On 8/22/23 12:19 PM, David Marchevsky wrote:
On 8/22/23 1:42 PM, Yonghong Song wrote:
On 8/21/23 10:05 PM, Dave Marchevsky wrote:
This patch adds kfuncs bpf_iter_task_vma_{new,next,destroy} which allow
creation and manipulation of struct bpf_iter_task_vma in open-coded
iterator style. BPF programs can use these kfuncs directly or through
bpf_for_each macro for natural-looking iteration of all task vmas.
The implementation borrows heavily from bpf_find_vma helper's locking -
differing only in that it holds the mmap_read lock for all iterations
while the helper only executes its provided callback on a maximum of 1
vma. Aside from locking, struct vma_iterator and vma_next do all the
heavy lifting.
The newly-added struct bpf_iter_task_vma has a name collision with a
selftest for the seq_file task_vma iter's bpf skel, so the selftests/bpf/progs
file is renamed in order to avoid the collision.
A pointer to an inner data struct, struct bpf_iter_task_vma_kern_data, is the
only field in struct bpf_iter_task_vma. This is because the inner data
struct contains a struct vma_iterator (not ptr), whose size is likely to
change under us. If bpf_iter_task_vma_kern contained vma_iterator directly
such a change would require change in opaque bpf_iter_task_vma struct's
size. So better to allocate vma_iterator using BPF allocator, and since
that alloc must already succeed, might as well allocate all iter fields,
thereby freezing struct bpf_iter_task_vma size.
Signed-off-by: Dave Marchevsky <davemarchevsky@xxxxxx>
Cc: Nathan Slingerland <slinger@xxxxxxxx>
---
include/uapi/linux/bpf.h | 4 +
kernel/bpf/helpers.c | 3 +
kernel/bpf/task_iter.c | 84 +++++++++++++++++++
tools/include/uapi/linux/bpf.h | 4 +
tools/lib/bpf/bpf_helpers.h | 8 ++
.../selftests/bpf/prog_tests/bpf_iter.c | 26 +++---
...f_iter_task_vma.c => bpf_iter_task_vmas.c} | 0
7 files changed, 116 insertions(+), 13 deletions(-)
rename tools/testing/selftests/bpf/progs/{bpf_iter_task_vma.c => bpf_iter_task_vmas.c} (100%)
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 8790b3962e4b..49fc1989a548 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -7311,4 +7311,8 @@ struct bpf_iter_num {
__u64 __opaque[1];
} __attribute__((aligned(8)));
+struct bpf_iter_task_vma {
+ __u64 __opaque[1]; /* See bpf_iter_num comment above */
+} __attribute__((aligned(8)));
In the future, we might have bpf_iter_cgroup, bpf_iter_task, bpf_iter_cgroup_task, etc. They may all use the same struct
like
struct bpf_iter_<...> {
__u64 __opaque[1];
} __attribute__((aligned(8)));
Maybe we want a generic one instead of having lots of
structs with the same underline definition? For example,
struct bpf_iter_generic
?
The bpf_for_each macro assumes a consistent naming scheme for opaque iter struct
and associated kfuncs. Having a 'bpf_iter_generic' shared amongst multiple types
of iters would break the scheme. We could:
* Add bpf_for_each_generic that only uses bpf_iter_generic
* This exposes implementation details in an ugly way, though.
* Do some macro magic to pick bpf_iter_generic for some types of iters, and
use consistent naming pattern for others.
* I'm not sure how to do this with preprocessor
* Migrate all opaque iter structs to only contain pointer to bpf_mem_alloc'd
data struct, and use bpf_iter_generic for all of them
* Probably need to see more iter implementation / usage before making such
a change
* Do 'typedef __u64 __aligned(8) bpf_iter_<...>
* BTF_KIND_TYPEDEF intead of BTF_KIND_STRUCT might throw off some verifier
logic. Could do similar typedef w/ struct to try to work around
it.
Let me know what you think. Personally I considered doing typedef while
implementing this, so that's the alternative I'd choose.
Okay, since we have naming convention restriction, typedef probably the
best option, something like
typedef struct bpf_iter_num bpf_iter_task_vma
?
Verifier might need to be changed if verifier strips all modifiers
(including tyypedef) to find the struct name.
+
#endif /* _UAPI__LINUX_BPF_H__ */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index eb91cae0612a..7a06dea749f1 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2482,6 +2482,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_slice_rdwr, KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_num_new, KF_ITER_NEW)
BTF_ID_FLAGS(func, bpf_iter_num_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_num_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_new, KF_ITER_NEW)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_next, KF_ITER_NEXT | KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_iter_task_vma_destroy, KF_ITER_DESTROY)
BTF_ID_FLAGS(func, bpf_dynptr_adjust)
BTF_ID_FLAGS(func, bpf_dynptr_is_null)
BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index c4ab9d6cdbe9..51c2dce435c1 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -7,7 +7,9 @@
#include <linux/fs.h>
#include <linux/fdtable.h>
#include <linux/filter.h>
+#include <linux/bpf_mem_alloc.h>
#include <linux/btf_ids.h>
+#include <linux/mm_types.h>
#include "mmap_unlock_work.h"
static const char * const iter_task_type_names[] = {
@@ -823,6 +825,88 @@ const struct bpf_func_proto bpf_find_vma_proto = {
.arg5_type = ARG_ANYTHING,
};
+struct bpf_iter_task_vma_kern_data {
+ struct task_struct *task;
+ struct mm_struct *mm;
+ struct mmap_unlock_irq_work *work;
+ struct vma_iterator vmi;
+};
+
+/* Non-opaque version of uapi bpf_iter_task_vma */
+struct bpf_iter_task_vma_kern {
+ struct bpf_iter_task_vma_kern_data *data;
+} __attribute__((aligned(8)));
+
+__bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it,
+ struct task_struct *task, u64 addr)
+{
+ struct bpf_iter_task_vma_kern *kit = (void *)it;
+ bool irq_work_busy = false;
+ int err;
+
+ BUILD_BUG_ON(sizeof(struct bpf_iter_task_vma_kern) != sizeof(struct bpf_iter_task_vma));
+ BUILD_BUG_ON(__alignof__(struct bpf_iter_task_vma_kern) != __alignof__(struct bpf_iter_task_vma));
+
+ /* is_iter_reg_valid_uninit guarantees that kit hasn't been initialized
+ * before, so non-NULL kit->data doesn't point to previously
+ * bpf_mem_alloc'd bpf_iter_task_vma_kern_data
+ */
+ kit->data = bpf_mem_alloc(&bpf_global_ma, sizeof(struct bpf_iter_task_vma_kern_data));
+ if (!kit->data)
+ return -ENOMEM;
+ kit->data->task = NULL;
+
+ if (!task) {
+ err = -ENOENT;
+ goto err_cleanup_iter;
+ }
+
+ kit->data->task = get_task_struct(task);
The above is not safe. Since there is no restriction on 'task',
the 'task' could be in a state for destruction with 'usage' count 0
and then get_task_struct(task) won't work since it unconditionally
tries to increase 'usage' count from 0 to 1.
Or, 'task' may be valid at the entry of the funciton, but when
'task' is in get_task_struct(), 'task' may have been destroyed
and 'task' memory is reused by somebody else.
I suggest that we check input parameter 'task' must be
PTR_TRUSTED or MEM_RCU. This way, the above !task checking
is not necessary and get_task_struct() can correctly
hold a reference to 'task'.
Adding a PTR_TRUSTED or MEM_RCU check seems reasonable. I'm curious
whether there's any way to feed a 'plain' struct task_struct PTR_TO_BTF_ID
to this kfunc currently.
* bpf_get_current_task_btf helper returns PTR_TRUSTED | PTR_TO_BTF_ID
* ptr hop from trusted task_struct to 'real_parent' or similar should
yield MEM_RCU (due to BTF_TYPE_SAFE_RCU(struct task_struct) def
This is true.
* if task kptr is in map_val, direct reference to it should result
in PTR_UNTRUSTED PTR_TO_BTF_ID, must kptr_xchg it or acquire again
using bpf_task_from_pid (?)
If in the rcu region, direct access of the task kptr can be marked
with MEM_RCU | PTR_MAYBE_NULL. After a null ptr check, you will
get a rcu protected task ptr.
But regardless, better to be explicit. Will change.
+ kit->data->mm = task->mm;
+ if (!kit->data->mm) {
+ err = -ENOENT;
+ goto err_cleanup_iter;
+ }
+
+ /* kit->data->work == NULL is valid after bpf_mmap_unlock_get_irq_work */
+ irq_work_busy = bpf_mmap_unlock_get_irq_work(&kit->data->work);
+ if (irq_work_busy || !mmap_read_trylock(kit->data->mm)) {
+ err = -EBUSY;
+ goto err_cleanup_iter;
+ }
+
+ vma_iter_init(&kit->data->vmi, kit->data->mm, addr);
+ return 0;
+
+err_cleanup_iter:
+ if (kit->data->task)
+ put_task_struct(kit->data->task);
+ bpf_mem_free(&bpf_global_ma, kit->data);
+ /* NULL kit->data signals failed bpf_iter_task_vma initialization */
+ kit->data = NULL;
+ return err;
+}
+
[...]
