Re: [PATCH bpf-next v5 3/6] bpf: Remove is_valid_bpf_tramp_flags()

On Wed, May 18, 2022 at 09:16:35AM -0400, Xu Kuohai wrote:

BPF_TRAM_F_XXX flags are not used by user code and are almost constant at compile time, so run time validation is a bit overkill. Remove is_valid_bpf_tramp_flags() and add some usage comments.

Signed-off-by: Xu Kuohai xukuohai@huawei.com Acked-by: Song Liu songliubraving@fb.com

Am I right in thinking this is independent of the arm64-specific bits, and could be taken on its own now?

Mark.

---

arch/x86/net/bpf_jit_comp.c | 20 -------------------- kernel/bpf/bpf_struct_ops.c | 3 +++ kernel/bpf/trampoline.c | 3 +++ 3 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index a2b6d197c226..7698ef3b4821 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1922,23 +1922,6 @@ static int invoke_bpf_mod_ret(const struct btf_func_model *m, u8 **pprog, return 0; } -static bool is_valid_bpf_tramp_flags(unsigned int flags) -{

• if ((flags & BPF_TRAMP_F_RESTORE_REGS) &&

•    (flags & BPF_TRAMP_F_SKIP_FRAME))
  

• return false;
  

• /*

• * BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,
  

• * and it must be used alone.
  

• */
  

• if ((flags & BPF_TRAMP_F_RET_FENTRY_RET) &&

•    (flags & ~BPF_TRAMP_F_RET_FENTRY_RET))
  

• return false;
  

• return true;

-}

/* Example:

• __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev);
• its 'struct btf_func_model' will be nr_args=2

@@ -2017,9 +2000,6 @@ int arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *image, void *i if (nr_args > 6) return -ENOTSUPP;

• if (!is_valid_bpf_tramp_flags(flags))

• return -EINVAL;
  

• /* Generated trampoline stack layout:
  • RBP + 8 [ return address ]

diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c index d9a3c9207240..0572cc5aeb28 100644 --- a/kernel/bpf/bpf_struct_ops.c +++ b/kernel/bpf/bpf_struct_ops.c @@ -341,6 +341,9 @@ int bpf_struct_ops_prepare_trampoline(struct bpf_tramp_links *tlinks, tlinks[BPF_TRAMP_FENTRY].links[0] = link; tlinks[BPF_TRAMP_FENTRY].nr_links = 1;

• /* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops,

• * and it must be used alone.
  

• */
  

  flags = model->ret_size > 0 ? BPF_TRAMP_F_RET_FENTRY_RET : 0; return arch_prepare_bpf_trampoline(NULL, image, image_end, model, flags, tlinks, NULL);

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c index 93c7675f0c9e..bd3f2e673874 100644 --- a/kernel/bpf/trampoline.c +++ b/kernel/bpf/trampoline.c @@ -358,6 +358,9 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr) if (tlinks[BPF_TRAMP_FEXIT].nr_links || tlinks[BPF_TRAMP_MODIFY_RETURN].nr_links)

• /* NOTE: BPF_TRAMP_F_RESTORE_REGS and BPF_TRAMP_F_SKIP_FRAME
  

•  * should not be set together.
  

•  */
  

  flags = BPF_TRAMP_F_CALL_ORIG | BPF_TRAMP_F_SKIP_FRAME;

if (ip_arg) -- 2.30.2