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Tue, 29 Apr 2025 07:16:22 -0700 (PDT) Received: from mail.gmail.com ([2a04:ee41:4:b2de:1ac0:4dff:fe0f:3782]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ace6edb0becsm779464966b.167.2025.04.29.07.16.21 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Apr 2025 07:16:21 -0700 (PDT) Date: Tue, 29 Apr 2025 14:21:11 +0000 From: Anton Protopopov To: bpf@vger.kernel.org Subject: Re: [PATCH v1 bpf-next] bpf: fix uninitialized values in BPF_{CORE,PROBE}_READ Message-ID: References: <20250429130809.1811713-1-a.s.protopopov@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250429130809.1811713-1-a.s.protopopov@gmail.com> On 25/04/29 01:08PM, Anton Protopopov wrote: > With the latest LLVM bpf selftests build will fail: > > progs/profiler.inc.h:710:31: error: default initialization of an object of type 'typeof ((parent_task)->real_cred->uid.val)' (aka 'const unsigned int') leaves the object uninitialized and is incompatible with C++ [-Werror,-Wdefault-const-init-unsafe] > 710 | proc_exec_data->parent_uid = BPF_CORE_READ(parent_task, real_cred, uid.val); > | ^ > tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:520:35: note: expanded from macro 'BPF_CORE_READ' > 520 | ___type((src), a, ##__VA_ARGS__) __r; \ > | ^ > > Fix this by declaring __r to be an array of __u8 of a proper size. > > Fixes: 792001f4f7aa ("libbpf: Add user-space variants of BPF_CORE_READ() family of macros") > Fixes: a4b09a9ef945 ("libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family") > Signed-off-by: Anton Protopopov > --- > tools/lib/bpf/bpf_core_read.h | 24 ++++++++++++------------ > 1 file changed, 12 insertions(+), 12 deletions(-) > > diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h > index c0e13cdf9660..be556ccdc002 100644 > --- a/tools/lib/bpf/bpf_core_read.h > +++ b/tools/lib/bpf/bpf_core_read.h > @@ -517,9 +517,9 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak; > * than enough for any practical purpose. > */ > #define BPF_CORE_READ(src, a, ...) ({ \ > - ___type((src), a, ##__VA_ARGS__) __r; \ > - BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \ > - __r; \ > + __u8 __r[sizeof(___type((src), a, ##__VA_ARGS__))]; \ > + BPF_CORE_READ_INTO(__r, (src), a, ##__VA_ARGS__); \ And, of course, this breaks things. The line above should have stayed with &. I will send v2. > + *(___type((src), a, ##__VA_ARGS__) *)__r; \ > }) > > /* > @@ -533,16 +533,16 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak; > * input argument. > */ > #define BPF_CORE_READ_USER(src, a, ...) ({ \ > - ___type((src), a, ##__VA_ARGS__) __r; \ > - BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \ > - __r; \ > + __u8 __r[sizeof(___type((src), a, ##__VA_ARGS__))]; \ > + BPF_CORE_READ_USER_INTO(__r, (src), a, ##__VA_ARGS__); \ > + *(___type((src), a, ##__VA_ARGS__) *)__r; \ > }) > > /* Non-CO-RE variant of BPF_CORE_READ() */ > #define BPF_PROBE_READ(src, a, ...) ({ \ > - ___type((src), a, ##__VA_ARGS__) __r; \ > - BPF_PROBE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \ > - __r; \ > + __u8 __r[sizeof(___type((src), a, ##__VA_ARGS__))]; \ > + BPF_PROBE_READ_INTO(__r, (src), a, ##__VA_ARGS__); \ > + *(___type((src), a, ##__VA_ARGS__) *)__r; \ > }) > > /* > @@ -552,9 +552,9 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak; > * not restricted to kernel types only. > */ > #define BPF_PROBE_READ_USER(src, a, ...) ({ \ > - ___type((src), a, ##__VA_ARGS__) __r; \ > - BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \ > - __r; \ > + __u8 __r[sizeof(___type((src), a, ##__VA_ARGS__))]; \ > + BPF_PROBE_READ_USER_INTO(__r, (src), a, ##__VA_ARGS__); \ > + *(___type((src), a, ##__VA_ARGS__) *)__r; \ > }) > > #endif > -- > 2.34.1 >