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Mon, 15 Apr 2024 09:20:55 -0700 (PDT) Date: Mon, 15 Apr 2024 18:20:45 +0200 In-Reply-To: <20240415162041.2491523-5-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240415162041.2491523-5-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=2668; i=ardb@kernel.org; h=from:subject; bh=r5HeLLaiZQAh9QWD51AJtOhyniRpUOwKFejoofTylQw=; b=owGbwMvMwCFmkMcZplerG8N4Wi2JIU02+M7jo28Fo36cTxHbcXHZE5f2CWJ3C1mm+lxU4Ww4e rA53Ni2o5SFQYyDQVZMkUVg9t93O09PlKp1niULM4eVCWQIAxenAExEJZzhr8CHbGvGxUIxhboC bnceXbJce7Hx7oOShfraG7sD76299I2RoaeEq++zoZeohsI2xcNPzws8dNRcm/ZAlknm1+JvGV3 ejAA= X-Mailer: git-send-email 2.44.0.683.g7961c838ac-goog Message-ID: <20240415162041.2491523-8-ardb+git@google.com> Subject: [PATCH v4 3/3] btf: Avoid weak external references From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: Ard Biesheuvel , Masahiro Yamada , Arnd Bergmann , Martin KaFai Lau , linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, Andrii Nakryiko , Jiri Olsa , Jiri Olsa Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Ard Biesheuvel If the BTF code is enabled in the build configuration, the start/stop BTF markers are guaranteed to exist. Only when CONFIG_DEBUG_INFO_BTF=3Dn, the references in btf_parse_vmlinux() will remain unsatisfied, relying on the weak linkage of the external references to avoid breaking the build. Avoid GOT based relocations to these markers in the final executable by dropping the weak attribute and instead, make btf_parse_vmlinux() return ERR_PTR(-ENOENT) directly if CONFIG_DEBUG_INFO_BTF is not enabled to begin with. The compiler will drop any subsequent references to __start_BTF and __stop_BTF in that case, allowing the link to succeed. Note that Clang will notice that taking the address of __start_BTF can no longer yield NULL, so testing for that condition becomes unnecessary. Acked-by: Andrii Nakryiko Acked-by: Arnd Bergmann Acked-by: Jiri Olsa Signed-off-by: Ard Biesheuvel --- kernel/bpf/btf.c | 7 +++++-- kernel/bpf/sysfs_btf.c | 6 +++--- 2 files changed, 8 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index 90c4a32d89ff..6d46cee47ae3 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -5642,8 +5642,8 @@ static struct btf *btf_parse(const union bpf_attr *at= tr, bpfptr_t uattr, u32 uat return ERR_PTR(err); } =20 -extern char __weak __start_BTF[]; -extern char __weak __stop_BTF[]; +extern char __start_BTF[]; +extern char __stop_BTF[]; extern struct btf *btf_vmlinux; =20 #define BPF_MAP_TYPE(_id, _ops) @@ -5971,6 +5971,9 @@ struct btf *btf_parse_vmlinux(void) struct btf *btf =3D NULL; int err; =20 + if (!IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) + return ERR_PTR(-ENOENT); + env =3D kzalloc(sizeof(*env), GFP_KERNEL | __GFP_NOWARN); if (!env) return ERR_PTR(-ENOMEM); diff --git a/kernel/bpf/sysfs_btf.c b/kernel/bpf/sysfs_btf.c index ef6911aee3bb..fedb54c94cdb 100644 --- a/kernel/bpf/sysfs_btf.c +++ b/kernel/bpf/sysfs_btf.c @@ -9,8 +9,8 @@ #include =20 /* See scripts/link-vmlinux.sh, gen_btf() func for details */ -extern char __weak __start_BTF[]; -extern char __weak __stop_BTF[]; +extern char __start_BTF[]; +extern char __stop_BTF[]; =20 static ssize_t btf_vmlinux_read(struct file *file, struct kobject *kobj, @@ -32,7 +32,7 @@ static int __init btf_vmlinux_init(void) { bin_attr_btf_vmlinux.size =3D __stop_BTF - __start_BTF; =20 - if (!__start_BTF || bin_attr_btf_vmlinux.size =3D=3D 0) + if (bin_attr_btf_vmlinux.size =3D=3D 0) return 0; =20 btf_kobj =3D kobject_create_and_add("btf", kernel_kobj); --=20 2.44.0.683.g7961c838ac-goog