From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
"davem@davemloft.net" <davem@davemloft.net>,
"daniel@iogearbox.net" <daniel@iogearbox.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 1/6] libbpf: Sanitize BTF_KIND_FUNC linkage
Date: Wed, 8 Jan 2020 12:12:57 -0800 [thread overview]
Message-ID: <20200108201256.2wtawgl3e4d4dkka@ast-mbp> (raw)
In-Reply-To: <d2fab68b-cd03-7a15-e353-c614f6079b89@fb.com>
On Wed, Jan 08, 2020 at 06:57:18PM +0000, Yonghong Song wrote:
>
>
> On 1/7/20 11:25 PM, Alexei Starovoitov wrote:
> > In case kernel doesn't support static/global/extern liknage of BTF_KIND_FUNC
> > sanitize BTF produced by llvm.
> >
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > ---
> > tools/include/uapi/linux/btf.h | 6 ++++++
> > tools/lib/bpf/libbpf.c | 35 +++++++++++++++++++++++++++++++++-
> > 2 files changed, 40 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/include/uapi/linux/btf.h b/tools/include/uapi/linux/btf.h
> > index 1a2898c482ee..5a667107ad2c 100644
> > --- a/tools/include/uapi/linux/btf.h
> > +++ b/tools/include/uapi/linux/btf.h
> > @@ -146,6 +146,12 @@ enum {
> > BTF_VAR_GLOBAL_EXTERN = 2,
> > };
> >
> > +enum btf_func_linkage {
> > + BTF_FUNC_STATIC = 0,
> > + BTF_FUNC_GLOBAL = 1,
> > + BTF_FUNC_EXTERN = 2,
> > +};
> > +
> > /* BTF_KIND_VAR is followed by a single "struct btf_var" to describe
> > * additional information related to the variable such as its linkage.
> > */
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 7513165b104f..f72b3ed6c34b 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -166,6 +166,8 @@ struct bpf_capabilities {
> > __u32 btf_datasec:1;
> > /* BPF_F_MMAPABLE is supported for arrays */
> > __u32 array_mmap:1;
> > + /* static/global/extern is supported for BTF_KIND_FUNC */
> > + __u32 btf_func_linkage:1;
> > };
> >
> > enum reloc_type {
> > @@ -1817,13 +1819,14 @@ static bool section_have_execinstr(struct bpf_object *obj, int idx)
> >
> > static void bpf_object__sanitize_btf(struct bpf_object *obj)
> > {
> > + bool has_func_linkage = obj->caps.btf_func_linkage;
> > bool has_datasec = obj->caps.btf_datasec;
> > bool has_func = obj->caps.btf_func;
> > struct btf *btf = obj->btf;
> > struct btf_type *t;
> > int i, j, vlen;
> >
> > - if (!obj->btf || (has_func && has_datasec))
> > + if (!obj->btf || (has_func && has_datasec && has_func_linkage))
> > return;
> >
> > for (i = 1; i <= btf__get_nr_types(btf); i++) {
> > @@ -1871,6 +1874,9 @@ static void bpf_object__sanitize_btf(struct bpf_object *obj)
> > } else if (!has_func && btf_is_func(t)) {
> > /* replace FUNC with TYPEDEF */
> > t->info = BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0);
> > + } else if (!has_func_linkage && btf_is_func(t)) {
> > + /* replace BTF_FUNC_GLOBAL with BTF_FUNC_STATIC */
> > + t->info = BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0);
>
> The comment says we only sanitize BTF_FUNC_GLOBAL here.
> Actually, it also sanitize BTF_FUNC_EXTERN.
>
> Currently, in kernel/bpf/btf.c, we have
> static int btf_check_all_types(struct btf_verifier_env *env)
> {
> ...
> if (btf_type_is_func(t)) {
> err = btf_func_check(env, t);
> if (err)
> return err;
> }
> ...
> }
>
> btf_func_check() will ensure func btf_type->type is a func_proto
> and all arguments of func_proto has a name except void which is
> considered as varg.
>
> For extern function, the argument name is lost in llvm/clang.
>
> -bash-4.4$ cat test.c
>
> extern int foo(int a);
> int test() { return foo(5); }
> -bash-4.4$
> -bash-4.4$ clang -target bpf -O2 -g -S -emit-llvm test.c
>
> !2 = !{}
> !4 = !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !5,
> flags: DIFlagPrototyped, spFlags: DISPFlagOptimized, retainedNodes: !2)
> !5 = !DISubroutineType(types: !6)
> !6 = !{!7, !7}
> !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
>
> To avoid kernel complaints, we need to sanitize in a different way.
> For example extern BTF_KIND_FUNC could be rewritten to a
> BTF_KIND_PTR to void.
Good point. I'll reword the comment and rename the test to btf_func_global,
so it probes kernel for KIND_GLOBAL only and santizes only that bit.
KIND_EXTERN sanitization is to be done later. Separate libbpf and kernel patches.
next prev parent reply other threads:[~2020-01-08 20:13 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-08 7:25 [PATCH bpf-next 0/6] bpf: Introduce global functions Alexei Starovoitov
2020-01-08 7:25 ` [PATCH bpf-next 1/6] libbpf: Sanitize BTF_KIND_FUNC linkage Alexei Starovoitov
2020-01-08 17:35 ` Song Liu
2020-01-08 18:57 ` Yonghong Song
2020-01-08 20:12 ` Alexei Starovoitov [this message]
2020-01-08 7:25 ` [PATCH bpf-next 2/6] libbpf: Collect static vs global info about functions Alexei Starovoitov
2020-01-08 10:25 ` Toke Høiland-Jørgensen
2020-01-08 16:25 ` Yonghong Song
2020-01-09 8:50 ` Toke Høiland-Jørgensen
2020-01-08 17:57 ` Song Liu
2020-01-08 20:10 ` Alexei Starovoitov
2020-01-08 7:25 ` [PATCH bpf-next 3/6] bpf: Introduce function-by-function verification Alexei Starovoitov
2020-01-08 10:28 ` Toke Høiland-Jørgensen
2020-01-08 20:06 ` Alexei Starovoitov
2020-01-09 8:57 ` Toke Høiland-Jørgensen
2020-01-09 23:03 ` Alexei Starovoitov
2020-01-10 10:08 ` Toke Høiland-Jørgensen
2020-01-08 19:10 ` Song Liu
2020-01-08 20:20 ` Alexei Starovoitov
2020-01-08 21:24 ` Song Liu
2020-01-08 23:05 ` Alexei Starovoitov
2020-01-14 23:39 ` Stanislav Fomichev
2020-01-14 23:56 ` Andrii Nakryiko
2020-01-15 0:44 ` Stanislav Fomichev
2020-01-08 7:25 ` [PATCH bpf-next 4/6] selftests/bpf: Add fexit-to-skb test for global funcs Alexei Starovoitov
2020-01-08 19:15 ` Song Liu
2020-01-08 7:25 ` [PATCH bpf-next 5/6] selftests/bpf: Add a test for a large global function Alexei Starovoitov
2020-01-08 19:16 ` Song Liu
2020-01-08 19:17 ` Song Liu
2020-01-08 7:25 ` [PATCH bpf-next 6/6] selftests/bpf: Modify a test to check global functions Alexei Starovoitov
2020-01-08 19:18 ` Song Liu
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