[PATCH AUTOSEL 6.0 69/77] bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT

Sasha Levin
2022-10-09T22:20:36Z

From: Jiri Olsa <jolsa@kernel.org>

[ Upstream commit c09eb2e578eb1668bbc84dc07e8d8bd6f04b9a02 ]

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 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.

Also renaming kprobe_multi_link_handler entry_ip argument to fentry_ip
so it's clearer this is an ftrace __fentry__ ip.

[1] commit 7f0059b58f02 ("selftests/bpf: Fix kprobe_multi test.")

Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Martynas Pumputis <m@lambda.lt>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-5-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/trace/bpf_trace.c | 20 +++++++++++++++++--
.../selftests/bpf/progs/kprobe_multi.c | 4 +---
2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 68e5cdd24cef..b1daf7c9b895 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1026,6 +1026,22 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = {
.arg1_type = ARG_PTR_TO_CTX,
};

+#ifdef CONFIG_X86_KERNEL_IBT
+static unsigned long get_entry_ip(unsigned long fentry_ip)
+{
+ u32 instr;
+
+ /* Being extra safe in here in case entry ip is on the page-edge. */
+ if (get_kernel_nofault(instr, (u32 *) fentry_ip - 1))
+ return fentry_ip;
+ if (is_endbr(instr))
+ fentry_ip -= ENDBR_INSN_SIZE;
+ return fentry_ip;
+}
+#else
+#define get_entry_ip(fentry_ip) fentry_ip
+#endif
+
BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
{
struct kprobe *kp = kprobe_running();
@@ -2414,13 +2430,13 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link,
}

static void
-kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,
+kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,
struct pt_regs *regs)
{
struct bpf_kprobe_multi_link *link;

link = container_of(fp, struct bpf_kprobe_multi_link, fp);
- kprobe_multi_link_prog_run(link, entry_ip, regs);
+ kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);
}

static int symbols_cmp_r(const void *a, const void *b, const void *priv)
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi.c b/tools/testing/selftests/bpf/progs/kprobe_multi.c
index 08f95a8155d1..98c3399e15c0 100644
--- a/tools/testing/selftests/bpf/progs/kprobe_multi.c
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi.c
@@ -36,15 +36,13 @@ __u64 kretprobe_test6_result = 0;
__u64 kretprobe_test7_result = 0;
__u64 kretprobe_test8_result = 0;

-extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak;
-
static void kprobe_multi_check(void *ctx, bool is_return)
{
if (bpf_get_current_pid_tgid() >> 32 != pid)
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) && \
--
2.35.1