From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Thu, 2 Nov 2017 00:59:00 -0700
Subject: [PATCH] x86/entry/64: Move SWAPGS into the common IRET-to-usermode
 path
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CVE-2017-5754

All of the code paths that ended up doing IRET to usermode did
SWAPGS immediately beforehand.  Move the SWAPGS into the common
code.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/27fd6f45b7cd640de38fb9066fd0349bcd11f8e1.1509609304.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 8a055d7f411d41755ce30db5bb65b154777c4b78)
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
(cherry picked from commit 62a85594f9be3baeb2495089f1c2980bc497d03b)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
 arch/x86/entry/entry_64.S        | 32 ++++++++++++++------------------
 arch/x86/entry/entry_64_compat.S |  3 +--
 2 files changed, 15 insertions(+), 20 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index e546441fbec3..7c8258e3ad2d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -249,12 +249,14 @@ return_from_SYSCALL_64:
 
 	/*
 	 * Try to use SYSRET instead of IRET if we're returning to
-	 * a completely clean 64-bit userspace context.
+	 * a completely clean 64-bit userspace context.  If we're not,
+	 * go to the slow exit path.
 	 */
 	movq	RCX(%rsp), %rcx
 	movq	RIP(%rsp), %r11
-	cmpq	%rcx, %r11			/* RCX == RIP */
-	jne	opportunistic_sysret_failed
+
+	cmpq	%rcx, %r11	/* SYSRET requires RCX == RIP */
+	jne	swapgs_restore_regs_and_return_to_usermode
 
 	/*
 	 * On Intel CPUs, SYSRET with non-canonical RCX/RIP will #GP
@@ -272,14 +274,14 @@ return_from_SYSCALL_64:
 
 	/* If this changed %rcx, it was not canonical */
 	cmpq	%rcx, %r11
-	jne	opportunistic_sysret_failed
+	jne	swapgs_restore_regs_and_return_to_usermode
 
 	cmpq	$__USER_CS, CS(%rsp)		/* CS must match SYSRET */
-	jne	opportunistic_sysret_failed
+	jne	swapgs_restore_regs_and_return_to_usermode
 
 	movq	R11(%rsp), %r11
 	cmpq	%r11, EFLAGS(%rsp)		/* R11 == RFLAGS */
-	jne	opportunistic_sysret_failed
+	jne	swapgs_restore_regs_and_return_to_usermode
 
 	/*
 	 * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot
@@ -300,12 +302,12 @@ return_from_SYSCALL_64:
 	 * would never get past 'stuck_here'.
 	 */
 	testq	$(X86_EFLAGS_RF|X86_EFLAGS_TF), %r11
-	jnz	opportunistic_sysret_failed
+	jnz	swapgs_restore_regs_and_return_to_usermode
 
 	/* nothing to check for RSP */
 
 	cmpq	$__USER_DS, SS(%rsp)		/* SS must match SYSRET */
-	jne	opportunistic_sysret_failed
+	jne	swapgs_restore_regs_and_return_to_usermode
 
 	/*
 	 * We win! This label is here just for ease of understanding
@@ -318,10 +320,6 @@ syscall_return_via_sysret:
 	movq	RSP(%rsp), %rsp
 	UNWIND_HINT_EMPTY
 	USERGS_SYSRET64
-
-opportunistic_sysret_failed:
-	SWAPGS
-	jmp	restore_regs_and_return_to_usermode
 END(entry_SYSCALL_64)
 
 ENTRY(stub_ptregs_64)
@@ -422,8 +420,7 @@ ENTRY(ret_from_fork)
 	movq	%rsp, %rdi
 	call	syscall_return_slowpath	/* returns with IRQs disabled */
 	TRACE_IRQS_ON			/* user mode is traced as IRQS on */
-	SWAPGS
-	jmp	restore_regs_and_return_to_usermode
+	jmp	swapgs_restore_regs_and_return_to_usermode
 
 1:
 	/* kernel thread */
@@ -611,9 +608,8 @@ GLOBAL(retint_user)
 	mov	%rsp,%rdi
 	call	prepare_exit_to_usermode
 	TRACE_IRQS_IRETQ
-	SWAPGS
 
-GLOBAL(restore_regs_and_return_to_usermode)
+GLOBAL(swapgs_restore_regs_and_return_to_usermode)
 #ifdef CONFIG_DEBUG_ENTRY
 	/* Assert that pt_regs indicates user mode. */
 	testl	$3, CS(%rsp)
@@ -621,6 +617,7 @@ GLOBAL(restore_regs_and_return_to_usermode)
 	ud2
 1:
 #endif
+	SWAPGS
 	RESTORE_EXTRA_REGS
 	RESTORE_C_REGS
 	REMOVE_PT_GPREGS_FROM_STACK 8
@@ -1355,8 +1352,7 @@ ENTRY(nmi)
 	 * Return back to user mode.  We must *not* do the normal exit
 	 * work, because we don't want to enable interrupts.
 	 */
-	SWAPGS
-	jmp	restore_regs_and_return_to_usermode
+	jmp	swapgs_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 2b3a88feaa2b..be745b7a3e3e 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -336,8 +336,7 @@ ENTRY(entry_INT80_compat)
 
 	/* Go back to user mode. */
 	TRACE_IRQS_ON
-	SWAPGS
-	jmp	restore_regs_and_return_to_usermode
+	jmp	swapgs_restore_regs_and_return_to_usermode
 END(entry_INT80_compat)
 
 	ALIGN
-- 
2.14.2

