Re: [PATCH bpf-next 1/6] libbpf: Sanitize BTF_KIND_FUNC linkage
From: Yonghong Song <hidden>
Date: 2020-01-08 18:57:34
Also in:
bpf
On 1/7/20 11:25 PM, Alexei Starovoitov wrote:
quoted hunk ↗ jump to hunk
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.
quoted hunk ↗ jump to hunk
} } }@@ -2804,6 +2810,32 @@ static int bpf_object__probe_btf_func(struct bpf_object *obj) return 0; } +static int bpf_object__probe_btf_func_linkage(struct bpf_object *obj) +{ + static const char strs[] = "\0int\0x\0a"; + /* static void x(int a) {} */ + __u32 types[] = { + /* int */ + BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4), /* [1] */ + /* FUNC_PROTO */ /* [2] */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 0), + BTF_PARAM_ENC(7, 1), + /* FUNC x BTF_FUNC_GLOBAL */ /* [3] */ + BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, 1), 2), + }; + int btf_fd; + + btf_fd = libbpf__load_raw_btf((char *)types, sizeof(types), + strs, sizeof(strs)); + if (btf_fd >= 0) { + obj->caps.btf_func_linkage = 1; + close(btf_fd); + return 1; + } + + return 0; +} + static int bpf_object__probe_btf_datasec(struct bpf_object *obj) { static const char strs[] = "\0x\0.data";@@ -2859,6 +2891,7 @@ bpf_object__probe_caps(struct bpf_object *obj) bpf_object__probe_name, bpf_object__probe_global_data, bpf_object__probe_btf_func, + bpf_object__probe_btf_func_linkage, bpf_object__probe_btf_datasec, bpf_object__probe_array_mmap, };