bpf: Add support for bpf_get_func_ip helper for uprobe program

Adding support for bpf_get_func_ip helper for uprobe program to return
probed address for both uprobe and return uprobe.

We discussed this in [1] and agreed that uprobe can have special use
of bpf_get_func_ip helper that differs from kprobe.

The kprobe bpf_get_func_ip returns:
  - address of the function if probe is attach on function entry
    for both kprobe and return kprobe
  - 0 if the probe is not attach on function entry

The uprobe bpf_get_func_ip returns:
  - address of the probe for both uprobe and return uprobe

The reason for this semantic change is that kernel can't really tell
if the probe user space address is function entry.

The uprobe program is actually kprobe type program attached as uprobe.
One of the consequences of this design is that uprobes do not have its
own set of helpers, but share them with kprobes.

As we need different functionality for bpf_get_func_ip helper for uprobe,
I'm adding the bool value to the bpf_trace_run_ctx, so the helper can
detect that it's executed in uprobe context and call specific code.

The is_uprobe bool is set as true in bpf_prog_run_array_sleepable, which
is currently used only for executing bpf programs in uprobe.

Renaming bpf_prog_run_array_sleepable to bpf_prog_run_array_uprobe
to address that it's only used for uprobes and that it sets the
run_ctx.is_uprobe as suggested by Yafang Shao.

Suggested-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
[1] https://lore.kernel.org/bpf/CAEf4BzZ=xLVkG5eurEuvLU79wAMtwho7ReR+XJAgwhFF4M-7Cg@mail.gmail.com/
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Viktor Malik <vmalik@redhat.com>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230807085956.2344866-2-jolsa@kernel.org
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 70da852..d21deb4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5086,9 +5086,14 @@ union bpf_attr {
  * u64 bpf_get_func_ip(void *ctx)
  * 	Description
  * 		Get address of the traced function (for tracing and kprobe programs).
+ *
+ * 		When called for kprobe program attached as uprobe it returns
+ * 		probe address for both entry and return uprobe.
+ *
  * 	Return
- * 		Address of the traced function.
+ * 		Address of the traced function for kprobe.
  * 		0 for kprobes placed within the function (not at the entry).
+ * 		Address of the probe for uprobe and return uprobe.
  *
  * u64 bpf_get_attach_cookie(void *ctx)
  * 	Description