[PATCH v5 12/23] aarch64: Enable GCS in static linked exe

[Carlos O'Donell]

On 12/6/24 8:29 AM, Yury Khrustalev wrote:
> From: Szabolcs Nagy <szabolcs.nagy@arm.com>
> 
> Use the ARCH_SETUP_TLS hook to enable GCS in the static linked case.
> The system call must be inlined and then GCS is enabled on a top
> level stack frame that does not return and has no exception handlers
> above it.

Won't fail on old kernels because we don't check the prctl status.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  sysdeps/unix/sysv/linux/aarch64/libc-start.h | 44 ++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 sysdeps/unix/sysv/linux/aarch64/libc-start.h
> 
> diff --git a/sysdeps/unix/sysv/linux/aarch64/libc-start.h b/sysdeps/unix/sysv/linux/aarch64/libc-start.h
> new file mode 100644
> index 0000000000..ea6580fca6
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/aarch64/libc-start.h
> @@ -0,0 +1,44 @@
> +/* AArch64 definitions for libc main startup.
> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#ifndef _LIBC_START_H
> +#define _LIBC_START_H
> +
> +#ifndef SHARED
> +
> +# ifndef PR_SET_SHADOW_STACK_STATUS
> +#  define PR_SET_SHADOW_STACK_STATUS	75
> +# endif
> +
> +/* Must be on a top-level stack frame that does not return.  */
> +static inline void __attribute__((always_inline))
> +aarch64_libc_setup_tls (void)
> +{
> +  __libc_setup_tls ();
> +
> +  uint64_t s = GL(dl_aarch64_gcs);
> +  if (s != 0)
> +    INLINE_SYSCALL_CALL (prctl, PR_SET_SHADOW_STACK_STATUS, s, 0, 0, 0);
> +}
> +
> +# define ARCH_SETUP_IREL() apply_irel ()
> +# define ARCH_SETUP_TLS() aarch64_libc_setup_tls ()
> +# define ARCH_APPLY_IREL()
> +#endif /* ! SHARED  */
> +
> +#endif /* _LIBC_START_H  */