netdev - [PATCH bpf-next v3 06/11] bpf: Fix compare error in function retval_range

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Message-Id: <20240411122752.2873562-7-xukuohai@huaweicloud.com>
Date: Thu, 11 Apr 2024 20:27:47 +0800
From: Xu Kuohai <xukuohai@...weicloud.com>
To: bpf@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-kselftest@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Brendan Jackman <jackmanb@...omium.org>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E . Hallyn" <serge@...lyn.com>,
	Khadija Kamran <kamrankhadijadj@...il.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	John Johansen <john.johansen@...onical.com>,
	Lukas Bulwahn <lukas.bulwahn@...il.com>,
	Roberto Sassu <roberto.sassu@...wei.com>,
	Shung-Hsi Yu <shung-hsi.yu@...e.com>
Subject: [PATCH bpf-next v3 06/11] bpf: Fix compare error in function retval_range_within

From: Xu Kuohai <xukuohai@...wei.com>

After checking lsm hook return range in verifier, the test case
"test_progs -t test_lsm" failed, and the failure log says:

libbpf: prog 'test_int_hook': BPF program load failed: Invalid argument
libbpf: prog 'test_int_hook': -- BEGIN PROG LOAD LOG --
0: R1=ctx() R10=fp0
; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
0: (79) r0 = *(u64 *)(r1 +24)         ; R0_w=scalar(smin=smin32=-4095,smax=smax32=0) R1=ctx()

[...]

24: (b4) w0 = -1                      ; R0_w=0xffffffff
; int BPF_PROG(test_int_hook, struct vm_area_struct *vma, @ lsm.c:89
25: (95) exit
At program exit the register R0 has smin=4294967295 smax=4294967295 should have been in [-4095, 0]

It can be seen that instruction "w0 = -1" zero extended -1 to 64-bit
register r0, setting both smin and smax values of r0 to 4294967295.
This resulted in a false reject when r0 was checked with range [-4095, 0].

Given bpf_retval_range is a 32-bit range, this patch fixes it by
changing the compare between r0 and return range from 64-bit
operation to 32-bit operation.

Fixes: 8fa4ecd49b81 ("bpf: enforce exact retval range on subprog/callback exit")
Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
---
 kernel/bpf/verifier.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 05c7c5f2bec0..5393d576c76f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9879,7 +9879,7 @@ static bool in_rbtree_lock_required_cb(struct bpf_verifier_env *env)
 
 static bool retval_range_within(struct bpf_retval_range range, const struct bpf_reg_state *reg)
 {
-	return range.minval <= reg->smin_value && reg->smax_value <= range.maxval;
+	return range.minval <= reg->s32_min_value && reg->s32_max_value <= range.maxval;
 }
 
 static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
-- 
2.30.2