec
> > [ 117.545416] do_el0_svc+0x74/0x90
> > [ 117.554100] kmemleak: Automatic memory scanning thread ended
> >
> > Signed-off-by: Kuan-Ying Lee <[email protected]>
> > ---
> > mm/kmemleak.c | 17 ++++++++++++-----
> > 1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> > index b57383c17cf6..fa12e2e08cdc 100644
> > --- a/mm/kmemleak.c
> > +++ b/mm/kmemleak.c
> > @@ -381,15 +381,20 @@ static void dump_object_info(struct
> > kmemleak_object *object)
> > static struct kmemleak_object *lookup_object(unsigned long ptr, int
> > alias)
> > {
> > struct rb_node *rb = object_tree_root.rb_node;
> > + unsigned long untagged_ptr = (unsigned
> > long)kasan_reset_tag((void *)ptr);
> >
> > while (rb) {
> > struct kmemleak_object *object =
> > rb_entry(rb, struct kmemleak_object, rb_node);
> > - if (ptr < object->pointer)
> > + unsigned long untagged_objp;
> > +
> > + untagged_objp = (unsigned long)kasan_reset_tag((void
> > *)object->pointer);
The two lines above can be squashed together.
> > +
> > + if (untagged_ptr < untagged_objp)
> > rb = object->rb_node.rb_left;
> > - else if (object->pointer + object->size <= ptr)
> > + else if (untagged_objp + object->size <= untagged_ptr)
> > rb = object->rb_node.rb_right;
> > - else if (object->pointer == ptr || alias)
> > + else if (untagged_objp == untagged_ptr || alias)
> > return object;
> > else {
> > kmemleak_warn("Found object by alias at
> > 0x%08lx\n",
> > @@ -576,6 +581,7 @@ static struct kmemleak_object
> > *create_object(unsigned long ptr, size_t size,
> > struct kmemleak_object *object, *parent;
> > struct rb_node **link, *rb_parent;
> > unsigned long untagged_ptr;
> > + unsigned long untagged_objp;
> >
> > object = mem_pool_alloc(gfp);
> > if (!object) {
> > @@ -629,9 +635,10 @@ static struct kmemleak_object
> > *create_object(unsigned long ptr, size_t size,
> > while (*link) {
> > rb_parent = *link;
> > parent = rb_entry(rb_parent, struct kmemleak_object,
> > rb_node);
> > - if (ptr + size <= parent->pointer)
> > + untagged_objp = (unsigned long)kasan_reset_tag((void
> > *)parent->pointer);
> > + if (untagged_ptr + size <= untagged_objp)
> > link = &parent->rb_node.rb_left;
> > - else if (parent->pointer + parent->size <= ptr)
> > + else if (untagged_objp + parent->size <= untagged_ptr)
> > link = &parent->rb_node.rb_right;
> > else {
> > kmemleak_stop("Cannot insert 0x%lx into the
> > object search tree (overlaps existing)\n",
> > --
> > 2.18.0
> >
>
> --
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On Thu, 25 Nov 2021 17:13:36 +0100 Andrey Konovalov <[email protected]> wrote:
> > > kmemleak_object *object)
> > > static struct kmemleak_object *lookup_object(unsigned long ptr, int
> > > alias)
> > > {
> > > struct rb_node *rb = object_tree_root.rb_node;
> > > + unsigned long untagged_ptr = (unsigned
> > > long)kasan_reset_tag((void *)ptr);
> > >
> > > while (rb) {
> > > struct kmemleak_object *object =
> > > rb_entry(rb, struct kmemleak_object, rb_node);
> > > - if (ptr < object->pointer)
> > > + unsigned long untagged_objp;
> > > +
> > > + untagged_objp = (unsigned long)kasan_reset_tag((void
> > > *)object->pointer);
>
> The two lines above can be squashed together.
That would make a too-long line even longer. In fact I think it's
better to go the other way:
--- a/mm/kmemleak.c~kmemleak-fix-kmemleak-false-positive-report-with-hw-tag-based-kasan-enable-fix
+++ a/mm/kmemleak.c
@@ -384,10 +384,10 @@ static struct kmemleak_object *lookup_ob
unsigned long untagged_ptr = (unsigned long)kasan_reset_tag((void *)ptr);
while (rb) {
- struct kmemleak_object *object =
- rb_entry(rb, struct kmemleak_object, rb_node);
+ 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);
if (untagged_ptr < untagged_objp)
_
On Thu, Nov 18, 2021 at 01:44:19PM +0800, Kuan-Ying Lee wrote:
> With HW tag-based kasan enable, We will get the warning
> when we free object whose address starts with 0xFF.
>
> It is because kmemleak rbtree stores tagged object and
> this freeing object's tag does not match with rbtree object.
>
> In the example below, kmemleak rbtree stores the tagged object in
> the kmalloc(), and kfree() gets the pointer with 0xFF tag.
>
> Call sequence:
> ptr = kmalloc(size, GFP_KERNEL);
> page = virt_to_page(ptr);
> kfree(page_address(page));
> ptr = kmalloc(size, GFP_KERNEL);
>
> Call sequence like that may cause the warning as following:
> 1) Freeing unknown object:
> In kfree(), we will get free unknown object warning in kmemleak_free().
> Because object(0xFx) in kmemleak rbtree and pointer(0xFF) in kfree() have
> different tag.
>
> 2) Overlap existing:
> When we allocate that object with the same hw-tag again, we will
> find the overlap in the kmemleak rbtree and kmemleak thread will
> be killed.
>
> [ 116.685312] kmemleak: Freeing unknown object at 0xffff000003f88000
> [ 116.686422] CPU: 5 PID: 177 Comm: cat Not tainted 5.16.0-rc1-dirty #21
> [ 116.687067] Hardware name: linux,dummy-virt (DT)
> [ 116.687496] Call trace:
> [ 116.687792] dump_backtrace+0x0/0x1ac
> [ 116.688255] show_stack+0x1c/0x30
> [ 116.688663] dump_stack_lvl+0x68/0x84
> [ 116.689096] dump_stack+0x1c/0x38
> [ 116.689499] kmemleak_free+0x6c/0x70
> [ 116.689919] slab_free_freelist_hook+0x104/0x200
> [ 116.690420] kmem_cache_free+0xa8/0x3d4
> [ 116.690845] test_version_show+0x270/0x3a0
> [ 116.691344] module_attr_show+0x28/0x40
> [ 116.691789] sysfs_kf_seq_show+0xb0/0x130
> [ 116.692245] kernfs_seq_show+0x30/0x40
> [ 116.692678] seq_read_iter+0x1bc/0x4b0
> [ 116.692678] seq_read_iter+0x1bc/0x4b0
> [ 116.693114] kernfs_fop_read_iter+0x144/0x1c0
> [ 116.693586] generic_file_splice_read+0xd0/0x184
> [ 116.694078] do_splice_to+0x90/0xe0
> [ 116.694498] splice_direct_to_actor+0xb8/0x250
> [ 116.694975] do_splice_direct+0x88/0xd4
> [ 116.695409] do_sendfile+0x2b0/0x344
> [ 116.695829] __arm64_sys_sendfile64+0x164/0x16c
> [ 116.696306] invoke_syscall+0x48/0x114
> [ 116.696735] el0_svc_common.constprop.0+0x44/0xec
> [ 116.697263] do_el0_svc+0x74/0x90
> [ 116.697665] el0_svc+0x20/0x80
> [ 116.698261] el0t_64_sync_handler+0x1a8/0x1b0
> [ 116.698695] el0t_64_sync+0x1ac/0x1b0
> ...
> [ 117.520301] kmemleak: Cannot insert 0xf2ff000003f88000 into the object search tree (overlaps existing)
> [ 117.521118] CPU: 5 PID: 178 Comm: cat Not tainted 5.16.0-rc1-dirty #21
> [ 117.521827] Hardware name: linux,dummy-virt (DT)
> [ 117.522287] Call trace:
> [ 117.522586] dump_backtrace+0x0/0x1ac
> [ 117.523053] show_stack+0x1c/0x30
> [ 117.523578] dump_stack_lvl+0x68/0x84
> [ 117.524039] dump_stack+0x1c/0x38
> [ 117.524472] create_object.isra.0+0x2d8/0x2fc
> [ 117.524975] kmemleak_alloc+0x34/0x40
> [ 117.525416] kmem_cache_alloc+0x23c/0x2f0
> [ 117.525914] test_version_show+0x1fc/0x3a0
> [ 117.526379] module_attr_show+0x28/0x40
> [ 117.526827] sysfs_kf_seq_show+0xb0/0x130
> [ 117.527363] kernfs_seq_show+0x30/0x40
> [ 117.527848] seq_read_iter+0x1bc/0x4b0
> [ 117.528320] kernfs_fop_read_iter+0x144/0x1c0
> [ 117.528809] generic_file_splice_read+0xd0/0x184
> [ 117.529316] do_splice_to+0x90/0xe0
> [ 117.529734] splice_direct_to_actor+0xb8/0x250
> [ 117.530227] do_splice_direct+0x88/0xd4
> [ 117.530686] do_sendfile+0x2b0/0x344
> [ 117.531154] __arm64_sys_sendfile64+0x164/0x16c
> [ 117.531673] invoke_syscall+0x48/0x114
> [ 117.532111] el0_svc_common.constprop.0+0x44/0xec
> [ 117.532621] do_el0_svc+0x74/0x90
> [ 117.533048] el0_svc+0x20/0x80
> [ 117.533461] el0t_64_sync_handler+0x1a8/0x1b0
> [ 117.533950] el0t_64_sync+0x1ac/0x1b0
> [ 117.534625] kmemleak: Kernel memory leak detector disabled
> [ 117.535201] kmemleak: Object 0xf2ff000003f88000 (size 128):
> [ 117.535761] kmemleak: comm "cat", pid 177, jiffies 4294921177
> [ 117.536339] kmemleak: min_count = 1
> [ 117.536718] kmemleak: count = 0
> [ 117.537068] kmemleak: flags = 0x1
> [ 117.537429] kmemleak: checksum = 0
> [ 117.537806] kmemleak: backtrace:
> [ 117.538211] kmem_cache_alloc+0x23c/0x2f0
> [ 117.538924] test_version_show+0x1fc/0x3a0
> [ 117.539393] module_attr_show+0x28/0x40
> [ 117.539844] sysfs_kf_seq_show+0xb0/0x130
> [ 117.540304] kernfs_seq_show+0x30/0x40
> [ 117.540750] seq_read_iter+0x1bc/0x4b0
> [ 117.541206] kernfs_fop_read_iter+0x144/0x1c0
> [ 117.541687] generic_file_splice_read+0xd0/0x184
> [ 117.542182] do_splice_to+0x90/0xe0
> [ 117.542611] splice_direct_to_actor+0xb8/0x250
> [ 117.543097] do_splice_direct+0x88/0xd4
> [ 117.543544] do_sendfile+0x2b0/0x344
> [ 117.543983] __arm64_sys_sendfile64+0x164/0x16c
> [ 117.544471] invoke_syscall+0x48/0x114
> [ 117.544917] el0_svc_common.constprop.0+0x44/0xec
> [ 117.545416] do_el0_svc+0x74/0x90
> [ 117.554100] kmemleak: Automatic memory scanning thread ended
>
> Signed-off-by: Kuan-Ying Lee <[email protected]>
I was wondering whether we should just give up the tag when storing the
object->pointer and avoid any later untagging when searching the rb
tree. But, if we want to keep that for debugging, fine by me as well.
Reviewed-by: Catalin Marinas <[email protected]>
--
Catalin