bpf: fix BPF_ALU32 | BPF_ARSH on BE arches

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 <[email protected]>
Reviewed-by: Jakub Kicinski <[email protected]>
Reviewed-by: Quentin Monnet <[email protected]>
Signed-off-by: Jiong Wang <[email protected]>
Acked-by: Song Liu <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 080e2bb644cc..f2148db91439 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1364,10 +1364,10 @@ 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;