Merge tag 'clone3-tls-v5.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

Pull thread fixes from Christian Brauner:
 "This contains a series of patches to fix CLONE_SETTLS when used with
  clone3().

  The clone3() syscall passes the tls argument through struct clone_args
  instead of a register. This means, all architectures that do not
  implement copy_thread_tls() but still support CLONE_SETTLS via
  copy_thread() expecting the tls to be located in a register argument
  based on clone() are currently unfortunately broken. Their tls value
  will be garbage.

  The patch series fixes this on all architectures that currently define
  __ARCH_WANT_SYS_CLONE3. It also adds a compile-time check to ensure
  that any architecture that enables clone3() in the future is forced to
  also implement copy_thread_tls().

  My ultimate goal is to get rid of the copy_thread()/copy_thread_tls()
  split and just have copy_thread_tls() at some point in the not too
  distant future (Maybe even renaming copy_thread_tls() back to simply
  copy_thread() once the old function is ripped from all arches). This
  is dependent now on all arches supporting clone3().

  While all relevant arches do that now there are still four missing:
  ia64, m68k, sh and sparc. They have the system call reserved, but not
  implemented. Once they all implement clone3() we can get rid of
  ARCH_WANT_SYS_CLONE3 and HAVE_COPY_THREAD_TLS.

  This series also includes a minor fix for the arm64 uapi headers which
  caused __NR_clone3 to be missing from the exported user headers.

  Unfortunately the series came in a little late especially given that
  it touches a range of architectures. Due to the holidays not all arch
  maintainers responded in time probably due to their backlog. Will and
  Arnd have thankfully acked the arm specific changes.

  Given that the changes are straightforward and rather minimal combined
  with the fact the that clone3() with CLONE_SETTLS is broken I decided
  to send them post rc3 nonetheless"

* tag 'clone3-tls-v5.5-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
  um: Implement copy_thread_tls
  clone3: ensure copy_thread_tls is implemented
  xtensa: Implement copy_thread_tls
  riscv: Implement copy_thread_tls
  parisc: Implement copy_thread_tls
  arm: Implement copy_thread_tls
  arm64: Implement copy_thread_tls
  arm64: Move __ARCH_WANT_SYS_CLONE3 definition to uapi headers

1 files changed, 10 insertions, 0 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 2508a4f238a3..080809560072 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2578,6 +2578,16 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
 #endif
 
 #ifdef __ARCH_WANT_SYS_CLONE3
+
+/*
+ * copy_thread implementations handle CLONE_SETTLS by reading the TLS value from
+ * the registers containing the syscall arguments for clone. This doesn't work
+ * with clone3 since the TLS value is passed in clone_args instead.
+ */
+#ifndef CONFIG_HAVE_COPY_THREAD_TLS
+#error clone3 requires copy_thread_tls support in arch
+#endif
+
 noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 					      struct clone_args __user *uargs,
 					      size_t usize)