bpf: fix BPF_ALU32 | BPF_ARSH on BE arches

[ Upstream commit 75672dda27bd00109a84cd975c17949ad9c45663 ]

Yauheni reported the following code do not work correctly on BE arches:

       ALU_ARSH_X:
               DST = (u64) (u32) ((*(s32 *) &DST) >> SRC);
               CONT;
       ALU_ARSH_K:
               DST = (u64) (u32) ((*(s32 *) &DST) >> IMM);
               CONT;

and are causing failure of test_verifier test 'arsh32 on imm 2' on BE
arches.

The code is taking address and interpreting memory directly, so is not
endianness neutral. We should instead perform standard C type casting on
the variable. A u64 to s32 conversion will drop the high 32-bit and reserve
the low 32-bit as signed integer, this is all we want.

Fixes: 2dc6b100f928 ("bpf: interpreter support BPF_ALU | BPF_ARSH")
Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Jiong Wang <jiong.wang@netronome.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 06ba9c5f156b2733a35be81fa26bdea113e5a5d7..932fd3fa5a5ad6831f0eda2310680a79d319fa7d 100644 (file)
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1367,10 +1367,10 @@ select_insn:
                insn++;
                CONT;
        ALU_ARSH_X:
-               DST = (u64) (u32) ((*(s32 *) &DST) >> SRC);
+               DST = (u64) (u32) (((s32) DST) >> SRC);
                CONT;
        ALU_ARSH_K:
-               DST = (u64) (u32) ((*(s32 *) &DST) >> IMM);
+               DST = (u64) (u32) (((s32) DST) >> IMM);
                CONT;
        ALU64_ARSH_X:
                (*(s64 *) &DST) >>= SRC;