Patch "x86/entry/64: Move SWAPGS into the common IRET-to-usermode path" has been added to the 4.14-stable tree

This is a note to let you know that I've just added the patch titled

x86/entry/64: Move SWAPGS into the common IRET-to-usermode path

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-entry-64-move-swapgs-into-the-common-iret-to-usermode-path.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andy Lutomirski <[email protected]>
Date: Thu, 2 Nov 2017 00:59:00 -0700
Subject: x86/entry/64: Move SWAPGS into the common IRET-to-usermode path

From: Andy Lutomirski <[email protected]>

commit 8a055d7f411d41755ce30db5bb65b154777c4b78 upstream.

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

---
 arch/x86/entry/entry_64.S        |   32 ++++++++++++++------------------
 arch/x86/entry/entry_64_compat.S |    3 +--
 2 files changed, 15 insertions(+), 20 deletions(-)

@@ -250,12 +250,14 @@ 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

@@ -273,14 +275,14 @@ 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

@@ -301,12 +303,12 @@ 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

@@ -319,10 +321,6 @@ 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)

@@ -423,8 +421,7 @@ 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 */

@@ -612,9 +609,8 @@ 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)

@@ -622,6 +618,7 @@ GLOBAL(restore_regs_and_return_to_usermo
 	ud2
 1:
 #endif
+	SWAPGS
 	RESTORE_EXTRA_REGS
 	RESTORE_C_REGS
 	REMOVE_PT_GPREGS_FROM_STACK 8

@@ -1343,8 +1340,7 @@ 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:
 	/*

@@ -337,8 +337,7 @@ 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)
 
 ENTRY(stub32_clone)

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/x86-entry-64-simplify-reg-restore-code-in-the-standard-iret-paths.patch queue-4.14/x86-cpufeatures-fix-various-details-in-the-feature-definitions.patch queue-4.14/x86-entry-64-move-the-ist-stacks-into-struct-cpu_entry_area.patch queue-4.14/x86-dumpstack-add-get_stack_info-support-for-the-sysenter-stack.patch queue-4.14/x86-asm-don-t-use-the-confusing-.ifeq-directive.patch queue-4.14/selftests-x86-ldt_gdt-add-infrastructure-to-test-set_thread_area.patch queue-4.14/x86-entry-remap-the-tss-into-the-cpu-entry-area.patch queue-4.14/x86-entry-64-paravirt-use-paravirt-safe-macro-to-access-eflags.patch queue-4.14/x86-mm-fixmap-generalize-the-gdt-fixmap-mechanism-introduce-struct-cpu_entry_area.patch queue-4.14/x86-paravirt-dont-patch-flush_tlb_single.patch queue-4.14/x86-dumpstack-handle-stack-overflow-on-all-stacks.patch queue-4.14/x86-entry-64-use-pop-instead-of-movq-in-syscall_return_via_sysret.patch queue-4.14/x86-entry-64-return-to-userspace-from-the-trampoline-stack.patch queue-4.14/x86-paravirt-provide-a-way-to-check-for-hypervisors.patch queue-4.14/xen-x86-entry-64-add-xen-nmi-trap-entry.patch queue-4.14/x86-entry-64-remove-the-restore_c_regs_and_iret-label.patch queue-4.14/x86-entry-64-create-a-per-cpu-syscall-entry-trampoline.patch queue-4.14/x86-entry-64-remove-the-restore_..._regs-infrastructure.patch queue-4.14/x86-xen-64-x86-entry-64-clean-up-sp-code-in-cpu_initialize_context.patch queue-4.14/x86-entry-add-task_top_of_stack-to-find-the-top-of-a-task-s-stack.patch queue-4.14/x86-entry-64-remove-all-remaining-direct-thread_struct-sp0-reads.patch queue-4.14/x86-boot-relocate-definition-of-the-initial-state-of-cr0.patch queue-4.14/x86-entry-64-stop-initializing-tss.sp0-at-boot.patch queue-4.14/x86-entry-64-de-xen-ify-our-nmi-code.patch queue-4.14/objtool-don-t-report-end-of-section-error-after-an-empty-unwind-hint.patch queue-4.14/x86-entry-64-pass-sp0-directly-to-load_sp0.patch queue-4.14/x86-entry-64-use-a-per-cpu-trampoline-stack-for-idt-entries.patch queue-4.14/x86-entry-64-move-swapgs-into-the-common-iret-to-usermode-path.patch queue-4.14/x86-entry-64-shorten-test-instructions.patch queue-4.14/x86-cpufeature-add-user-mode-instruction-prevention-definitions.patch queue-4.14/x86-cpufeatures-make-cpu-bugs-sticky.patch queue-4.14/x86-espfix-64-stop-assuming-that-pt_regs-is-on-the-entry-stack.patch queue-4.14/x86-traps-use-a-new-on_thread_stack-helper-to-clean-up-an-assertion.patch queue-4.14/x86-xen-fix-xen-head-elf-annotations.patch queue-4.14/x86-entry-64-remove-thread_struct-sp0.patch queue-4.14/x86-entry-move-sysenter_stack-to-the-beginning-of-struct-tss_struct.patch queue-4.14/x86-entry-64-allocate-and-enable-the-sysenter-stack.patch queue-4.14/x86-unwinder-orc-dont-bail-on-stack-overflow.patch queue-4.14/x86-head-fix-head-elf-function-annotations.patch queue-4.14/selftests-x86-ldt_gdt-run-most-existing-ldt-test-cases-against-the-gdt-as-well.patch queue-4.14/x86-entry-32-pull-the-msr_ia32_sysenter_cs-update-code-out-of-native_load_sp0.patch queue-4.14/x86-entry-64-split-the-iret-to-user-and-iret-to-kernel-paths.patch queue-4.14/x86-entry-64-shrink-paranoid_exit_restore-and-make-labels-local.patch queue-4.14/x86-head-add-unwind-hint-annotations.patch queue-4.14/x86-head-remove-unused-bad_address-code.patch queue-4.14/x86-xen-add-unwind-hint-annotations.patch queue-4.14/x86-kasan-64-teach-kasan-about-the-cpu_entry_area.patch queue-4.14/x86-head-remove-confusing-comment.patch queue-4.14/x86-entry-64-remove-the-sysenter-stack-canary.patch queue-4.14/x86-mm-kasan-don-t-use-vmemmap_populate-to-initialize-shadow.patch queue-4.14/x86-entry-gdt-put-per-cpu-gdt-remaps-in-ascending-order.patch queue-4.14/x86-entry-fix-assumptions-that-the-hw-tss-is-at-the-beginning-of-cpu_tss.patch queue-4.14/x86-cpufeatures-re-tabulate-the-x86_feature-definitions.patch queue-4.14/x86-entry-32-fix-cpu_current_top_of_stack-initialization-at-boot.patch queue-4.14/ptrace-x86-make-user_64bit_mode-available-to-32-bit-builds.patch queue-4.14/x86-entry-64-make-cpu_entry_area.tss-read-only.patch queue-4.14/x86-mm-relocate-page-fault-error-codes-to-traps.h.patch queue-4.14/x86-unwinder-handle-stack-overflows-more-gracefully.patch queue-4.14/x86-entry-64-use-pop-instead-of-mov-to-restore-regs-on-nmi-return.patch queue-4.14/x86-irq-64-print-the-offending-ip-in-the-stack-overflow-warning.patch queue-4.14/x86-entry-clean-up-the-sysenter_stack-code.patch queue-4.14/x86-entry-64-merge-the-fast-and-slow-sysret-paths.patch queue-4.14/x86-entry-64-separate-cpu_current_top_of_stack-from-tss.sp0.patch queue-4.14/x86-boot-annotate-verify_cpu-as-a-callable-function.patch queue-4.14/x86-irq-remove-an-old-outdated-comment-about-context-tracking-races.patch