[PATCH v3] ARM: Add pointer encryption support.

classic Classic list List threaded Threaded
2 messages Options
Reply | Threaded
Open this post in threaded view
|

[PATCH v3] ARM: Add pointer encryption support.

Will Newton

Add support for pointer encryption in glibc internal structures in C
and assembler code. Pointer encryption is a glibc security feature
described here:

https://sourceware.org/glibc/wiki/PointerEncryption

The ARM implementation uses global variables instead of thread pointer
relative accesses to get the value of the pointer encryption guard
because accessing the thread pointer can be very expensive on older
ARM cores.

ports/ChangeLog.arm:

2013-09-27  Will Newton  <[hidden email]>

        * sysdeps/arm/__longjmp.S (__longjmp): Demangle fp, sp
        and lr when restoring register values.
        * sysdeps/arm/include/bits/setjmp.h (JMP_BUF_REGLIST): Remove
        sp and lr from list and replace fp with a4.
        * sysdeps/arm/jmpbuf-unwind.h (_jmpbuf_sp): New function.
        (_JMPBUF_UNWINDS_ADJ): Call _jmpbuf_sp.
        * sysdeps/arm/setjmp.S (__sigsetjmp): Mangle fp, sp and lr
        before storing register values.
        * sysdeps/arm/sysdep.h (LDST_GLOBAL): New macro.
        * sysdeps/unix/sysv/linux/arm/sysdep.h (PTR_MANGLE): New macro.
        (PTR_DEMANGLE): Likewise. (PTR_MANGLE2): Likewise.
        (PTR_DEMANGLE2): Likewise.
---
 ports/sysdeps/arm/__longjmp.S              | 14 ++++++++++
 ports/sysdeps/arm/include/bits/setjmp.h    |  5 ++--
 ports/sysdeps/arm/jmpbuf-unwind.h          | 13 +++++++++-
 ports/sysdeps/arm/setjmp.S                 | 14 ++++++++++
 ports/sysdeps/arm/sysdep.h                 | 12 +++++++++
 ports/sysdeps/unix/sysv/linux/arm/sysdep.h | 41 +++++++++++++++++++++++++++---
 6 files changed, 93 insertions(+), 6 deletions(-)

Changes in v3:
 - Added comments
 - Described internals on the wiki and added a link in commit message
 - Improved commit message
 - Replaced conditional !IS_IN_nscd with !NOT_IN_libc || IS_IN_libpthread

diff --git a/ports/sysdeps/arm/__longjmp.S b/ports/sysdeps/arm/__longjmp.S
index a5edede..2b1f7f4 100644
--- a/ports/sysdeps/arm/__longjmp.S
+++ b/ports/sysdeps/arm/__longjmp.S
@@ -34,10 +34,24 @@ ENTRY (__longjmp)
  sfi_breg ip, \
  ldr r4, [\B, #32] /* jmpbuf's sp */
  cfi_undefined (r4)
+#ifdef PTR_DEMANGLE
+ PTR_DEMANGLE (r4, r4, a3, a4)
+#endif
  CHECK_SP (r4)
 #endif
  sfi_sp sfi_breg ip, \
  ldmia \B!, JMP_BUF_REGLIST
+#ifdef PTR_DEMANGLE
+ PTR_DEMANGLE (fp, a4, a3, a2)
+ ldr a4, [ip], #4
+ PTR_DEMANGLE2 (sp, a4, a3)
+ ldr a4, [ip], #4
+ PTR_DEMANGLE2 (lr, a4, a3)
+#else
+ mov fp, a4
+ ldr sp, [ip], #4
+ ldr lr, [ip], #4
+#endif
  cfi_restore (v1)
  cfi_restore (v2)
  cfi_restore (v3)
diff --git a/ports/sysdeps/arm/include/bits/setjmp.h b/ports/sysdeps/arm/include/bits/setjmp.h
index 1559d7b..64505dc 100644
--- a/ports/sysdeps/arm/include/bits/setjmp.h
+++ b/ports/sysdeps/arm/include/bits/setjmp.h
@@ -26,8 +26,9 @@

 #ifndef _ISOMAC
 /* Register list for a ldm/stm instruction to load/store
-   the general registers from a __jmp_buf.  */
-# define JMP_BUF_REGLIST {v1-v6, sl, fp, sp, lr}
+   the general registers from a __jmp_buf. The a4 register
+   contains fp at this point.  */
+# define JMP_BUF_REGLIST {a4, v1-v6, sl}

 /* Index of __jmp_buf where the sp register resides.  */
 # define __JMP_BUF_SP 8
diff --git a/ports/sysdeps/arm/jmpbuf-unwind.h b/ports/sysdeps/arm/jmpbuf-unwind.h
index 0863540..1b0d020 100644
--- a/ports/sysdeps/arm/jmpbuf-unwind.h
+++ b/ports/sysdeps/arm/jmpbuf-unwind.h
@@ -17,6 +17,7 @@

 #include <setjmp.h>
 #include <stdint.h>
+#include <sysdep.h>
 #include <unwind.h>

 /* Test if longjmp to JMPBUF would unwind the frame
@@ -27,8 +28,18 @@
 #define _JMPBUF_CFA_UNWINDS_ADJ(_jmpbuf, _context, _adj) \
   _JMPBUF_UNWINDS_ADJ (_jmpbuf, (void *) _Unwind_GetCFA (_context), _adj)

+static inline uintptr_t __attribute__ ((unused))
+_jmpbuf_sp (__jmp_buf regs)
+{
+  uintptr_t sp = regs[__JMP_BUF_SP];
+#ifdef PTR_DEMANGLE
+  PTR_DEMANGLE (sp);
+#endif
+  return sp;
+}
+
 #define _JMPBUF_UNWINDS_ADJ(_jmpbuf, _address, _adj) \
-  ((uintptr_t) (_address) - (_adj) < (uintptr_t) (_jmpbuf)[__JMP_BUF_SP] - (_adj))
+  ((uintptr_t) (_address) - (_adj) < _jmpbuf_sp (_jmpbuf) - (_adj))

 /* We use the normal longjmp for unwinding.  */
 #define __libc_unwind_longjmp(buf, val) __libc_longjmp (buf, val)
diff --git a/ports/sysdeps/arm/setjmp.S b/ports/sysdeps/arm/setjmp.S
index a6c161d..b38b919 100644
--- a/ports/sysdeps/arm/setjmp.S
+++ b/ports/sysdeps/arm/setjmp.S
@@ -24,11 +24,25 @@
 #include <arm-features.h>

 ENTRY (__sigsetjmp)
+#ifdef PTR_MANGLE
+ PTR_MANGLE (a4, fp, a3, ip)
+#else
+ mov a4, fp
+#endif
  mov ip, r0

  /* Save registers */
  sfi_breg ip, \
  stmia \B!, JMP_BUF_REGLIST
+#ifdef PTR_MANGLE
+ PTR_MANGLE2 (a4, sp, a3)
+ str a4, [ip], #4
+ PTR_MANGLE2 (a4, lr, a3)
+ str a4, [ip], #4
+#else
+ str sp, [ip], #4
+ str lr, [ip], #4
+#endif

 #if !defined ARM_ASSUME_NO_IWMMXT || defined __SOFTFP__
 # define NEED_HWCAP 1
diff --git a/ports/sysdeps/arm/sysdep.h b/ports/sysdeps/arm/sysdep.h
index 5501597..3823617 100644
--- a/ports/sysdeps/arm/sysdep.h
+++ b/ports/sysdeps/arm/sysdep.h
@@ -171,6 +171,18 @@
 99: OP R, [pc, T]
 # endif

+/* Load or store to/from a global EXPR into/from R, using T.  */
+# define LDST_GLOBAL(OP, R, T, EXPR) \
+ ldr T, 99f; \
+ ldr R, 100f; \
+98: add T, T, pc; \
+ ldr T, [T, R]; \
+ .subsection 2; \
+99: .word _GLOBAL_OFFSET_TABLE_ - 98b - PC_OFS; \
+100: .word EXPR##(GOT); \
+ .previous; \
+ OP R, [T]
+
 /* Cope with negative memory offsets, which thumb can't encode.
    Use NEGOFF_ADJ_BASE to (conditionally) alter the base register,
    and then NEGOFF_OFF1 to use 0 for thumb and the offset for arm,
diff --git a/ports/sysdeps/unix/sysv/linux/arm/sysdep.h b/ports/sysdeps/unix/sysv/linux/arm/sysdep.h
index b195d8e..2bd187e 100644
--- a/ports/sysdeps/unix/sysv/linux/arm/sysdep.h
+++ b/ports/sysdeps/unix/sysv/linux/arm/sysdep.h
@@ -435,8 +435,43 @@ __local_syscall_error: \

 #endif /* __ASSEMBLER__ */

-/* Pointer mangling is not yet supported for ARM.  */
-#define PTR_MANGLE(var) (void) (var)
-#define PTR_DEMANGLE(var) (void) (var)
+/* Pointer mangling support.  */
+#if (defined NOT_IN_libc && defined IS_IN_rtld) || (!defined SHARED && (!defined NOT_IN_libc || defined IS_IN_libpthread))
+# ifdef __ASSEMBLER__
+#  define PTR_MANGLE(dst, src, guard, tmp) \
+  LDST_PCREL(ldr, guard, tmp, C_SYMBOL_NAME(__pointer_chk_guard_local)); \
+  PTR_MANGLE2(dst, src, guard)
+/* Use PTR_MANGLE2 for efficiency if guard is already loaded.  */
+#  define PTR_MANGLE2(dst, src, guard) \
+  eor dst, src, guard
+#  define PTR_DEMANGLE(dst, src, guard, tmp) \
+  PTR_MANGLE (dst, src, guard, tmp)
+#  define PTR_DEMANGLE2(dst, src, guard) \
+  PTR_MANGLE2 (dst, src, guard)
+# else
+extern uintptr_t __pointer_chk_guard_local attribute_relro attribute_hidden;
+#  define PTR_MANGLE(var) \
+  (var) = (__typeof (var)) ((uintptr_t) (var) ^ __pointer_chk_guard_local)
+#  define PTR_DEMANGLE(var)     PTR_MANGLE (var)
+# endif
+#else
+# ifdef __ASSEMBLER__
+#  define PTR_MANGLE(dst, src, guard, tmp) \
+  LDST_GLOBAL(ldr, guard, tmp, C_SYMBOL_NAME(__pointer_chk_guard)); \
+  PTR_MANGLE2(dst, src, guard)
+/* Use PTR_MANGLE2 for efficiency if guard is already loaded.  */
+#  define PTR_MANGLE2(dst, src, guard) \
+  eor dst, src, guard
+#  define PTR_DEMANGLE(dst, src, guard, tmp) \
+  PTR_MANGLE (dst, src, guard, tmp)
+#  define PTR_DEMANGLE2(dst, src, guard) \
+  PTR_MANGLE2 (dst, src, guard)
+# else
+extern uintptr_t __pointer_chk_guard attribute_relro;
+#  define PTR_MANGLE(var) \
+  (var) = (__typeof (var)) ((uintptr_t) (var) ^ __pointer_chk_guard)
+#  define PTR_DEMANGLE(var)     PTR_MANGLE (var)
+# endif
+#endif

 #endif /* linux/arm/sysdep.h */
--
1.8.1.4

Reply | Threaded
Open this post in threaded view
|

Re: [PATCH v3] ARM: Add pointer encryption support.

Joseph Myers
On Mon, 30 Sep 2013, Will Newton wrote:

> 2013-09-27  Will Newton  <[hidden email]>
>
> * sysdeps/arm/__longjmp.S (__longjmp): Demangle fp, sp
> and lr when restoring register values.
> * sysdeps/arm/include/bits/setjmp.h (JMP_BUF_REGLIST): Remove
> sp and lr from list and replace fp with a4.
> * sysdeps/arm/jmpbuf-unwind.h (_jmpbuf_sp): New function.
> (_JMPBUF_UNWINDS_ADJ): Call _jmpbuf_sp.
> * sysdeps/arm/setjmp.S (__sigsetjmp): Mangle fp, sp and lr
> before storing register values.
> * sysdeps/arm/sysdep.h (LDST_GLOBAL): New macro.
> * sysdeps/unix/sysv/linux/arm/sysdep.h (PTR_MANGLE): New macro.
> (PTR_DEMANGLE): Likewise. (PTR_MANGLE2): Likewise.
> (PTR_DEMANGLE2): Likewise.

OK with formatting fixed:

> +#if (defined NOT_IN_libc && defined IS_IN_rtld) || (!defined SHARED && (!defined NOT_IN_libc || defined IS_IN_libpthread))

This line is over 79 columns.

--
Joseph S. Myers
[hidden email]