On Thu, Jun 8, 2023 at 4:03 AM Alexei Starovoitov alexei.starovoitov@gmail.com wrote:
On Wed, Jun 07, 2023 at 08:59:10PM +0800, menglong8.dong@gmail.com wrote:
From: Menglong Dong imagedong@tencent.com
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@tencent.com Signed-off-by: Menglong Dong imagedong@tencent.com
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.
Enn......I didn't expect this case, and it seems that this only happens on clang. With gcc, "push 6" is used.
I haven't found a solution for this case, and it seems not worth it to add an extra insn to clean the garbage values.
Does anyone have any ideas here?
Thanks! Menglong Dong
}@@ -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