Implement process_vm_readv and process_vm_writev

[doanbaotrung]

Add same-process support for SYS_process_vm_readv and SYS_process_vm_writev. Import and validate guest iovec arrays, copy through guest memory in bounded chunks, and return short counts when a later buffer faults after partial progress.

Wire the syscall numbers through abi.h, dispatch.tbl, and syscall.c. Add test-process-vm coverage for scatter/gather reads and writes, short-copy fault behavior, bad flags, foreign PIDs, bad iovec pointers, oversized iovcnt, and zero-count calls. Include the test in the matrix.

Fix #197

---

Summary by cubic

Adds same-process support for SYS_process_vm_readv and SYS_process_vm_writev. Validates guest iovecs, copies through guest memory in safe chunks, and returns short counts on faults. Fixes #197.

• New Features
  • Wired syscall numbers and dispatch via abi.h, dispatch.tbl, and syscall.c.
  • Implemented iovec import/validation and bounded scatter/gather copying in io.c.
  • Error handling: -EINVAL for bad flags/oversized iovcnt, -ESRCH for foreign PIDs, -EFAULT for bad pointers; zero-count returns 0.
  • Added test-process-vm to the matrix covering scatter/gather reads/writes, short-copy behavior, and bad-input cases.

^{Written for commit 4fe2d64. Summary will update on new commits.}

[cubic-dev-ai]

2 issues found across 7 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="src/syscall/io.c">

<violation number="1" location="src/syscall/io.c:1844">
P2: PID values with nonzero upper register bits incorrectly return ESRCH instead of addressing the low-32-bit `pid_t`. Narrow `pid` before validation, matching the syscall ABI and other PID handlers.</violation>

<violation number="2" location="src/syscall/io.c:1844">
P2: The PID gate is stricter than the rest of the runtime’s process identity handling and rejects same-process aliases outright. That can turn a same-process memory copy into `ESRCH` even though the new feature is intended to work within the current guest process.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P2: PID values with nonzero upper register bits incorrectly return ESRCH instead of addressing the low-32-bit pid_t. Narrow pid before validation, matching the syscall ABI and other PID handlers.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At src/syscall/io.c, line 1844:

<comment>PID values with nonzero upper register bits incorrectly return ESRCH instead of addressing the low-32-bit `pid_t`. Narrow `pid` before validation, matching the syscall ABI and other PID handlers.</comment>

<file context>
@@ -1730,6 +1730,165 @@ int64_t sys_pwritev2(guest_t *g,
+{
+    if (flags != 0)
+        return -LINUX_EINVAL;
+    if (pid <= 0 || pid != proc_get_pid())
+        return -LINUX_ESRCH;
+    if (local_iovcnt == 0 || remote_iovcnt == 0)
</file context>

Suggested change

	if (pid <= 0 || pid != proc_get_pid())
	if ((int) pid <= 0 || (int) pid != proc_get_pid())

[cubic-dev-ai]

P2: The PID gate is stricter than the rest of the runtime’s process identity handling and rejects same-process aliases outright. That can turn a same-process memory copy into ESRCH even though the new feature is intended to work within the current guest process.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At src/syscall/io.c, line 1844:

<comment>The PID gate is stricter than the rest of the runtime’s process identity handling and rejects same-process aliases outright. That can turn a same-process memory copy into `ESRCH` even though the new feature is intended to work within the current guest process.</comment>

<file context>
@@ -1730,6 +1730,165 @@ int64_t sys_pwritev2(guest_t *g,
+{
+    if (flags != 0)
+        return -LINUX_EINVAL;
+    if (pid <= 0 || pid != proc_get_pid())
+        return -LINUX_ESRCH;
+    if (local_iovcnt == 0 || remote_iovcnt == 0)
</file context>