On Wed, Jun 07, 2023 at 08:59:10PM +0800, menglong8.dong@xxxxxxxxx wrote:
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
>
> There are garbage values in upper bytes when we store the arguments
> into stack in save_regs() if the size of the argument less then 8.
>
> As we already reserve 8 byte for the arguments in regs and stack,
> it is ok to store/restore the regs in BPF_DW size. Then, the garbage
> values in upper bytes will be cleaned.
>
> Reviewed-by: Jiang Biao <benbjiang@xxxxxxxxxxx>
> Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 19 ++++++-------------
> 1 file changed, 6 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 413b986b5afd..e9bc0b50656b 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -1878,20 +1878,16 @@ static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
>
> if (i <= 5) {
> /* copy function arguments from regs into stack */
> - emit_stx(prog, bytes_to_bpf_size(arg_size),
> - BPF_REG_FP,
> + emit_stx(prog, BPF_DW, BPF_REG_FP,
> i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
> -(stack_size - i * 8));
This is ok,
> } else {
> /* copy function arguments from origin stack frame
> * into current stack frame.
> */
> - emit_ldx(prog, bytes_to_bpf_size(arg_size),
> - BPF_REG_0, BPF_REG_FP,
> + emit_ldx(prog, BPF_DW, BPF_REG_0, BPF_REG_FP,
> (i - 6) * 8 + 0x18);
> - emit_stx(prog, bytes_to_bpf_size(arg_size),
> - BPF_REG_FP,
> - BPF_REG_0,
> + emit_stx(prog, BPF_DW, BPF_REG_FP, BPF_REG_0,
> -(stack_size - i * 8));
But this is not.
See https://godbolt.org/z/qW17f6cYe
mov dword ptr [rsp], 6
the compiler will store 32-bit only. The upper 32-bit are still garbage.
> }
>
> @@ -1918,7 +1914,7 @@ static void restore_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
> next_same_struct = !next_same_struct;
> }
>
> - emit_ldx(prog, bytes_to_bpf_size(arg_size),
> + emit_ldx(prog, BPF_DW,
> i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
> BPF_REG_FP,
> -(stack_size - i * 8));
> @@ -1949,12 +1945,9 @@ static void prepare_origin_stack(const struct btf_func_model *m, u8 **prog,
> }
>
> if (i > 5) {
> - emit_ldx(prog, bytes_to_bpf_size(arg_size),
> - BPF_REG_0, BPF_REG_FP,
> + emit_ldx(prog, BPF_DW, BPF_REG_0, BPF_REG_FP,
> (i - 6) * 8 + 0x18);
> - emit_stx(prog, bytes_to_bpf_size(arg_size),
> - BPF_REG_FP,
> - BPF_REG_0,
> + emit_stx(prog, BPF_DW, BPF_REG_FP, BPF_REG_0,
> -(stack_size - (i - 6) * 8));
> }
>
> --
> 2.40.1
>
