[PATCH] [BZ #18134] x86-64 ld.so doesn't preserve bound registers

[H.J. Lu]

We need to add a BND prefix before indirect branch at the end of
_dl_runtime_resolve to preserve bound registers.

Tested on x32, x86-64 Haswell and x86-64 Skylake. I will check it into
master shortly and backport it to 2.21 branch.

Igor, this patch doesn't fix _dl_runtime_profile.  Can you take care of
_dl_runtime_profile?

Thanks.


H.J.
---
	[BZ #18134]
	* sysdeps/x86_64/dl-trampoline.S (PRESERVE_BND_REGS_PREFIX): New.
	(_dl_runtime_resolve): Add a BND prefix before indirect branch.
---
 sysdeps/x86_64/dl-trampoline.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sysdeps/x86_64/dl-trampoline.S b/sysdeps/x86_64/dl-trampoline.S
index 394441d..5f9b35d 100644
--- a/sysdeps/x86_64/dl-trampoline.S
+++ b/sysdeps/x86_64/dl-trampoline.S
@@ -30,6 +30,7 @@
 /* X32 saves RCX, RDX, RSI, RDI, R8 and R9 plus RAX.  */
 # define REGISTER_SAVE_AREA	(8 * 7)
 # define REGISTER_SAVE_RAX	0
+# define PRESERVE_BND_REGS_PREFIX
 #else
 /* X86-64 saves RCX, RDX, RSI, RDI, R8 and R9 plus RAX as well as BND0,
    BND1, BND2, BND3.  */
@@ -40,6 +41,11 @@
 # define REGISTER_SAVE_BND2	(REGISTER_SAVE_BND1 + 16)
 # define REGISTER_SAVE_BND3	(REGISTER_SAVE_BND2 + 16)
 # define REGISTER_SAVE_RAX	(REGISTER_SAVE_BND3 + 16)
+# ifdef HAVE_MPX_SUPPORT
+#  define PRESERVE_BND_REGS_PREFIX bnd
+# else
+#  define PRESERVE_BND_REGS_PREFIX .byte 0xf2
+# endif
 #endif
 #define REGISTER_SAVE_RCX	(REGISTER_SAVE_RAX + 8)
 #define REGISTER_SAVE_RDX	(REGISTER_SAVE_RCX + 8)
@@ -112,6 +118,8 @@ _dl_runtime_resolve:
 	# Adjust stack(PLT did 2 pushes)
 	addq $(REGISTER_SAVE_AREA + 16), %rsp
 	cfi_adjust_cfa_offset(-(REGISTER_SAVE_AREA + 16))
+	# Preserve bound registers.
+	PRESERVE_BND_REGS_PREFIX
 	jmp *%r11		# Jump to function address.
 	cfi_endproc
 	.size _dl_runtime_resolve, .-_dl_runtime_resolve
-- 
1.9.3