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From: Andy Lutomirski <luto@kernel.org>
To: X86 ML <x86@kernel.org>
Cc: Borislav Petkov <bpetkov@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>
Subject: [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0()
Date: Thu, 26 Oct 2017 01:26:42 -0700	[thread overview]
Message-ID: <75b2372395f579c20ee6fd53d03eb79c6eea8e81.1509006199.git.luto@kernel.org> (raw)
In-Reply-To: <cover.1509006199.git.luto@kernel.org>
In-Reply-To: <cover.1509006199.git.luto@kernel.org>

This causees the MSR_IA32_SYSENTER_CS write to move out of the
paravirt hook.  This shouldn't affect Xen PV: Xen already ignores
MSR_IA32_SYSENTER_ESP writes.  In any event, Xen doesn't support
vm86() in a useful way.

Note to any potential backporters: This patch won't break lguest, as
lguest didn't have any SYSENTER support at all.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/processor.h |  7 -------
 arch/x86/include/asm/switch_to.h | 11 +++++++++++
 arch/x86/kernel/process_32.c     |  1 +
 arch/x86/kernel/process_64.c     |  2 +-
 arch/x86/kernel/vm86_32.c        |  6 +++++-
 5 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b390ff76e58f..0167e3e35a57 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -520,13 +520,6 @@ static inline void
 native_load_sp0(struct tss_struct *tss, struct thread_struct *thread)
 {
 	tss->x86_tss.sp0 = thread->sp0;
-#ifdef CONFIG_X86_32
-	/* Only happens when SEP is enabled, no need to test "SEP"arately: */
-	if (unlikely(tss->x86_tss.ss1 != thread->sysenter_cs)) {
-		tss->x86_tss.ss1 = thread->sysenter_cs;
-		wrmsr(MSR_IA32_SYSENTER_CS, thread->sysenter_cs, 0);
-	}
-#endif
 }
 
 static inline void native_swapgs(void)
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index fcc5cd387fd1..f3fa19925ae1 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -72,4 +72,15 @@ do {									\
 	((last) = __switch_to_asm((prev), (next)));			\
 } while (0)
 
+#ifdef CONFIG_X86_32
+static inline void refresh_sysenter_cs(struct thread_struct *thread)
+{
+	/* Only happens when SEP is enabled, no need to test "SEP"arately: */
+	if (unlikely(this_cpu_read(cpu_tss.x86_tss.ss1) == thread->sysenter_cs))
+		return;
+
+	this_cpu_write(cpu_tss.x86_tss.ss1, thread->sysenter_cs);
+}
+#endif
+
 #endif /* _ASM_X86_SWITCH_TO_H */
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 11966251cd42..84d6c9f554d0 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -287,6 +287,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 * current_thread_info().
 	 */
 	load_sp0(tss, next);
+	refresh_sysenter_cs(next);  /* in case prev or next is vm86 */
 	this_cpu_write(cpu_current_top_of_stack,
 		       (unsigned long)task_stack_page(next_p) +
 		       THREAD_SIZE);
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 302e7b2572d1..a6ff6d1a0110 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -464,7 +464,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 */
 	this_cpu_write(current_task, next_p);
 
-	/* Reload esp0 and ss1.  This changes current_thread_info(). */
+	/* Reload sp0. */
 	load_sp0(tss, next);
 
 	/*
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
index 7924a5356c8a..5bc1c3ab6287 100644
--- a/arch/x86/kernel/vm86_32.c
+++ b/arch/x86/kernel/vm86_32.c
@@ -54,6 +54,7 @@
 #include <asm/irq.h>
 #include <asm/traps.h>
 #include <asm/vm86.h>
+#include <asm/switch_to.h>
 
 /*
  * Known problems:
@@ -149,6 +150,7 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval)
 	tsk->thread.sp0 = vm86->saved_sp0;
 	tsk->thread.sysenter_cs = __KERNEL_CS;
 	load_sp0(tss, &tsk->thread);
+	refresh_sysenter_cs(&tsk->thread);
 	vm86->saved_sp0 = 0;
 	put_cpu();
 
@@ -368,8 +370,10 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus)
 	/* make room for real-mode segments */
 	tsk->thread.sp0 += 16;
 
-	if (static_cpu_has(X86_FEATURE_SEP))
+	if (static_cpu_has(X86_FEATURE_SEP)) {
 		tsk->thread.sysenter_cs = 0;
+		refresh_sysenter_cs(&tsk->thread);
+	}
 
 	load_sp0(tss, &tsk->thread);
 	put_cpu();
-- 
2.13.6

  parent reply	other threads:[~2017-10-26  8:27 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-10-26  8:26 [PATCH 00/18] Pile o' entry/exit/sp0 changes Andy Lutomirski
2017-10-26  8:26 ` [PATCH 01/18] x86/asm/64: Remove the restore_c_regs_and_iret label Andy Lutomirski
2017-10-26 15:07   ` Borislav Petkov
2017-11-10  6:08   ` [01/18] " kemi
2017-10-26  8:26 ` [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths Andy Lutomirski
2017-10-27 18:05   ` Dave Hansen
2017-11-01 11:34     ` Andy Lutomirski
2017-10-27 20:04   ` Borislav Petkov
2017-11-01 11:32     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 03/18] x86/asm/64: Move SWAPGS into the common iret-to-usermode path Andy Lutomirski
2017-10-26 13:52   ` Brian Gerst
2017-10-26 14:13     ` Dave Hansen
2017-10-26 14:28       ` Borislav Petkov
2017-10-27 15:44         ` Andy Lutomirski
2017-10-27 18:08   ` Dave Hansen
2017-10-26  8:26 ` [PATCH 04/18] x86/asm/64: Simplify reg restore code in the standard IRET paths Andy Lutomirski
2017-10-26  8:26 ` [PATCH 05/18] x86/asm/64: Shrink paranoid_exit_restore and make labels local Andy Lutomirski
2017-10-27 20:07   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 06/18] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 07/18] x86/asm/64: Merge the fast and slow SYSRET paths Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-11-01 11:29     ` Andy Lutomirski
2017-11-01 12:35       ` Borislav Petkov
2017-11-01 17:26         ` Thomas Gleixner
2017-11-01 17:25   ` Brian Gerst
2017-11-01 20:35     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 08/18] xen: add xen nmi trap entry Andy Lutomirski
2017-10-26  8:26 ` [PATCH 09/18] x86/asm/64: De-Xen-ify our NMI code Andy Lutomirski
2017-10-26  8:41   ` Juergen Gross
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` Andy Lutomirski [this message]
2017-10-26 18:00   ` [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0() Brian Gerst
2017-10-27 13:51   ` Thomas Gleixner
2017-10-27 15:50     ` Andy Lutomirski
2017-10-27 20:11   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 11/18] x86/asm/64: Pass sp0 directly to load_sp0() Andy Lutomirski
2017-10-27 20:12   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 12/18] x86/asm: Add task_top_of_stack() to find the top of a task's stack Andy Lutomirski
2017-10-26  8:26 ` [PATCH 13/18] x86/xen/64: Clean up SP code in cpu_initialize_context() Andy Lutomirski
2017-10-26  8:43   ` Juergen Gross
2017-10-26  8:26 ` [PATCH 14/18] x86/boot/64: Stop initializing TSS.sp0 at boot Andy Lutomirski
2017-10-27 18:21   ` Dave Hansen
2017-10-28  8:10     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 15/18] x86/asm/64: Remove all remaining direct thread_struct::sp0 reads Andy Lutomirski
2017-11-01 10:08   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 16/18] x86/boot/32: Fix cpu_current_top_of_stack initialization at boot Andy Lutomirski
2017-11-01 10:18   ` Borislav Petkov
2017-10-26  8:26 ` [PATCH 17/18] x86/asm/64: Remove thread_struct::sp0 Andy Lutomirski
2017-10-28  0:52   ` Brian Gerst
2017-11-01 10:23   ` Borislav Petkov
2017-11-01 10:40     ` Andy Lutomirski
2017-10-26  8:26 ` [PATCH 18/18] x86/traps: Use a new on_thread_stack() helper to clean up an assertion Andy Lutomirski
2017-11-01 10:31   ` Borislav Petkov
2017-11-01 10:45     ` Andy Lutomirski
2017-10-26 15:55 ` [PATCH 00/18] Pile o' entry/exit/sp0 changes Linus Torvalds
2017-10-28  7:31   ` Andy Lutomirski

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