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Subject[tip:x86/asm] x86/asm/entry/64: Use common code for rt_sigreturn( ) epilogue
Commit-ID:  31f0119b817f6474a7b4c48fed7588af1b62c543
Gitweb: http://git.kernel.org/tip/31f0119b817f6474a7b4c48fed7588af1b62c543
Author: Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Tue, 7 Apr 2015 22:43:37 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 9 Apr 2015 10:31:24 +0200

x86/asm/entry/64: Use common code for rt_sigreturn() epilogue

Similarly to stub_execve, we can reuse the epilogue in
stub_rt_sigreturn() and stub_x32_rt_sigreturn().

Add a comment explaining why we can't eliminage SAVE_EXTRA_REGS
here.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1428439424-7258-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/entry_64.S | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 3197f41..5252e60 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -527,12 +527,21 @@ END(stub_execveat)
*/
ENTRY(stub_rt_sigreturn)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
+ DEFAULT_FRAME 0, 8
+ /*
+ * SAVE_EXTRA_REGS result is not normally needed:
+ * sigreturn overwrites all pt_regs->GPREGS.
+ * But sigreturn can fail (!), and there is no easy way to detect that.
+ * To make sure RESTORE_EXTRA_REGS doesn't restore garbage on error,
+ * we SAVE_EXTRA_REGS here.
+ */
+ SAVE_EXTRA_REGS 8
call sys_rt_sigreturn
- movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
+return_from_stub:
+ addq $8, %rsp
+ CFI_ADJUST_CFA_OFFSET -8
RESTORE_EXTRA_REGS
+ movq %rax,RAX(%rsp)
jmp int_ret_from_sys_call
CFI_ENDPROC
END(stub_rt_sigreturn)
@@ -540,13 +549,10 @@ END(stub_rt_sigreturn)
#ifdef CONFIG_X86_X32_ABI
ENTRY(stub_x32_rt_sigreturn)
CFI_STARTPROC
- addq $8, %rsp
- DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
+ DEFAULT_FRAME 0, 8
+ SAVE_EXTRA_REGS 8
call sys32_x32_rt_sigreturn
- movq %rax,RAX(%rsp) # fixme, this could be done at the higher layer
- RESTORE_EXTRA_REGS
- jmp int_ret_from_sys_call
+ jmp return_from_stub
CFI_ENDPROC
END(stub_x32_rt_sigreturn)


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