On 6/12/23 7:52 PM, 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.
Please make it clear that there are no bugs in the existing code
since for each argument, a type case will happen like
(parameter_type)ctx[stack_slot]
where ctx[] is an u64 type array. The compiler will generate
correct code to do type casting so garbage value will not impact
the final result. But indeed, uniformly
do save/restore with BPF_DW size can simplify code.
Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
---
arch/x86/net/bpf_jit_comp.c | 35 ++++++-----------------------------
1 file changed, 6 insertions(+), 29 deletions(-)
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 1056bbf55b17..a407fbbffecd 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1860,57 +1860,34 @@ st: if (is_imm8(insn->off))
static void save_regs(const struct btf_func_model *m, u8 **prog, int nr_regs,
int stack_size)
{
- int i, j, arg_size;
- bool next_same_struct = false;
+ int i;
/* Store function arguments to stack.
* For a function that accepts two pointers the sequence will be:
* mov QWORD PTR [rbp-0x10],rdi
* mov QWORD PTR [rbp-0x8],rsi
*/
- for (i = 0, j = 0; i < min(nr_regs, 6); i++) {
- /* The arg_size is at most 16 bytes, enforced by the verifier. */
- arg_size = m->arg_size[j];
- if (arg_size > 8) {
- arg_size = 8;
- next_same_struct = !next_same_struct;
- }
-
- emit_stx(prog, bytes_to_bpf_size(arg_size),
- BPF_REG_FP,
+ for (i = 0; i < min(nr_regs, 6); i++)
+ emit_stx(prog, BPF_DW, BPF_REG_FP,
i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
-(stack_size - i * 8));
-
- j = next_same_struct ? j : j + 1;
- }
}
[...]
