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[PATCH v2 2/3] [MIPS] Define DL_EXEC_STACK_OVERRIDE

From: Dragan Mladjenovic <dmladjenovic at wavecomp dot com>
To: "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>
Cc: Joseph Myers <joseph at codesourcery dot com>, Carlos O'Donell <carlos at redhat dot com>, "Maciej W. Rozycki" <macro at linux-mips dot org>, Faraz Shahbazker <fshahbazker at wavecomp dot com>, Dragan Mladjenovic <dmladjenovic at wavecomp dot com>
Date: Tue, 16 Jul 2019 11:16:02 +0000
Subject: [PATCH v2 2/3] [MIPS] Define DL_EXEC_STACK_OVERRIDE
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References: <1563214941-16203-1-git-send-email-dmladjenovic@wavecomp.com> <1563275697-30825-1-git-send-email-dmladjenovic@wavecomp.com>

For hard-float builds targeting minimum Linux kernel version lower than
4.8 DL_EXEC_STACK_OVERRIDE will request executable stack if it detects
that runtime kernel version is also lower than 4.8.

Build now detects if mips toolchain uses GNU.stack note and updates
the expected result of check-execstack accordingly.

	* sysdeps/unix/sysv/linux/mips/Makefile
	[$(subdir) == elf][$(mips-float) == hard]
	(tests): Add tst-execstack-ovrd and tst-execstack-ovrd1.
	(tests-static): Add tst-execstack-ovrd-static and
	tst-execstack-ovrd1-static.
	(LDFLAGS-tst-execstack-ovrd*, tst-execstack-ovrd*-ENV): New rules.
	* sysdeps/unix/sysv/linux/mips/Makefile
	[$(subdir) == elf][$(mips-has-gnustack) != yes]
	(test-xfail-check-execstack): Move test-xfail-check-execstack here.
	(test-xfail-tst-execstack-ovrd1): New xfail.
	* sysdeps/unix/sysv/linux/mips/configure.ac
	(mips-has-gnustack): New var. Set to value of libc_cv_as_noexecstack.
	(mips-float): New var. Set to value of libc_mips_float.
	* sysdeps/unix/sysv/linux/mips/configure: Regenerated.
	* sysdeps/unix/sysv/linux/mips/ldsodefs.h
	(__GNU_STACK_SAFE_KERNEL_VERSION): New. Define to 4.8.0.
	(DL_EXEC_STACK_OVERRIDE): New. Check dl_osversion against previous define.
	* sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd-static.c: New file.
	* sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c: New file.
	* sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1-static.c: New file.
	* sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c: New file.
---
 sysdeps/unix/sysv/linux/mips/Makefile              | 26 ++++++++++++++++++----
 sysdeps/unix/sysv/linux/mips/configure.ac          |  3 +++
 sysdeps/unix/sysv/linux/mips/ldsodefs.h            | 11 +++++++++
 .../sysv/linux/mips/tst-execstack-ovrd-static.c    |  1 +
 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c  |  2 ++
 .../sysv/linux/mips/tst-execstack-ovrd1-static.c   |  1 +
 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c | 10 +++++++++
 7 files changed, 50 insertions(+), 4 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd-static.c
 create mode 100644 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c
 create mode 100644 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1-static.c
 create mode 100644 sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c

diff --git a/sysdeps/unix/sysv/linux/mips/Makefile b/sysdeps/unix/sysv/linux/mips/Makefile
index 8217f42..328f0b4 100644
--- a/sysdeps/unix/sysv/linux/mips/Makefile
+++ b/sysdeps/unix/sysv/linux/mips/Makefile
@@ -64,11 +64,29 @@ sysdep-dl-routines += dl-static
 sysdep_routines += dl-vdso
 endif
 
-# Supporting non-executable stacks on MIPS requires changes to both
-# the Linux kernel and glibc.  See
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00567.html> and
-# <https://sourceware.org/ml/libc-alpha/2016-01/msg00719.html>.
+ifeq ($(mips-float),hard)
+tests-static += tst-execstack-ovrd-static
+tests += tst-execstack-ovrd-static
+tests += tst-execstack-ovrd
+tests-static += tst-execstack-ovrd1-static
+tests += tst-execstack-ovrd1-static
+tests += tst-execstack-ovrd1
+LDFLAGS-tst-execstack-ovrd = -Wl,-z,noexecstack
+LDFLAGS-tst-execstack-ovrd-static = -Wl,-z,noexecstack
+LDFLAGS-tst-execstack-ovrd1 = -Wl,-z,noexecstack
+LDFLAGS-tst-execstack-ovrd1-static = -Wl,-z,noexecstack
+tst-execstack-ovrd-ENV = LD_ASSUME_KERNEL=4.5.0
+tst-execstack-ovrd-static-ENV = LD_ASSUME_KERNEL=4.5.0
+tst-execstack-ovrd1-ENV = LD_ASSUME_KERNEL=4.8.0
+tst-execstack-ovrd1-static-ENV = LD_ASSUME_KERNEL=4.8.0
+endif
+# If the compiler doesn't use GNU.stack note,
+# thease tests are expected to fail.
+ifneq ($(mips-has-gnustack),yes)
 test-xfail-check-execstack = yes
+test-xfail-tst-execstack-ovrd1 = yes
+endif
+
 endif
 
 ifeq ($(subdir),stdlib)
diff --git a/sysdeps/unix/sysv/linux/mips/configure.ac b/sysdeps/unix/sysv/linux/mips/configure.ac
index 9147aa4..1ff77e7 100644
--- a/sysdeps/unix/sysv/linux/mips/configure.ac
+++ b/sysdeps/unix/sysv/linux/mips/configure.ac
@@ -118,6 +118,9 @@ fi
 LIBC_CONFIG_VAR([default-abi],
   [${libc_mips_abi}_${libc_mips_float}${libc_mips_nan}])
 
+LIBC_CONFIG_VAR([mips-has-gnustack],[${libc_cv_as_noexecstack}])
+LIBC_CONFIG_VAR([mips-float],[${libc_mips_float}])
+
 case $machine in
 mips/mips64/n64/*)
   LIBC_SLIBDIR_RTLDDIR([lib64], [lib64])
diff --git a/sysdeps/unix/sysv/linux/mips/ldsodefs.h b/sysdeps/unix/sysv/linux/mips/ldsodefs.h
index 8dde855..803fdd1 100644
--- a/sysdeps/unix/sysv/linux/mips/ldsodefs.h
+++ b/sysdeps/unix/sysv/linux/mips/ldsodefs.h
@@ -37,4 +37,15 @@ extern void _dl_static_init (struct link_map *map);
    || (osabi == ELFOSABI_SYSV && ver < 4)		\
    || (osabi == ELFOSABI_GNU && ver < LIBC_ABI_MAX))
 
+
+#define __GNU_STACK_SAFE_KERNEL_VERSION (0x040800)
+
+#ifdef __mips_hard_float
+# if (__LINUX_KERNEL_VERSION < __GNU_STACK_SAFE_KERNEL_VERSION)
+#  undef DL_EXEC_STACK_OVERRIDE
+#  define DL_EXEC_STACK_OVERRIDE        \
+                 ((GLRO(dl_osversion) < __GNU_STACK_SAFE_KERNEL_VERSION))
+# endif
+#endif
+
 #endif /* ldsodefs.h */
diff --git a/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd-static.c b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd-static.c
new file mode 100644
index 0000000..0e5e61b
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd-static.c
@@ -0,0 +1 @@
+#include "tst-execstack-ovrd.c"
diff --git a/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c
new file mode 100644
index 0000000..9d2f4ef
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd.c
@@ -0,0 +1,2 @@
+#include "tst-execstack-prog.c"
+
diff --git a/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1-static.c b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1-static.c
new file mode 100644
index 0000000..e45ac94
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1-static.c
@@ -0,0 +1 @@
+#include "tst-execstack-ovrd1.c"
diff --git a/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c
new file mode 100644
index 0000000..953dd37
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/mips/tst-execstack-ovrd1.c
@@ -0,0 +1,10 @@
+#include <signal.h>
+
+/* This test will fail (not produce a SIGSEGV) either because
+   DL_SYSDEP_OSCHECK detects that we are running on kernel older
+   than what we specify via LD_ASSUME_KERNEL or the execution
+   environment doesn't support NX semantics (no RIXI).  */
+#define EXPECTED_SIGNAL SIGSEGV
+
+#include "tst-execstack-prog.c"
+
-- 
1.9.1

References:
- [PATCH v2 0/3] Mips support for PT_GNU_STACK
  - From: Dragan Mladjenovic
- [PATCH v2 1/3] [ELF] Allow the machine support to enforce executable stack
  - From: Dragan Mladjenovic

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