x86/asm/entry/32: Open-code CLEAR_RREGS

This macro is small, has only four callsites, and one of them is
slightly different using a conditional parameter.

A few saved lines aren't worth the resulting obfuscation.

Generated machine code is identical.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
[ Added comments. ]
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1433271842-9139-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/ia32entry.S

@@ -29,15 +29,6 @@
 
 	.section .entry.text, "ax"
 
-	/* clobbers %rax */
-	.macro  CLEAR_RREGS _r9=rax
-	xorl 	%eax,%eax
-	movq	%rax,R11(%rsp)
-	movq	%rax,R10(%rsp)
-	movq	%\_r9,R9(%rsp)
-	movq	%rax,R8(%rsp)
-	.endm
-
 	/*
 	 * Reload arg registers from stack in case ptrace changed them.
 	 * We don't reload %eax because syscall_trace_enter() returned
@@ -243,7 +234,11 @@ sysexit_from_sys_call:
 	TRACE_IRQS_OFF
 	testl %edi, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
 	jz \exit
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	jmp int_with_check
 	.endm
 
@@ -267,7 +262,11 @@ sysenter_tracesys:
 	jz	sysenter_auditsys
 #endif
 	SAVE_EXTRA_REGS
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	movq	%rsp,%rdi        /* &pt_regs -> arg1 */
 	call	syscall_trace_enter
 	LOAD_ARGS32  /* reload args from stack in case ptrace changed it */
@@ -407,7 +406,11 @@ cstar_tracesys:
 #endif
 	xchgl %r9d,%ebp
 	SAVE_EXTRA_REGS
-	CLEAR_RREGS r9
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%r9,  R9(%rsp)
+	movq	%rax, R8(%rsp)
 	movq %rsp,%rdi        /* &pt_regs -> arg1 */
 	call syscall_trace_enter
 	LOAD_ARGS32 1	/* reload args from stack in case ptrace changed it */
@@ -422,7 +425,11 @@ ia32_badarg:
 	jmp ia32_sysret
 
 ia32_ret_from_sys_call:
-	CLEAR_RREGS
+	xorl	%eax, %eax	/* do not leak kernel information */
+	movq	%rax, R11(%rsp)
+	movq	%rax, R10(%rsp)
+	movq	%rax, R9(%rsp)
+	movq	%rax, R8(%rsp)
 	jmp int_ret_from_sys_call
 
 /*