Re: [PATCHv4 net-next 07/15] bpf: recognize 64bit immediate loads as consts

[Alexei Starovoitov]

On Thu, Sep 15, 2016 at 08:12:27PM +0100, Jakub Kicinski wrote:
> When running as parser interpret BPF_LD | BPF_IMM | BPF_DW
> instructions as loading CONST_IMM with the value stored
> in imm.  The verifier will continue not recognizing those
> due to concerns about search space/program complexity
> increase.
> 
> Signed-off-by: Jakub Kicinski 
> ---
> v3:
>  - limit to parsers.
> ---
>  kernel/bpf/verifier.c | 14 --
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index d93e78331b90..f5bed7cce08d 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1766,9 +1766,19 @@ static int check_ld_imm(struct bpf_verifier_env *env, 
> struct bpf_insn *insn)
>   if (err)
>   return err;
>  
> - if (insn->src_reg == 0)
> - /* generic move 64-bit immediate into a register */
> + if (insn->src_reg == 0) {
> + /* generic move 64-bit immediate into a register,
> +  * only analyzer needs to collect the ld_imm value.
> +  */
> + u64 imm = ((u64)(insn + 1)->imm << 32) | (u32)insn->imm;
> +
> + if (!env->analyzer_ops)
> + return 0;

the check makes sense. thanks.
Acked-by: Alexei Starovoitov 

[PATCHv4 net-next 07/15] bpf: recognize 64bit immediate loads as consts

[Jakub Kicinski]

When running as parser interpret BPF_LD | BPF_IMM | BPF_DW
instructions as loading CONST_IMM with the value stored
in imm.  The verifier will continue not recognizing those
due to concerns about search space/program complexity
increase.

Signed-off-by: Jakub Kicinski 
---
v3:
 - limit to parsers.
---
 kernel/bpf/verifier.c | 14 --
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d93e78331b90..f5bed7cce08d 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1766,9 +1766,19 @@ static int check_ld_imm(struct bpf_verifier_env *env, 
struct bpf_insn *insn)
if (err)
return err;
 
-   if (insn->src_reg == 0)
-   /* generic move 64-bit immediate into a register */
+   if (insn->src_reg == 0) {
+   /* generic move 64-bit immediate into a register,
+* only analyzer needs to collect the ld_imm value.
+*/
+   u64 imm = ((u64)(insn + 1)->imm << 32) | (u32)insn->imm;
+
+   if (!env->analyzer_ops)
+   return 0;
+
+   regs[insn->dst_reg].type = CONST_IMM;
+   regs[insn->dst_reg].imm = imm;
return 0;
+   }
 
/* replace_map_fd_with_map_ptr() should have caught bad ld_imm64 */
BUG_ON(insn->src_reg != BPF_PSEUDO_MAP_FD);
-- 
1.9.1