linux-kernel - [PATCH bpf-next v3 2/2] bpf: Expose bpf_d

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Message-Id: <20201113005930.541956-3-kpsingh@chromium.org>
Date:   Fri, 13 Nov 2020 00:59:30 +0000
From:   KP Singh <kpsingh@...omium.org>
To:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Cc:     Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Jann Horn <jannh@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>
Subject: [PATCH bpf-next v3 2/2] bpf: Expose bpf_d_path helper to sleepable LSM hooks

From: KP Singh <kpsingh@...gle.com>

Sleepable hooks are never called from an NMI/interrupt context, so it is
safe to use the bpf_d_path helper in LSM programs attaching to these
hooks.

The helper is not restricted to sleepable programs and merely uses the
list of sleeable hooks as the initial subset of LSM hooks where it can
be used.

Acked-by: Andrii Nakryiko <andrii@...nel.org>

Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 kernel/trace/bpf_trace.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index e4515b0f62a8..eab1af02c90d 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -16,6 +16,7 @@
 #include <linux/syscalls.h>
 #include <linux/error-injection.h>
 #include <linux/btf_ids.h>
+#include <linux/bpf_lsm.h>
 
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/btf.h>
@@ -1178,7 +1179,11 @@ BTF_SET_END(btf_allowlist_d_path)
 
 static bool bpf_d_path_allowed(const struct bpf_prog *prog)
 {
-	return btf_id_set_contains(&btf_allowlist_d_path, prog->aux->attach_btf_id);
+	if (prog->type == BPF_PROG_TYPE_LSM)
+		return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
+
+	return btf_id_set_contains(&btf_allowlist_d_path,
+				   prog->aux->attach_btf_id);
 }
 
 BTF_ID_LIST_SINGLE(bpf_d_path_btf_ids, struct, path)
-- 
2.29.2.299.gdc1121823c-goog