netdev - [PATCH v1 bpf 2/4] bpf: Fix data-races around bpf_jit

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Message-ID: <20220818042339.82992-3-kuniyu@amazon.com>
Date:   Wed, 17 Aug 2022 21:23:37 -0700
From:   Kuniyuki Iwashima <kuniyu@...zon.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
CC:     Kuniyuki Iwashima <kuniyu@...zon.com>,
        Kuniyuki Iwashima <kuni1840@...il.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH v1 bpf 2/4] bpf: Fix data-races around bpf_jit_harden.

While reading bpf_jit_harden, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its readers.

Fixes: 4f3446bb809f ("bpf: add generic constant blinding for use in jits")
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
 include/linux/filter.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/include/linux/filter.h b/include/linux/filter.h
index ce8072626ccf..09566ad211bd 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -1090,6 +1090,8 @@ static inline bool bpf_prog_ebpf_jited(const struct bpf_prog *fp)
 
 static inline bool bpf_jit_blinding_enabled(struct bpf_prog *prog)
 {
+	int jit_harden = READ_ONCE(bpf_jit_harden);
+
 	/* These are the prerequisites, should someone ever have the
 	 * idea to call blinding outside of them, we make sure to
 	 * bail out.
@@ -1098,9 +1100,9 @@ static inline bool bpf_jit_blinding_enabled(struct bpf_prog *prog)
 		return false;
 	if (!prog->jit_requested)
 		return false;
-	if (!bpf_jit_harden)
+	if (!jit_harden)
 		return false;
-	if (bpf_jit_harden == 1 && capable(CAP_SYS_ADMIN))
+	if (jit_harden == 1 && capable(CAP_SYS_ADMIN))
 		return false;
 
 	return true;
@@ -1111,7 +1113,7 @@ static inline bool bpf_jit_kallsyms_enabled(void)
 	/* There are a couple of corner cases where kallsyms should
 	 * not be enabled f.e. on hardening.
 	 */
-	if (bpf_jit_harden)
+	if (READ_ONCE(bpf_jit_harden))
 		return false;
 	if (!bpf_jit_kallsyms)
 		return false;
-- 
2.30.2