Re: [PATCH 2/2] perf bpf: Check relocation target section

From: Wangnan (F)
Date: Sun Jan 24 2016 - 20:57:36 EST




On 2016/1/23 1:11, Alexei Starovoitov wrote:
On Fri, Jan 22, 2016 at 09:27:21AM +0000, Wang Nan wrote:
Libbpf should check target section before doing relocation to ensure
the relocation is correct. If not, a bug in LLVM causes error. See [1].
Also, if an incorrect BPF script uses both global variable and
map, global variable whould be treated as map and be relocated
without error.

This patch saves id of map section into obj->efile and compare
target section of a relocation symbol against it during relocation.
...
[1] https://llvm.org/bugs/show_bug.cgi?id=26243
...
Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
+ if (sym.st_shndx != maps_shndx) {
+ pr_warning("Program '%s' contains non-map related relo data pointing to section %u\n",
+ prog->section_name, sym.st_shndx);
+ return -LIBBPF_ERRNO__RELOC;
+ }
May be 'pr_err' instead of 'pr_warning', since such program will fail
to load by kernel anyway.

Libbpf doesn't issue pr_error even in fatal exception because it doesn't define
pr_err at all. It reports error code and let perf deal with error.

Thank you.

Looks good otherwise.
Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>