bpf: Add bpf_has_frame_pointer()

Introduce a bpf_has_frame_pointer() helper that unwinders can call to
determine whether a given instruction pointer is within the valid frame
pointer region of a BPF JIT program or trampoline (i.e., after the
prologue, before the epilogue).

This will enable livepatch (with the ORC unwinder) to reliably unwind
through BPF JIT frames.

Acked-by: Song Liu <song@kernel.org>
Acked-and-tested-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/fd2bc5b4e261a680774b28f6100509fd5ebad2f0.1764818927.git.jpoimboe@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>

1 files changed, 16 insertions, 0 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c8ae6ab31651..1b9b18e5b03c 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -760,6 +760,22 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
 	       NULL;
 }
 
+bool bpf_has_frame_pointer(unsigned long ip)
+{
+	struct bpf_ksym *ksym;
+	unsigned long offset;
+
+	guard(rcu)();
+
+	ksym = bpf_ksym_find(ip);
+	if (!ksym || !ksym->fp_start || !ksym->fp_end)
+		return false;
+
+	offset = ip - ksym->start;
+
+	return offset >= ksym->fp_start && offset < ksym->fp_end;
+}
+
 const struct exception_table_entry *search_bpf_extables(unsigned long addr)
 {
 	const struct exception_table_entry *e = NULL;