Add an internal wrapper for clone, clone2 and clone3

System Internals / glibc - H.J. Lu [] - 14 July 2021 13:33 UTC

The clone3 system call (since Linux 5.3) provides a superset of the functionality of clone and clone2. It also provides a number of API improvements, including the ability to specify the size of the child's stack area which can be used by kernel to compute the shadow stack size when allocating the shadow stack. Add:

extern int __clone_internal (struct clone_args *__cl_args, int (*__func) (void *__arg), void *__arg);

to provide an abstract interface for clone, clone2 and clone3.

1. Simplify stack management for thread creation by passing both stack base and size to create_thread. 2. Consolidate clone vs clone2 differences into a single file. 3. Call __clone3 if HAVE_CLONE3_WAPPER is defined. If __clone3 returns
-1 with ENOSYS, fall back to clone or clone2. 4. Use only __clone_internal to clone a thread. Since the stack size argument for create_thread is now unconditional, always pass stack size to create_thread. 5. Enable the public clone3 wrapper in the future after it has been added to all targets.

NB: Sandbox will return ENOSYS on clone3 in both Chromium:

The following revision refers to this bug:

commit 218438259dd795456f0a48f67cbe5b4e520db88b Author: Matthew Denton Date: Thu Jun 03 20:06:13 2021

Linux sandbox: return ENOSYS for clone3

Because clone3 uses a pointer argument rather than a flags argument, we cannot examine the contents with seccomp, which is essential to preventing sandboxed processes from starting other processes. So, we won't be able to support clone3 in Chromium. This CL modifies the BPF policy to return ENOSYS for clone3 so glibc always uses the fallback to clone.

Bug: 1213452 Change-Id: I7c7c585a319e0264eac5b1ebee1a45be2d782303 Reviewed-on:

d8ea0d0168 Add an internal wrapper for clone, clone2 and clone3
include/clone_internal.h | 16 ++++++
nptl/allocatestack.c | 59 ++-------------------
nptl/pthread_create.c | 38 +++++++------
sysdeps/unix/sysv/linux/Makefile | 3 +-
sysdeps/unix/sysv/linux/clone-internal.c | 91 ++++++++++++++++++++++++++++++++
sysdeps/unix/sysv/linux/clone3.c | 1 +
sysdeps/unix/sysv/linux/clone3.h | 67 +++++++++++++++++++++++
sysdeps/unix/sysv/linux/spawni.c | 26 ++++-----
8 files changed, 213 insertions(+), 88 deletions(-)


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