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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.
This commit is contained in:
Wang Boshi 2017-09-15 17:53:23 +01:00 committed by Szabolcs Nagy
parent 1c6d89e9a4
commit 6cd380dd36
3 changed files with 22 additions and 3 deletions
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5
ChangeLog
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@ -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.

6
sysdeps/aarch64/start.S
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@ -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,

14
sysdeps/aarch64/sysdep.h
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@ -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. */