[v5,5/7] Use hidden visibility for early static PIE code
Commit Message
Extern symbol access in position independent code usually involves GOT
indirection which needs RELATIVE reloc in a static linked PIE. (On
some targets this is avoided e.g. because the linker can relax a GOT
access to a pc-relative access, but this is not generally true.) Code
that runs before static PIE self relocation must avoid relying on
dynamic relocations which can be ensured by using hidden visibility.
However we cannot just make all symbols hidden:
On i386, all calls to IFUNC functions must go through PLT and calls to
hidden functions CANNOT go through PLT in PIE since EBX used in PIE PLT
may not be set up for local calls to hidden IFUNC functions.
This patch aims to make symbol references hidden in code that is used
before and by _dl_relocate_static_pie when building a static PIE libc.
Note: for an object that is used in the startup code, its references
and definition may not have consistent visibility: it is only forced
hidden in the startup code.
This is needed for fixing bug 27072.
Co-authored-by: H.J. Lu <hjl.tools@gmail.com>
---
csu/libc-start.c | 4 ++++
elf/dl-reloc-static-pie.c | 2 ++
elf/dl-support.c | 6 ++++++
elf/dl-tunables.c | 4 ++++
elf/enbl-secure.c | 4 ++++
misc/sbrk.c | 4 ++++
sysdeps/unix/sysv/linux/aarch64/libc-start.c | 5 +++++
sysdeps/x86/libc-start.c | 5 +++++
8 files changed, 34 insertions(+)
Comments
On 20/01/2021 12:31, Szabolcs Nagy via Libc-alpha wrote:
> Extern symbol access in position independent code usually involves GOT
> indirection which needs RELATIVE reloc in a static linked PIE. (On
> some targets this is avoided e.g. because the linker can relax a GOT
> access to a pc-relative access, but this is not generally true.) Code
> that runs before static PIE self relocation must avoid relying on
> dynamic relocations which can be ensured by using hidden visibility.
> However we cannot just make all symbols hidden:
>
> On i386, all calls to IFUNC functions must go through PLT and calls to
> hidden functions CANNOT go through PLT in PIE since EBX used in PIE PLT
> may not be set up for local calls to hidden IFUNC functions.
>
> This patch aims to make symbol references hidden in code that is used
> before and by _dl_relocate_static_pie when building a static PIE libc.
> Note: for an object that is used in the startup code, its references
> and definition may not have consistent visibility: it is only forced
> hidden in the startup code.
>
> This is needed for fixing bug 27072.
>
> Co-authored-by: H.J. Lu <hjl.tools@gmail.com>
LGTM, thanks.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> ---
> csu/libc-start.c | 4 ++++
> elf/dl-reloc-static-pie.c | 2 ++
> elf/dl-support.c | 6 ++++++
> elf/dl-tunables.c | 4 ++++
> elf/enbl-secure.c | 4 ++++
> misc/sbrk.c | 4 ++++
> sysdeps/unix/sysv/linux/aarch64/libc-start.c | 5 +++++
> sysdeps/x86/libc-start.c | 5 +++++
> 8 files changed, 34 insertions(+)
>
> diff --git a/csu/libc-start.c b/csu/libc-start.c
> index 5b9ce1d158..a2f6e12728 100644
> --- a/csu/libc-start.c
> +++ b/csu/libc-start.c
> @@ -15,6 +15,10 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +#if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +#endif
> #include <assert.h>
> #include <stdlib.h>
> #include <stdio.h>
Ok.
> diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
> index a8d964061e..d5bd2f31e9 100644
> --- a/elf/dl-reloc-static-pie.c
> +++ b/elf/dl-reloc-static-pie.c
> @@ -17,6 +17,8 @@
> <https://www.gnu.org/licenses/>. */
>
> #if ENABLE_STATIC_PIE
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +# pragma GCC visibility push(hidden)
> #include <unistd.h>
> #include <ldsodefs.h>
> #include "dynamic-link.h"
Ok.
> diff --git a/elf/dl-support.c b/elf/dl-support.c
> index 2434c470c7..7abb65d8e3 100644
> --- a/elf/dl-support.c
> +++ b/elf/dl-support.c
> @@ -19,6 +19,12 @@
> /* This file defines some things that for the dynamic linker are defined in
> rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking. */
>
> +#include <string.h>
> +/* Mark symbols hidden in static PIE for early self relocation to work.
> + Note: string.h may have ifuncs which cannot be hidden on i686. */
> +#if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +#endif
> #include <errno.h>
> #include <libintl.h>
> #include <stdlib.h>
Ok.
> diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
> index e44476f204..b1a50b8469 100644
> --- a/elf/dl-tunables.c
> +++ b/elf/dl-tunables.c
> @@ -18,6 +18,10 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +#if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +#endif
> #include <startup.h>
> #include <stdint.h>
> #include <stdbool.h>
Ok.
> diff --git a/elf/enbl-secure.c b/elf/enbl-secure.c
> index 5dcf649626..9e47526bd3 100644
> --- a/elf/enbl-secure.c
> +++ b/elf/enbl-secure.c
> @@ -19,6 +19,10 @@
> /* This file is used in the static libc. For the shared library,
> dl-sysdep.c defines and initializes __libc_enable_secure. */
>
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +#if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +#endif
> #include <startup.h>
> #include <libc-internal.h>
>
Ok.
> diff --git a/misc/sbrk.c b/misc/sbrk.c
> index 99b3fb517e..95800b32aa 100644
> --- a/misc/sbrk.c
> +++ b/misc/sbrk.c
> @@ -15,6 +15,10 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +#if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +#endif
> #include <errno.h>
> #include <libc-internal.h>
> #include <stdbool.h>
Ok.
> diff --git a/sysdeps/unix/sysv/linux/aarch64/libc-start.c b/sysdeps/unix/sysv/linux/aarch64/libc-start.c
> index f816f04ee1..e1604a6ed0 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/libc-start.c
> +++ b/sysdeps/unix/sysv/linux/aarch64/libc-start.c
> @@ -17,6 +17,11 @@
> <https://www.gnu.org/licenses/>. */
>
> #ifndef SHARED
> +
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +# if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +# endif
> # include <ldsodefs.h>
> # include <cpu-features.c>
>
Ok.
> diff --git a/sysdeps/x86/libc-start.c b/sysdeps/x86/libc-start.c
> index 4bbd7d555b..d30aec2aa1 100644
> --- a/sysdeps/x86/libc-start.c
> +++ b/sysdeps/x86/libc-start.c
> @@ -16,6 +16,11 @@
> <https://www.gnu.org/licenses/>. */
>
> #ifndef SHARED
> +
> +/* Mark symbols hidden in static PIE for early self relocation to work. */
> +# if BUILD_PIE_DEFAULT
> +# pragma GCC visibility push(hidden)
> +# endif
> /* Define I386_USE_SYSENTER to support syscall during startup in static
> PIE. */
> # include <startup.h>
>
Ok.
@@ -15,6 +15,10 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
@@ -17,6 +17,8 @@
<https://www.gnu.org/licenses/>. */
#if ENABLE_STATIC_PIE
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+# pragma GCC visibility push(hidden)
#include <unistd.h>
#include <ldsodefs.h>
#include "dynamic-link.h"
@@ -19,6 +19,12 @@
/* This file defines some things that for the dynamic linker are defined in
rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking. */
+#include <string.h>
+/* Mark symbols hidden in static PIE for early self relocation to work.
+ Note: string.h may have ifuncs which cannot be hidden on i686. */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
#include <errno.h>
#include <libintl.h>
#include <stdlib.h>
@@ -18,6 +18,10 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
#include <startup.h>
#include <stdint.h>
#include <stdbool.h>
@@ -19,6 +19,10 @@
/* This file is used in the static libc. For the shared library,
dl-sysdep.c defines and initializes __libc_enable_secure. */
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
#include <startup.h>
#include <libc-internal.h>
@@ -15,6 +15,10 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
#include <errno.h>
#include <libc-internal.h>
#include <stdbool.h>
@@ -17,6 +17,11 @@
<https://www.gnu.org/licenses/>. */
#ifndef SHARED
+
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+# if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+# endif
# include <ldsodefs.h>
# include <cpu-features.c>
@@ -16,6 +16,11 @@
<https://www.gnu.org/licenses/>. */
#ifndef SHARED
+
+/* Mark symbols hidden in static PIE for early self relocation to work. */
+# if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+# endif
/* Define I386_USE_SYSENTER to support syscall during startup in static
PIE. */
# include <startup.h>