On Mon, Jan 27, 2025 at 2:54 PM Andrei Matei <andreimatei1@xxxxxxxxx> wrote: > > On Mon, Jan 27, 2025 at 5:04 PM Alexei Starovoitov > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > On Sat, Jan 25, 2025 at 5:05 PM Levi Zim <rsworktech@xxxxxxxxxxx> wrote: > > > > > > On 2025/1/26 00:58, Alexei Starovoitov wrote: > > > > On Sat, Jan 25, 2025 at 12:30 AM Levi Zim via B4 Relay > > > > <devnull+rsworktech.outlook.com@xxxxxxxxxx> wrote: > > > >> From: Levi Zim <rsworktech@xxxxxxxxxxx> > > > >> > > > >> This patch add a helper function bpf_probe_read_kernel_dynptr: > > > >> > > > >> long bpf_probe_read_kernel_dynptr(const struct bpf_dynptr *dst, > > > >> u32 offset, u32 size, const void *unsafe_ptr, u64 flags); > > > > We stopped adding helpers years ago. > > > > Only new kfuncs are allowed. > > > > > > Sorry, I didn't know that. Just asking, is there any > > > documentation/discussion > > > about stopping adding helpers? > > > > > > I will switch the implementation to kfuncs in v3. > > > > > > > This particular one doesn't look useful as-is. > > > > The same logic can be expressed with > > > > - create dynptr > > > > - dynptr_slice > > > > - copy_from_kernel > > > > > > By copy_from_kernel I assume you mean bpf_probe_read_kernel. The problem > > > with dynptr_slice_rdwr and probe_read_kernel is that they only support a > > > compile-time constant size [1]. > > > > > > But in order to best utilize the space on a BPF ringbuf, it is possible > > > to reserve a > > > variable length of space as dynptr on a ringbuf with > > > bpf_ringbuf_reserve_dynptr. > > For our uprobes, we've run into similar issues around doing variable-sized > bpf_probe_read_user() into ring buffers for our debugger [1]. Our use case > is that we generate uprobes that recursively read data structures until we > fill up a buffer. The verifier's insistence on knowing statically that a read > fits into the buffer makes for awkward code, and makes it hard to pack the > buffer fully; we have to split our reads into a couple of static size classes. > > Any chance there'd be interest in taking the opportunity to support > dynamically-sized reads from userspace too? :) That's bpf_probe_read_user_dynptr() from patch #2, no? But generally speaking, here's a list of new APIs that we'd need to cover all existing fixed buffer versions: - non-sleepable probe reads: bpf_probe_read_kernel_dynptr() bpf_probe_read_user_dynptr() bpf_probe_read_kernel_str_dynptr() bpf_probe_read_user_str_dynptr() - sleepable probe reads (copy_from_user): bpf_copy_from_user_dynptr() bpf_copy_from_user_str_dynptr() - and then we have complementary task-based APIs for non-current process: bpf_probe_read_user_task_dynptr() bpf_probe_read_user_str_task_dynptr() bpf_copy_from_user_task_dynptr() bpf_copy_from_user_str_task_dynptr() Jordan is working on non-dynptr version of bpf_copy_from_user_str_task(), once he's done with that, we'll add dynptr version, probably. > > [1] https://side-eye.io > > > > > That makes sense. The commit log didn't call it out. > > Please spell out the motivation clearly. > > Also why bpf_probe_read_kernel_common ? > > Do we need to memset() it on failure? > >
