x86/CET: Fix property note parser [BZ #23467]

GNU_PROPERTY_X86_FEATURE_1_AND may not be the first property item.  We
need to check each property item until we reach the end of the property
or find GNU_PROPERTY_X86_FEATURE_1_AND.

This patch adds 2 tests.  The first test checks if IBT is enabled and
the second test reads the output from the first test to check if IBT
is is enabled.  The second second test fails if IBT isn't enabled
properly.

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

	[BZ #23467]
	* sysdeps/unix/sysv/linux/x86/Makefile (tests): Add
	tst-cet-property-1 and tst-cet-property-2 if CET is enabled.
	(CFLAGS-tst-cet-property-1.o): New.
	(ASFLAGS-tst-cet-property-dep-2.o): Likewise.
	($(objpfx)tst-cet-property-2): Likewise.
	($(objpfx)tst-cet-property-2.out): Likewise.
	* sysdeps/unix/sysv/linux/x86/tst-cet-property-1.c: New file.
	* sysdeps/unix/sysv/linux/x86/tst-cet-property-2.c: Likewise.
	* sysdeps/unix/sysv/linux/x86/tst-cet-property-dep-2.S: Likewise.
	* sysdeps/x86/dl-prop.h (_dl_process_cet_property_note): Parse
	each property item until GNU_PROPERTY_X86_FEATURE_1_AND is found.

5 files changed, 205 insertions, 9 deletions

diff --git a/sysdeps/unix/sysv/linux/x86/Makefile b/sysdeps/unix/sysv/linux/x86/Makefile
index a30fdb1dc1..7dc4e61756 100644
--- a/sysdeps/unix/sysv/linux/x86/Makefile
+++ b/sysdeps/unix/sysv/linux/x86/Makefile
@@ -25,6 +25,21 @@ tests += tst-saved_mask-1
 endif
 
 ifeq ($(enable-cet),yes)
+ifeq ($(subdir),elf)
+tests += tst-cet-property-1 tst-cet-property-2
+
+CFLAGS-tst-cet-property-1.o += -fcf-protection
+ASFLAGS-tst-cet-property-dep-2.o += -fcf-protection
+
+$(objpfx)tst-cet-property-2: $(objpfx)tst-cet-property-dep-2.o
+$(objpfx)tst-cet-property-2.out: $(objpfx)tst-cet-property-2 \
+				 $(objpfx)tst-cet-property-1.out
+	env $(run-program-env) $(test-via-rtld-prefix) \
+	  $(objpfx)tst-cet-property-2 \
+	  < $(objpfx)tst-cet-property-1.out > $@; \
+	  $(evaluate-test)
+endif
+
 ifeq ($(subdir),stdlib)
 tests += tst-cet-setcontext-1
 CFLAGS-tst-cet-setcontext-1.c += -mshstk
diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-property-1.c b/sysdeps/unix/sysv/linux/x86/tst-cet-property-1.c
new file mode 100644
index 0000000000..21130faefc
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/tst-cet-property-1.c
@@ -0,0 +1,44 @@
+/* Test CET property note parser.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+#include <elf.h>
+#include <tcb-offsets.h>
+
+/* This test prints out "IBT" if Intel indirect branch tracking (IBT)
+   is enabled at run-time, which is checked by tst-cet-property-2 to
+   verify that the IBT violation is caught on IBT machines.  */
+
+static int
+do_test (void)
+{
+  unsigned int feature_1;
+#ifdef __x86_64__
+# define SEG_REG "fs"
+#else
+# define SEG_REG "gs"
+#endif
+  asm ("movl %%" SEG_REG ":%P1, %0"
+       : "=r" (feature_1) : "i" (FEATURE_1_OFFSET));
+  if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT) != 0)
+    printf ("IBT\n");
+
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-property-2.c b/sysdeps/unix/sysv/linux/x86/tst-cet-property-2.c
new file mode 100644
index 0000000000..0531074ceb
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/tst-cet-property-2.c
@@ -0,0 +1,63 @@
+/* Test CET property note parser for [BZ #23467].
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <signal.h>
+#include <support/check.h>
+
+extern void bar (void);
+
+void
+__attribute__ ((noclone, noinline))
+test (void (*func_p) (void))
+{
+  func_p ();
+}
+
+/* bar contains an IBT violation if it is called indirectly via a
+   function pointer.  On IBT machines, it should lead to segfault
+   unless IBT is disabled by error.  */
+
+static void
+sig_handler (int signo)
+{
+  exit (EXIT_SUCCESS);
+}
+
+static int
+do_test (void)
+{
+  char buf[20];
+
+  if (scanf ("%20s", buf) != 1)
+    FAIL_UNSUPPORTED ("IBT not supported");
+
+  if (strcmp (buf, "IBT") != 0)
+    FAIL_UNSUPPORTED ("IBT not supported");
+
+  TEST_VERIFY_EXIT (signal (SIGSEGV, &sig_handler) != SIG_ERR);
+
+  /* Call bar via a function pointer to force an IBT violation.  */
+  test (bar);
+
+  return EXIT_FAILURE;
+}
+
+#include <support/test-driver.c>
diff --git a/sysdeps/unix/sysv/linux/x86/tst-cet-property-dep-2.S b/sysdeps/unix/sysv/linux/x86/tst-cet-property-dep-2.S
new file mode 100644
index 0000000000..5f5cad34d9
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86/tst-cet-property-dep-2.S
@@ -0,0 +1,63 @@
+/* Test CET property note parser.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <cet.h>
+
+	.text
+	.p2align 4,,15
+	.globl	bar
+	.type	bar, @function
+/* Since this function doesn't start with ENDBR, it should lead to the
+   IBT violation when called indirectly.  */
+bar:
+	.cfi_startproc
+	ret
+	.cfi_endproc
+	.size	bar, .-bar
+
+#if __SIZEOF_PTRDIFF_T__  == 8
+# define ALIGN 3
+#elif __SIZEOF_PTRDIFF_T__  == 4
+# define ALIGN 2
+#endif
+
+/* In NT_GNU_PROPERTY_TYPE_0 note, add a GNU_PROPERTY_STACK_SIZE property
+   before the GNU_PROPERTY_X86_FEATURE_1_AND property.  */
+	.section ".note.gnu.property", "a"
+	.p2align ALIGN
+	.long 1f - 0f		/* name length */
+	.long 5f - 2f		/* data length */
+	.long 5			/* note type */
+0:	.asciz "GNU"		/* vendor name */
+1:
+	.p2align ALIGN
+2:
+	.long 1			/* pr_type.  */
+	.long 4f - 3f		/* pr_datasz.  */
+3:
+#if __SIZEOF_PTRDIFF_T__  == 8
+	.long 0x800
+	.long 0x800
+#else
+	.long 0x08000800
+#endif
+4:
+	.p2align ALIGN
+5:
+
+	.section	.note.GNU-stack,"",@progbits
diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h
index 35d3f16a23..26c3131ac5 100644
--- a/sysdeps/x86/dl-prop.h
+++ b/sysdeps/x86/dl-prop.h
@@ -73,7 +73,7 @@ _dl_process_cet_property_note (struct link_map *l,
 	  unsigned char *ptr = (unsigned char *) (note + 1) + 4;
 	  unsigned char *ptr_end = ptr + note->n_descsz;
 
-	  while (ptr < ptr_end)
+	  do
 	    {
 	      unsigned int type = *(unsigned int *) ptr;
 	      unsigned int datasz = *(unsigned int *) (ptr + 4);
@@ -82,17 +82,28 @@ _dl_process_cet_property_note (struct link_map *l,
 	      if ((ptr + datasz) > ptr_end)
 		break;
 
-	      if (type == GNU_PROPERTY_X86_FEATURE_1_AND
-		  && datasz == 4)
+	      if (type == GNU_PROPERTY_X86_FEATURE_1_AND)
 		{
-		  unsigned int feature_1 = *(unsigned int *) ptr;
-		  if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT))
-		    l->l_cet |= lc_ibt;
-		  if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK))
-		    l->l_cet |= lc_shstk;
-		  break;
+		  /* The size of GNU_PROPERTY_X86_FEATURE_1_AND is 4
+		     bytes.  When seeing GNU_PROPERTY_X86_FEATURE_1_AND,
+		     we stop the search regardless if its size is correct
+		     or not.  There is no point to continue if this note
+		     is ill-formed.  */
+		  if (datasz == 4)
+		    {
+		      unsigned int feature_1 = *(unsigned int *) ptr;
+		      if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_IBT))
+			l->l_cet |= lc_ibt;
+		      if ((feature_1 & GNU_PROPERTY_X86_FEATURE_1_SHSTK))
+			l->l_cet |= lc_shstk;
+		    }
+		  return;
 		}
+
+	      /* Check the next property item.  */
+	      ptr += ALIGN_UP (datasz, sizeof (ElfW(Addr)));
 	    }
+	  while ((ptr_end - ptr) >= 8);
 	}
 
       /* NB: Note sections like .note.ABI-tag and .note.gnu.build-id are