linux-kernel - [PATCH v3 2/2] selftests/bpf: Add test for BPF_NEG alu on CONST_PTR_TO

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Message-ID: <20251001095613.267475-3-listout@listout.xyz>
Date: Wed,  1 Oct 2025 15:26:13 +0530
From: Brahmajit Das <listout@...tout.xyz>
To: syzbot+d36d5ae81e1b0a53ef58@...kaller.appspotmail.com
Cc: andrii@...nel.org,
	ast@...nel.org,
	bpf@...r.kernel.org,
	daniel@...earbox.net,
	eddyz87@...il.com,
	haoluo@...gle.com,
	john.fastabend@...il.com,
	jolsa@...nel.org,
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	song@...nel.org,
	syzkaller-bugs@...glegroups.com,
	yonghong.song@...ux.dev,
	kafai.wan@...ux.dev
Subject: [PATCH v3 2/2] selftests/bpf: Add test for BPF_NEG alu on CONST_PTR_TO_MAP

From: KaFai Wan <kafai.wan@...ux.dev>

Add a test case for BPF_NEG operation on CONST_PTR_TO_MAP. Tests if
BPF_NEG operation on map_ptr is rejected in unprivileged mode and is a
scalar value and do not trigger Oops in privileged mode.

Signed-off-by: KaFai Wan <kafai.wan@...ux.dev>
---
 .../bpf/progs/verifier_value_illegal_alu.c     | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c b/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
index a9ab37d3b9e2..dcaab61a11a0 100644
--- a/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
+++ b/tools/testing/selftests/bpf/progs/verifier_value_illegal_alu.c
@@ -146,6 +146,24 @@ l0_%=:	exit;						\
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("map_ptr illegal alu op, map_ptr = -map_ptr")
+__failure __msg("R0 invalid mem access 'scalar'")
+__failure_unpriv __msg_unpriv("R0 pointer arithmetic prohibited")
+__flag(BPF_F_ANY_ALIGNMENT)
+__naked void map_ptr_illegal_alu_op(void)
+{
+	asm volatile ("					\
+	r0 = %[map_hash_48b] ll;			\
+	r0 = -r0;					\
+	r1 = 22;					\
+	*(u64*)(r0 + 0) = r1;				\
+	exit;						\
+"	:
+	: __imm_addr(map_hash_48b)
+	: __clobber_all);
+}
+
 SEC("flow_dissector")
 __description("flow_keys illegal alu op with variable offset")
 __failure __msg("R7 pointer arithmetic on flow_keys prohibited")
-- 
2.51.0