On 5/17/2022 11:53 PM, Alexei Starovoitov wrote:

On Tue, May 17, 2022 at 03:18:35AM -0400, Xu Kuohai wrote:

quoted

 
+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;
+}
+
+int bpf_prepare_trampoline(struct bpf_tramp_image *tr, void *image,
+			   void *image_end, const struct btf_func_model *m,
+			   u32 flags, struct bpf_tramp_links *tlinks,
+			   void *orig_call)
+{
+	if (!is_valid_bpf_tramp_flags(flags))
+		return -EINVAL;
+
+	return arch_prepare_bpf_trampoline(tr, image, image_end, m, flags,
+					   tlinks, orig_call);
+}

It's an overkill to introduce a new helper function just to validate
flags that almost compile time constants.
The flags are not user supplied.
Please move /* BPF_TRAMP_F_RET_FENTRY_RET is only used by bpf_struct_ops ... */
comment to bpf_struct_ops.c right before it calls arch_prepare_bpf_trampoline()
And add a comment to trampoline.c saying that BPF_TRAMP_F_RESTORE_REGS
and BPF_TRAMP_F_SKIP_FRAME should not be set together.
We could add a warn_on there or in arch code, but feels like overkill.
.

OK, will fix in next version.



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