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authorWang Boshi <wangboshi@huawei.com>2017-09-15 17:53:23 +0100
committerSzabolcs Nagy <szabolcs.nagy@arm.com>2017-09-18 18:15:47 +0100
commit6cd380dd366d728da9f579eeb9f7f4c47f48e474 (patch)
treea6c1ac8110060c1bc059697def0bc5b2cb9e66b7
parent1c6d89e9a40302430d5986a09c7cf7594b93143c (diff)
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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.
-rw-r--r--ChangeLog5
-rw-r--r--sysdeps/aarch64/start.S6
-rw-r--r--sysdeps/aarch64/sysdep.h14
3 files changed, 22 insertions, 3 deletions
diff --git a/ChangeLog b/ChangeLog
index 48a8b67619..1d60d12643 100644
--- 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 df1c642c12..c20433ad73 100644
--- 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 a749a707ec..aba18de4d7 100644
--- 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.  */