Commit 75672dda authored Jun 25, 2019 by Jiong Wang Committed by Daniel Borkmann Jun 26, 2019

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: 2dc6b100 ("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>

parent 6c6874f4

kernel/bpf/core.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;

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