From: Carlos O'Donell <carlos@redhat.com>
To: "H.J. Lu" <hjl.tools@gmail.com>, libc-alpha@sourceware.org
Subject: Re: [PATCH v2] x86-64: Check if mprotect works before rewriting PLT
Date: Mon, 15 Jan 2024 09:51:34 -0500 [thread overview]
Message-ID: <74cc87d8-0a54-d41d-078b-1aee336fb86c@redhat.com> (raw)
In-Reply-To: <20240112181941.3536012-1-hjl.tools@gmail.com>
On 1/12/24 13:19, H.J. Lu wrote:
> Systemd execution environment configuration may prohibit changing a memory
> mapping to become executable:
>
> MemoryDenyWriteExecute=
> Takes a boolean argument. If set, attempts to create memory mappings
> that are writable and executable at the same time, or to change existing
> memory mappings to become executable, or mapping shared memory segments
> as executable, are prohibited.
>
> When it is set, systemd service stops working if PLT rewrite is enabled.
> Check if mprotect works before rewriting PLT. This fixes BZ #31230.
> This also works with SELinux when deny_execmem is on.
LGTM. Good commit message and comments. Thank you!
Please commit this for 2.39.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
> ---
> .../unix/sysv/linux/x86_64/dl-plt-rewrite.h | 43 +++++++++++++++++++
> sysdeps/x86/cpu-features.c | 8 +++-
> sysdeps/x86_64/dl-plt-rewrite.h | 25 +++++++++++
> 3 files changed, 75 insertions(+), 1 deletion(-)
> create mode 100644 sysdeps/unix/sysv/linux/x86_64/dl-plt-rewrite.h
> create mode 100644 sysdeps/x86_64/dl-plt-rewrite.h
>
> diff --git a/sysdeps/unix/sysv/linux/x86_64/dl-plt-rewrite.h b/sysdeps/unix/sysv/linux/x86_64/dl-plt-rewrite.h
> new file mode 100644
> index 0000000000..ad637df930
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86_64/dl-plt-rewrite.h
> @@ -0,0 +1,43 @@
> +/* PLT rewrite helper function. Linux/x86-64 version.
> + Copyright (C) 2024 Free Software Foundation, Inc.
> +
> + 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/>. */
> +
> +#include <stdbool.h>
> +#include <sys/mman.h>
> +
> +static __always_inline bool
> +dl_plt_rewrite_supported (void)
> +{
> + /* PLT rewrite is enabled. Check if mprotect works. */
> + void *plt = (void *) INTERNAL_SYSCALL_CALL (mmap, NULL, 4096,
> + PROT_READ | PROT_WRITE,
> + MAP_PRIVATE | MAP_ANONYMOUS,
> + -1, 0);
> + if (__glibc_unlikely (plt == MAP_FAILED))
> + return false;
> +
> + /* Touch the PROT_READ | PROT_WRITE page. */
> + *(int32_t *) plt = 1;
> +
> + /* If the updated PROT_READ | PROT_WRITE page can be changed to
> + PROT_EXEC | PROT_READ, rewrite PLT. */
> + bool status = (INTERNAL_SYSCALL_CALL (mprotect, plt, 4096,
> + PROT_EXEC | PROT_READ) == 0);
> +
> + INTERNAL_SYSCALL_CALL (munmap, plt, 4096);
> +
> + return status;
> +}
> diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
> index 46bdaffbc2..25e6622a79 100644
> --- a/sysdeps/x86/cpu-features.c
> +++ b/sysdeps/x86/cpu-features.c
> @@ -28,10 +28,16 @@ extern void TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *)
> attribute_hidden;
>
> #if defined SHARED && defined __x86_64__
> +# include <dl-plt-rewrite.h>
> +
> static void
> TUNABLE_CALLBACK (set_plt_rewrite) (tunable_val_t *valp)
> {
> - if (valp->numval != 0)
> + /* We must be careful about where we put the call to
> + dl_plt_rewrite_supported() since it may generate
> + spurious SELinux log entries. It should only be
> + attempted if the user requested a PLT rewrite. */
OK.
> + if (valp->numval != 0 && dl_plt_rewrite_supported ())
> {
> /* Use JMPABS only on APX processors. */
> const struct cpu_features *cpu_features = __get_cpu_features ();
> diff --git a/sysdeps/x86_64/dl-plt-rewrite.h b/sysdeps/x86_64/dl-plt-rewrite.h
> new file mode 100644
> index 0000000000..cab6fe75ea
> --- /dev/null
> +++ b/sysdeps/x86_64/dl-plt-rewrite.h
> @@ -0,0 +1,25 @@
> +/* PLT rewrite helper function. x86-64 version.
> + Copyright (C) 2024 Free Software Foundation, Inc.
> +
> + 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/>. */
> +
> +#include <stdbool.h>
> +#include <sys/mman.h>
> +
> +static __always_inline bool
> +dl_plt_rewrite_supported (void)
> +{
> + return true;
> +}
--
Cheers,
Carlos.
next prev parent reply other threads:[~2024-01-15 14:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-12 18:19 H.J. Lu
2024-01-15 14:51 ` Carlos O'Donell [this message]
2024-01-16 17:36 ` Adhemerval Zanella Netto
2024-01-16 18:13 ` H.J. Lu
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