linux-kernel - [PATCH v2 02/20] x86/asm/64: Split the iret-to-user and iret-to-kernel paths

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Message-Id: <dccf8c7b3750199b4b30383c812d4e2931811509.1509609304.git.luto@kernel.org>
Date:   Thu,  2 Nov 2017 00:58:59 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     X86 ML <x86@...nel.org>
Cc:     Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v2 02/20] 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        | 34 +++++++++++++++++++++++++---------
 arch/x86/entry/entry_64_compat.S |  2 +-
 arch/x86/kernel/head_64.S        |  2 +-
 3 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index afe1f403fa0e..07fe816f0d28 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -321,7 +321,7 @@ 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)
@@ -423,7 +423,7 @@ 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 */
@@ -612,7 +612,20 @@ GLOBAL(retint_user)
 	call	prepare_exit_to_usermode
 	TRACE_IRQS_IRETQ
 	SWAPGS
-	jmp	restore_regs_and_iret
+
+GLOBAL(restore_regs_and_return_to_usermode)
+#ifdef CONFIG_DEBUG_ENTRY
+	/* Assert that pt_regs indicates user mode. */
+	testl	$3, CS(%rsp)
+	jnz	1f
+	ud2
+1:
+#endif
+	RESTORE_EXTRA_REGS
+	RESTORE_C_REGS
+	REMOVE_PT_GPREGS_FROM_STACK 8
+	INTERRUPT_RETURN
+
 
 /* Returning to kernel space */
 retint_kernel:
@@ -632,11 +645,14 @@ 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)
+#ifdef CONFIG_DEBUG_ENTRY
+	/* Assert that pt_regs indicates kernel mode. */
+	testl	$3, CS(%rsp)
+	jz	1f
+	ud2
+1:
+#endif
 	RESTORE_EXTRA_REGS
 	RESTORE_C_REGS
 	REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1327,7 +1343,7 @@ 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 e26c25ca7756..9ca014a99968 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -337,7 +337,7 @@ 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)
 
 ENTRY(stub32_clone)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 513cbb012ecc..0b01a105251b 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -326,7 +326,7 @@ 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
-- 
2.13.6