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Groups > linux.kernel > #1279758
| From | Wang Nan <wangnan0@huawei.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH] tools lib bpf: Fetch map names from correct strtab |
| Date | 2015-11-30 11:40 +0100 |
| Message-ID | <qAu2e-2mA-7@gated-at.bofh.it> (permalink) |
| References | <qAtfP-1R8-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Namhyung Kim pointed out a potential problem in original code that it
fetches names of maps from section header string table, which is used
to store section names.
Original code doesn't cause error because of a LLVM behavior that, it
combines shstrtab into strtab. For example:
$ echo 'int func() {return 0;}' | x86_64-oe-linux-clang -x c -o temp.o -c -
$ readelf -h ./temp.o
ELF Header:
Magic: 7f 45 4c 46 02 01 01 03 00 00 00 00 00 00 00 00
...
Section header string table index: 1
$ readelf -S ./temp.o
There are 10 section headers, starting at offset 0x288:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .strtab STRTAB 0000000000000000 00000230
0000000000000051 0000000000000000 0 0 1
...
$ readelf -p .strtab ./temp.o
String dump of section '.strtab':
[ 1] .text
[ 7] .comment
[ 10] .bss
[ 15] .note.GNU-stack
[ 25] .rela.eh_frame
[ 34] func
[ 39] .strtab
[ 41] .symtab
[ 49] .data
[ 4f] -
$ readelf -p .shstrtab ./temp.o
readelf: Warning: Section '.shstrtab' was not dumped because it does not exist!
Where, 'section header string table index' points to '.strtab', and
symbol names are also stored there.
However, in case of gcc:
$ echo 'int func() {return 0;}' | gcc -x c -o temp.o -c -
$ readelf -p .shstrtab ./temp.o
String dump of section '.shstrtab':
[ 1] .symtab
[ 9] .strtab
[ 11] .shstrtab
[ 1b] .text
[ 21] .data
[ 27] .bss
[ 2c] .comment
[ 35] .note.GNU-stack
[ 45] .rela.eh_frame
$ readelf -p .strtab ./temp.o
String dump of section '.strtab':
[ 1] func
They are separated sections.
Although original code doesn't cause error, we'd better use canonical
method for fetching symbol names to avoid potential behavior changing.
This patch learns from readelf's code, fetches string from sh_link
of .symbol section.
Reported-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/lib/bpf/libbpf.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 16485ab..8334a5a 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -195,6 +195,7 @@ struct bpf_object {
Elf *elf;
GElf_Ehdr ehdr;
Elf_Data *symbols;
+ size_t strtabidx;
struct {
GElf_Shdr shdr;
Elf_Data *data;
@@ -547,7 +548,7 @@ bpf_object__init_maps_name(struct bpf_object *obj, int maps_shndx)
continue;
map_name = elf_strptr(obj->efile.elf,
- obj->efile.ehdr.e_shstrndx,
+ obj->efile.strtabidx,
sym.st_name);
map_idx = sym.st_value / sizeof(struct bpf_map_def);
if (map_idx >= obj->nr_maps) {
@@ -630,8 +631,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
pr_warning("bpf: multiple SYMTAB in %s\n",
obj->path);
err = -LIBBPF_ERRNO__FORMAT;
- } else
+ } else {
obj->efile.symbols = data;
+ obj->efile.strtabidx = sh.sh_link;
+ }
} else if ((sh.sh_type == SHT_PROGBITS) &&
(sh.sh_flags & SHF_EXECINSTR) &&
(data->d_size > 0)) {
@@ -667,6 +670,10 @@ static int bpf_object__elf_collect(struct bpf_object *obj)
goto out;
}
+ if (!obj->efile.strtabidx || obj->efile.strtabidx >= idx) {
+ pr_warning("Corrupted ELF file: index of strtab invalid\n");
+ return LIBBPF_ERRNO__FORMAT;
+ }
if (maps_shndx >= 0)
err = bpf_object__init_maps_name(obj, maps_shndx);
out:
--
1.8.3.4
--
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[PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file Wang Nan <wangnan0@huawei.com> - 2015-11-27 09:50 +0100
[tip:perf/core] tools lib bpf: Extract and collect map names from BPF object file tip-bot for Wang Nan <tipbot@zytor.com> - 2015-11-29 09:00 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file Namhyung Kim <namhyung@kernel.org> - 2015-11-29 17:20 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-30 06:10 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file Namhyung Kim <namhyung@kernel.org> - 2015-11-30 10:00 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-30 10:30 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file Namhyung Kim <namhyung@gmail.com> - 2015-11-30 10:50 +0100
Re: [PATCH v2 02/13] bpf tools: Extract and collect map names from BPF object file "Wangnan (F)" <wangnan0@huawei.com> - 2015-11-30 10:50 +0100
[PATCH] tools lib bpf: Fetch map names from correct strtab Wang Nan <wangnan0@huawei.com> - 2015-11-30 11:40 +0100
Re: [PATCH] tools lib bpf: Fetch map names from correct strtab Namhyung Kim <namhyung@kernel.org> - 2015-11-30 12:30 +0100
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