[PATCH AUTOSEL 5.1 156/219] bpf: fix BPF_ALU32 | BPF_ARSH on BE arches

Sasha Levin
2019-07-15T14:13:24Z

From: Jiong Wang <jiong.wang@netronome.com>

[ 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>
---
kernel/bpf/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 06ba9c5f156b..932fd3fa5a5a 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1367,10 +1367,10 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack)
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;
--
2.20.1