bpf: Remove is_valid_bpf_tramp_flags()

Before generating bpf trampoline, x86 calls is_valid_bpf_tramp_flags()
to check the input flags. This check is architecture independent.
So, to be consistent with x86, arm64 should also do this check
before generating bpf trampoline.

However, the BPF_TRAMP_F_XXX flags are not used by user code and the
flags argument is almost constant at compile time, so this run time
check is a bit redundant.

Remove is_valid_bpf_tramp_flags() and add some comments to the usage of
BPF_TRAMP_F_XXX flags, as suggested by Alexei.

Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220711150823.2128542-2-xukuohai@huawei.com

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index b88f43c..d2614f1 100644 (file)
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -1936,23 +1936,6 @@ 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
@@ -2031,9 +2014,6 @@ 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 7e0068c..84b2d9d 100644 (file)
--- 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 6cd2265..fd69812 100644 (file)
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -360,6 +360,9 @@ 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)