Re: [PATCH bpf] bpf, arm64: Fix bpf trampoline instruction endianness

[Daniel Borkmann]

On 8/9/22 12:33 PM, Jean-Philippe Brucker wrote:
> [+ arm64 maintainers]
>
> On Mon, Aug 08, 2022 at 12:07:35AM -0400, Xu Kuohai wrote:
> > The sparse tool complains as follows:
> >
> > arch/arm64/net/bpf_jit_comp.c:1684:16:
> > 	warning: incorrect type in assignment (different base types)
> > arch/arm64/net/bpf_jit_comp.c:1684:16:
> > 	expected unsigned int [usertype] *branch
> > arch/arm64/net/bpf_jit_comp.c:1684:16:
> > 	got restricted __le32 [usertype] *
> > arch/arm64/net/bpf_jit_comp.c:1700:52:
> > 	error: subtraction of different types can't work (different base
> > 	types)
> > arch/arm64/net/bpf_jit_comp.c:1734:29:
> > 	warning: incorrect type in assignment (different base types)
> > arch/arm64/net/bpf_jit_comp.c:1734:29:
> > 	expected unsigned int [usertype] *
> > arch/arm64/net/bpf_jit_comp.c:1734:29:
> > 	got restricted __le32 [usertype] *
> > arch/arm64/net/bpf_jit_comp.c:1918:52:
> > 	error: subtraction of different types can't work (different base
> > 	types)
> >
> > This is because the variable branch in function invoke_bpf_prog and the
> > variable branches in function prepare_trampoline are defined as type
> > u32 *, which conflicts with ctx->image's type __le32 *, so sparse complains
> > when assignment or arithmetic operation are performed on these two
> > variables and ctx->image.
> >
> > Since arm64 instructions are always little-endian, change the type of
> > these two variables to __le32 * and call cpu_to_le32 to convert
> > instruction to little-endian before writing it to memory.
> >
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Fixes: efc9909fdce0 ("bpf, arm64: Add bpf trampoline for arm64")
> > Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
>
> Reviewed-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>

Applied, thanks! Also added small note that this is in line with emit() as well.