AArch64: use movz/movk instead of literal pools in start.S

eXecute-Only Memory (XOM) is a protection mechanism against some ROP
attacks. XOM sets the code as executable and unreadable, so the access
to any data, like literal pools, in the code section causes the fault
with XOM. The compiler can disable literal pools for C source files,
but not for assembly files, so I use movz/movk instead of literal pools
in start.S for XOM.

I add MOVL macro with movz/movk instructions like movl pseudo-instruction
in armasm, and use the macro instead of literal pools.

	* sysdeps/aarch64/start.S: Use MOVL instead of literal pools.
	* sysdeps/aarch64/sysdep.h (MOVL): Add MOVL macro.

diff --git a/ChangeLog b/ChangeLog
index 48a8b67619660f361420822a48d27a06cdce7b1e..1d60d1264390fe9618d30111505e861e249c93d6 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2017-09-18  Wang Boshi  <wangboshi@huawei.com>  (tiny change)
+
+       * sysdeps/aarch64/start.S: Use MOVL instead of literal pools.
+       * sysdeps/aarch64/sysdep.h (MOVL): Add MOVL macro.
+
 2017-09-17  Samuel Thibault  <samuel.thibault@ens-lyon.org>
 
        * io/read.c (read): Add libc_hidden_weak.

diff --git a/sysdeps/aarch64/start.S b/sysdeps/aarch64/start.S
index df1c642c12097a3344cc4c557d409b443e33551d..c20433ad7334882b3ec0d933c5f10c20f87f6695 100644 (file)
--- a/sysdeps/aarch64/start.S
+++ b/sysdeps/aarch64/start.S
@@ -71,9 +71,9 @@ _start:
        ldr     PTR_REG (4), [x4, #:got_lo12:__libc_csu_fini]
 #else
        /* Set up the other arguments in registers */
-       ldr     PTR_REG (0), =main
-       ldr     PTR_REG (3), =__libc_csu_init
-       ldr     PTR_REG (4), =__libc_csu_fini
+       MOVL (0, main)
+       MOVL (3, __libc_csu_init)
+       MOVL (4, __libc_csu_fini)
 #endif
 
        /* __libc_start_main (main, argc, argv, init, fini, rtld_fini,

diff --git a/sysdeps/aarch64/sysdep.h b/sysdeps/aarch64/sysdep.h
index a749a707ecde9a26aa5d55e9fee55ea70470b29d..aba18de4d75e82e374e1e131ce08a7d40fe8ba99 100644 (file)
--- a/sysdeps/aarch64/sysdep.h
+++ b/sysdeps/aarch64/sysdep.h
@@ -137,6 +137,20 @@
        ldr     PTR_REG (T), [x##T, #:got_lo12:EXPR];   \
        OP      PTR_REG (R), [x##T];
 
+/* Load an immediate into R.
+   Note R is a register number and not a register name.  */
+#ifdef __LP64__
+# define MOVL(R, NAME)                                 \
+       movz    PTR_REG (R), #:abs_g3:NAME;             \
+       movk    PTR_REG (R), #:abs_g2_nc:NAME;          \
+       movk    PTR_REG (R), #:abs_g1_nc:NAME;          \
+       movk    PTR_REG (R), #:abs_g0_nc:NAME;
+#else
+# define MOVL(R, NAME)                                 \
+       movz    PTR_REG (R), #:abs_g1:NAME;             \
+       movk    PTR_REG (R), #:abs_g0_nc:NAME;
+#endif
+
 /* Since C identifiers are not normally prefixed with an underscore
    on this system, the asm identifier `syscall_error' intrudes on the
    C name space.  Make sure we use an innocuous name.  */