linux-kernel - [RFC 02/17] x86/asm/64: Split the iret-to-user and iret-to-kernel paths

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Date:   Wed,  6 Sep 2017 14:36:47 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [RFC 02/17] x86/asm/64: Split the iret-to-user and iret-to-kernel paths

These code paths will diverge soon.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S        | 20 +++++++++++---------
 arch/x86/entry/entry_64_compat.S |  2 +-
 arch/x86/kernel/head_64.S        |  2 +-
 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index a0ebeeb9d12f..34156d50c3d6 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -315,7 +315,7 @@ syscall_return_via_sysret:
 
 opportunistic_sysret_failed:
 	SWAPGS
-	jmp	restore_regs_and_iret
+	jmp	restore_regs_and_return_to_usermode
 END(entry_SYSCALL_64)
 
 ENTRY(stub_ptregs_64)
@@ -412,7 +412,7 @@ ENTRY(ret_from_fork)
 	call	syscall_return_slowpath	/* returns with IRQs disabled */
 	TRACE_IRQS_ON			/* user mode is traced as IRQS on */
 	SWAPGS
-	jmp	restore_regs_and_iret
+	jmp	restore_regs_and_return_to_usermode
 
 1:
 	/* kernel thread */
@@ -524,7 +524,13 @@ GLOBAL(retint_user)
 	call	prepare_exit_to_usermode
 	TRACE_IRQS_IRETQ
 	SWAPGS
-	jmp	restore_regs_and_iret
+
+GLOBAL(restore_regs_and_return_to_usermode)
+	RESTORE_EXTRA_REGS
+	RESTORE_C_REGS
+	REMOVE_PT_GPREGS_FROM_STACK 8
+	INTERRUPT_RETURN
+
 
 /* Returning to kernel space */
 retint_kernel:
@@ -544,11 +550,7 @@ retint_kernel:
 	 */
 	TRACE_IRQS_IRETQ
 
-/*
- * At this label, code paths which return to kernel and to user,
- * which come from interrupts/exception and from syscalls, merge.
- */
-GLOBAL(restore_regs_and_iret)
+GLOBAL(restore_regs_and_return_to_kernel)
 	RESTORE_EXTRA_REGS
 	RESTORE_C_REGS
 	REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1264,7 +1266,7 @@ ENTRY(nmi)
 	 * work, because we don't want to enable interrupts.
 	 */
 	SWAPGS
-	jmp	restore_regs_and_iret
+	jmp	restore_regs_and_return_to_usermode
 
 .Lnmi_from_kernel:
 	/*
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 5314d7b8e5ad..e4ab8ffa94b1 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -338,7 +338,7 @@ ENTRY(entry_INT80_compat)
 	/* Go back to user mode. */
 	TRACE_IRQS_ON
 	SWAPGS
-	jmp	restore_regs_and_iret
+	jmp	restore_regs_and_return_to_usermode
 END(entry_INT80_compat)
 
 	ALIGN
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 6225550883df..63fa56ead56e 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -310,7 +310,7 @@ early_idt_handler_common:
 
 20:
 	decl early_recursion_flag(%rip)
-	jmp restore_regs_and_iret
+	jmp restore_regs_and_return_to_kernel
 ENDPROC(early_idt_handler_common)
 
 	__INITDATA
-- 
2.13.5