On 7/18/22 7:36 AM, Benjamin Tissoires wrote:
On Sat, Jul 16, 2022 at 6:29 AM Yonghong Song <yhs@xxxxxx> wrote:
On 7/12/22 7:58 AM, Benjamin Tissoires wrote:
When a kfunc is not returning a pointer to a struct but to a plain type,
we can consider it is a valid allocated memory assuming that:
- one of the arguments is either called rdonly_buf_size or
rdwr_buf_size
- and this argument is a const from the caller point of view
We can then use this parameter as the size of the allocated memory.
The memory is either read-only or read-write based on the name
of the size parameter.
If I understand correctly, this permits a kfunc like
int *kfunc(..., int rdonly_buf_size);
...
int *p = kfunc(..., 20);
so the 'p' points to a memory buffer with size 20.
Yes, exactly.
This looks like a strange interface although probably there
is a valid reason for this as I didn't participated in
earlier discussions.
Well, the point is I need to be able to access a memory region that
was allocated dynamically. For drivers, the incoming data can not
usually be bound to a static value, and so we can not have the data
statically defined in the matching struct.
So this allows defining a kfunc to return any memory properly
allocated and owned by the device.
Okay, thanks for explanation.
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
---
changes in v6:
- code review from Kartikeya:
- remove comment change that had no reasons to be
- remove handling of PTR_TO_MEM with kfunc releases
- introduce struct bpf_kfunc_arg_meta
- do rdonly/rdwr_buf_size check in btf_check_kfunc_arg_match
- reverted most of the changes in verifier.c
- make sure kfunc acquire is using a struct pointer, not just a plain
pointer
- also forward ref_obj_id to PTR_TO_MEM in kfunc to not use after free
the allocated memory
changes in v5:
- updated PTR_TO_MEM comment in btf.c to match upstream
- make it read-only or read-write based on the name of size
new in v4
---
include/linux/bpf.h | 10 ++++++-
include/linux/btf.h | 12 ++++++++
kernel/bpf/btf.c | 67 ++++++++++++++++++++++++++++++++++++++++---
kernel/bpf/verifier.c | 49 +++++++++++++++++++++++--------
4 files changed, 121 insertions(+), 17 deletions(-)
[...]
