From: Menglong Dong <[email protected]>
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.
Signed-off-by: Menglong Dong <[email protected]>
---
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;
- }
}
static void restore_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;
/* Restore function arguments from stack.
* For a function that accepts two pointers the sequence will be:
* EMIT4(0x48, 0x8B, 0x7D, 0xF0); mov rdi,QWORD PTR [rbp-0x10]
* EMIT4(0x48, 0x8B, 0x75, 0xF8); mov rsi,QWORD PTR [rbp-0x8]
*/
- 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_ldx(prog, bytes_to_bpf_size(arg_size),
+ for (i = 0; i < min(nr_regs, 6); i++)
+ emit_ldx(prog, BPF_DW,
i == 5 ? X86_REG_R9 : BPF_REG_1 + i,
BPF_REG_FP,
-(stack_size - i * 8));
-
- j = next_same_struct ? j : j + 1;
- }
}
static int invoke_bpf_prog(const struct btf_func_model *m, u8 **pprog,
--
2.40.1
On 6/12/23 7:52 PM, [email protected] wrote:
> From: Menglong Dong <[email protected]>
>
> 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 <[email protected]>
Acked-by: Yonghong Song <[email protected]>
> ---
> 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;
> - }
> }
>
[...]
On Mon, Jun 19, 2023 at 6:52 AM Yonghong Song <[email protected]> wrote:
>
>
>
> On 6/12/23 7:52 PM, [email protected] wrote:
> > From: Menglong Dong <[email protected]>
> >
> > 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.
>
Yeah, this is to prepare for the next commit and no bugs
in the existing code. I'll make it clear in the commit log in
the next version.
Thanks!
Menglong Dong
> >
> > Signed-off-by: Menglong Dong <[email protected]>
>
> Acked-by: Yonghong Song <[email protected]>
>
> > ---
> > 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;
> > - }
> > }
> >
> [...]