On Fri, 26 Feb 2021 at 16:32, Mathieu Desnoyers
[off-list ref] wrote:

----- On Feb 26, 2021, at 8:51 AM, Piotr Figiel figiel@google.com wrote:
[...]

quoted

---
v2:
Applied review comments:
- changed return value from the ptrace request to the size of the
  configuration structure
- expanded configuration structure with the flags field and
  the rseq abi structure size

[...]

quoted

+#define PTRACE_GET_RSEQ_CONFIGURATION        0x420f
+
+struct ptrace_rseq_configuration {
+     __u64 rseq_abi_pointer;
+     __u32 rseq_abi_size;
+     __u32 signature;
+     __u32 flags;
+     __u32 pad;
+};
+

[...]

quoted

+#ifdef CONFIG_RSEQ
+static long ptrace_get_rseq_configuration(struct task_struct *task,
+                                       unsigned long size, void __user *data)
+{
+     struct ptrace_rseq_configuration conf = {
+             .rseq_abi_pointer = (u64)(uintptr_t)task->rseq,
+             .rseq_abi_size = sizeof(*task->rseq),
+             .signature = task->rseq_sig,
+             .flags = 0,
+     };
+
+     size = min_t(unsigned long, size, sizeof(conf));
+     if (copy_to_user(data, &conf, size))
+             return -EFAULT;
+     return sizeof(conf);
+}

I think what Florian was after would be:

struct ptrace_rseq_configuration {
        __u32 size;  /* size of struct ptrace_rseq_configuration */
        __u32 flags;
        __u64 rseq_abi_pointer;
        __u32 signature;
        __u32 pad;
};

where:

    .size = sizeof(struct ptrace_rseq_configuration),

This way, the configuration structure can be expanded in the future. The
rseq ABI structure is by definition fixed-size, so there is no point in
having its size here.

Florian, did I understand your request correctly, or am I missing your point ?

In this case returning sizeof(conf) would serve the same purpose, wouldn't it?

Best Regards
Michał Mirosław

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