| Message ID | 20200430213101.135134-6-arnd@arndb.de |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | gcc-10 warning fixes | expand |
On 4/30/20 11:30 PM, Arnd Bergmann wrote: > gcc-10 warns about accesses to zero-length arrays: > > kernel/bpf/core.c: In function 'bpf_patch_insn_single': > cc1: warning: writing 8 bytes into a region of size 0 [-Wstringop-overflow=] > In file included from kernel/bpf/core.c:21: > include/linux/filter.h:550:20: note: at offset 0 to object 'insnsi' with size 0 declared here > 550 | struct bpf_insn insnsi[0]; > | ^~~~~~ > > In this case, we really want to have two flexible-array members, > but that is not possible. Removing the union to make insnsi a > flexible-array member while leaving insns as a zero-length array > fixes the warning, as nothing writes to the other one in that way. > > This trick only works on linux-3.18 or higher, as older versions > had additional members in the union. > > Fixes: 60a3b2253c41 ("net: bpf: make eBPF interpreter images read-only") > Signed-off-by: Arnd Bergmann <arnd@arndb.de> Not pretty but looks okay to me, both have the same offset afterwards in the pahole dump as well. struct bpf_prog { [...] unsigned int (*bpf_func)(const void *, const struct bpf_insn *); /* 48 8 */ struct sock_filter insns[0]; /* 56 0 */ struct bpf_insn insnsi[]; /* 56 0 */ /* size: 56, cachelines: 1, members: 21 */ /* sum members: 50, holes: 1, sum holes: 4 */ /* sum bitfield members: 10 bits, bit holes: 1, sum bit holes: 6 bits */ /* last cacheline: 56 bytes */ }; Applied to bpf-next, thanks!
diff --git a/include/linux/filter.h b/include/linux/filter.h index af37318bb1c5..73d06a39e2d6 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -545,10 +545,8 @@ struct bpf_prog { unsigned int (*bpf_func)(const void *ctx, const struct bpf_insn *insn); /* Instructions for interpreter */ - union { - struct sock_filter insns[0]; - struct bpf_insn insnsi[0]; - }; + struct sock_filter insns[0]; + struct bpf_insn insnsi[]; }; struct sk_filter {
gcc-10 warns about accesses to zero-length arrays: kernel/bpf/core.c: In function 'bpf_patch_insn_single': cc1: warning: writing 8 bytes into a region of size 0 [-Wstringop-overflow=] In file included from kernel/bpf/core.c:21: include/linux/filter.h:550:20: note: at offset 0 to object 'insnsi' with size 0 declared here 550 | struct bpf_insn insnsi[0]; | ^~~~~~ In this case, we really want to have two flexible-array members, but that is not possible. Removing the union to make insnsi a flexible-array member while leaving insns as a zero-length array fixes the warning, as nothing writes to the other one in that way. This trick only works on linux-3.18 or higher, as older versions had additional members in the union. Fixes: 60a3b2253c41 ("net: bpf: make eBPF interpreter images read-only") Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- include/linux/filter.h | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)