Martynas reported bpf_get_func_ip returning +4 address when
CONFIG_X86_KERNEL_IBT option is enabled.
When CONFIG_X86_KERNEL_IBT is enabled we'll have endbr instruction
at the function entry, which screws return value of bpf_get_func_ip()
helper that should return the function address.
There's short term workaround [1] for kprobe_multi bpf program made
by Alexei [1], but we need this fixup also for bpf_get_attach_cookie,
that returns cookie based on the entry_ip value.
Moving the fixup in the fprobe handler, so both bpf_get_func_ip
and bpf_get_attach_cookie get expected function address when
CONFIG_X86_KERNEL_IBT option is enabled.
Keeping the resolved 'addr' in kallsyms_callback, instead of taking
ftrace_location value, because we depend on symbol address in the
cookie related code. With CONFIG_X86_KERNEL_IBT option the
ftrace_location value differs from symbol address.
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Reported-by: Martynas Pumputis <m@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
kernel/trace/bpf_trace.c | 4 ++++
tools/testing/selftests/bpf/progs/kprobe_multi.c | 2 +-
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 68e5cdd24cef..bcada91b0b3b 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2419,6 +2419,10 @@ kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
{
struct bpf_kprobe_multi_link *link;
+#ifdef CONFIG_X86_KERNEL_IBT
+ if (is_endbr(*((u32 *) entry_ip - 1)))
+ entry_ip -= ENDBR_INSN_SIZE;
+#endif
link = container_of(fp, struct bpf_kprobe_multi_link, fp);
kprobe_multi_link_prog_run(link, entry_ip, regs);
}
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi.c b/tools/testing/selftests/bpf/progs/kprobe_multi.c
index 08f95a8155d1..f165615d0b78 100644
--- a/tools/testing/selftests/bpf/progs/kprobe_multi.c
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi.c
@@ -44,7 +44,7 @@ static void kprobe_multi_check(void *ctx, bool is_return)
return;
__u64 cookie = test_cookie ? bpf_get_attach_cookie(ctx) : 0;
- __u64 addr = bpf_get_func_ip(ctx) - (CONFIG_X86_KERNEL_IBT ? 4 : 0);
+ __u64 addr = bpf_get_func_ip(ctx);
#define SET(__var, __addr, __cookie) ({ \
if (((const void *) addr == __addr) && \
--
2.35.3
