linux-kernel - [PATCH bpf-next 1/1] bpf: fix WARNING in __bpf_prog_ret0

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Message-ID: <20250526133358.2594176-1-mannkafai@gmail.com>
Date: Mon, 26 May 2025 21:33:58 +0800
From: KaFai Wan <mannkafai@...il.com>
To: ast@...nel.org,
	daniel@...earbox.net,
	john.fastabend@...il.com,
	andrii@...nel.org,
	martin.lau@...ux.dev,
	eddyz87@...il.com,
	song@...nel.org,
	yonghong.song@...ux.dev,
	kpsingh@...nel.org,
	sdf@...ichev.me,
	haoluo@...gle.com,
	jolsa@...nel.org,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: KaFai Wan <mannkafai@...il.com>,
	syzbot+0903f6d7f285e41cdf10@...kaller.appspotmail.com
Subject: [PATCH bpf-next 1/1] bpf: fix WARNING in __bpf_prog_ret0_warn when jit failed

syzkaller reported an issue:

WARNING: CPU: 3 PID: 217 at kernel/bpf/core.c:2357 __bpf_prog_ret0_warn+0xa/0x20 kernel/bpf/core.c:2357
Modules linked in:
CPU: 3 UID: 0 PID: 217 Comm: kworker/u32:6 Not tainted 6.15.0-rc4-syzkaller-00040-g8bac8898fe39 #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: ipv6_addrconf addrconf_dad_work
RIP: 0010:__bpf_prog_ret0_warn+0xa/0x20 kernel/bpf/core.c:2357
RSP: 0018:ffffc900031f6c18 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffc9000006e000 RCX: 1ffff9200000dc06
RDX: ffff8880234ba440 RSI: ffffffff81ca6979 RDI: ffff888031e93040
RBP: ffffc900031f6cb8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88802b61e010
R13: ffff888031e93040 R14: 00000000000000a0 R15: ffff88802c3d4800
FS:  0000000000000000(0000) GS:ffff8880d6ce2000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557b6d2ca8 CR3: 000000002473e000 CR4: 0000000000352ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 bpf_dispatcher_nop_func include/linux/bpf.h:1316 [inline]
 __bpf_prog_run include/linux/filter.h:718 [inline]
 bpf_prog_run include/linux/filter.h:725 [inline]
 cls_bpf_classify+0x74a/0x1110 net/sched/cls_bpf.c:105
 ...

When creating bpf program, 'fp->jit_requested' depends on bpf_jit_enable.
Currently the value of bpf_jit_enable is available from 0 to 2, 0 means use
interpreter and not jit, 1 and 2 means need to jit. When
CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set
to 1, when it's not set or disabled, we can set bpf_jit_enable via proc.

This issue is triggered because of CONFIG_BPF_JIT_ALWAYS_ON is not set
and bpf_jit_enable is set to 1, causing the arch to attempt JIT the prog,
but jit failed due to FAULT_INJECTION. As a result, incorrectly
treats the program as valid, when the program runs it calls
`__bpf_prog_ret0_warn` and triggers the WARN_ON_ONCE(1).

Reported-by: syzbot+0903f6d7f285e41cdf10@...kaller.appspotmail.com
Closes: https://lore.kernel.org/bpf/6816e34e.a70a0220.254cdc.002c.GAE@google.com
Fixes: fa9dd599b4da ("bpf: get rid of pure_initcall dependency to enable jits")
Signed-off-by: KaFai Wan <mannkafai@...il.com>
---
 kernel/bpf/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index a3e571688421..c20babbf998f 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -2474,7 +2474,7 @@ struct bpf_prog *bpf_prog_select_runtime(struct bpf_prog *fp, int *err)
 	/* In case of BPF to BPF calls, verifier did all the prep
 	 * work with regards to JITing, etc.
 	 */
-	bool jit_needed = false;
+	bool jit_needed = fp->jit_requested;
 
 	if (fp->bpf_func)
 		goto finalize;
-- 
2.43.0