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From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Willy Tarreau <w@1wt.eu>, Juergen Gross <jgross@suse.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: [patch V3 12/20] x86/ioperm: Move TSS bitmap update to exit to user work
Date: Wed, 13 Nov 2019 21:42:52 +0100
Message-ID: <20191113210104.882617091@linutronix.de> (raw)
In-Reply-To: <20191113204240.767922595@linutronix.de>

From: Thomas Gleixner <tglx@linutronix.de>

There is no point to update the TSS bitmap for tasks which use I/O bitmaps
on every context switch. It's enough to update it right before exiting to
user space.

That reduces the context switch bitmap handling to invalidating the io
bitmap base offset in the TSS when the outgoing task has TIF_IO_BITMAP
set. The invaldiation is done on purpose when a task with an IO bitmap
switches out to prevent any possible leakage of an activated IO bitmap.

It also removes the requirement to update the tasks bitmap atomically in
ioperm().

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
V3: Updated comment and changelog to clarify the invalidation logic
    Removed _TIF_IO_BITMAP from _TIF_WORK_CTXSW_NEXT as it is only
    required for the outgoing task.

V2: New patch
---
 arch/x86/entry/common.c            |    4 ++
 arch/x86/include/asm/io_bitmap.h   |    2 +
 arch/x86/include/asm/thread_info.h |    9 +++--
 arch/x86/kernel/ioport.c           |   25 ++-------------
 arch/x86/kernel/process.c          |   59 ++++++++++++++++++++++++-------------
 5 files changed, 54 insertions(+), 45 deletions(-)

--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -33,6 +33,7 @@
 #include <asm/cpufeature.h>
 #include <asm/fpu/api.h>
 #include <asm/nospec-branch.h>
+#include <asm/io_bitmap.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
@@ -196,6 +197,9 @@ static void exit_to_usermode_loop(struct
 	/* Reload ti->flags; we may have rescheduled above. */
 	cached_flags = READ_ONCE(ti->flags);
 
+	if (unlikely(cached_flags & _TIF_IO_BITMAP))
+		tss_update_io_bitmap();
+
 	fpregs_assert_state_consistent();
 	if (unlikely(cached_flags & _TIF_NEED_FPU_LOAD))
 		switch_fpu_return();
--- a/arch/x86/include/asm/io_bitmap.h
+++ b/arch/x86/include/asm/io_bitmap.h
@@ -11,4 +11,6 @@ struct io_bitmap {
 	unsigned long	bitmap[IO_BITMAP_LONGS];
 };
 
+void tss_update_io_bitmap(void);
+
 #endif
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -143,8 +143,8 @@ struct thread_info {
 	 _TIF_NOHZ)
 
 /* flags to check in __switch_to() */
-#define _TIF_WORK_CTXSW_BASE						\
-	(_TIF_IO_BITMAP|_TIF_NOCPUID|_TIF_NOTSC|_TIF_BLOCKSTEP|		\
+#define _TIF_WORK_CTXSW_BASE					\
+	(_TIF_NOCPUID | _TIF_NOTSC | _TIF_BLOCKSTEP |		\
 	 _TIF_SSBD | _TIF_SPEC_FORCE_UPDATE)
 
 /*
@@ -156,8 +156,9 @@ struct thread_info {
 # define _TIF_WORK_CTXSW	(_TIF_WORK_CTXSW_BASE)
 #endif
 
-#define _TIF_WORK_CTXSW_PREV (_TIF_WORK_CTXSW|_TIF_USER_RETURN_NOTIFY)
-#define _TIF_WORK_CTXSW_NEXT (_TIF_WORK_CTXSW)
+#define _TIF_WORK_CTXSW_PREV	(_TIF_WORK_CTXSW| _TIF_USER_RETURN_NOTIFY | \
+				 _TIF_IO_BITMAP)
+#define _TIF_WORK_CTXSW_NEXT	(_TIF_WORK_CTXSW)
 
 #define STACK_WARN		(THREAD_SIZE/8)
 
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -21,9 +21,8 @@ static atomic64_t io_bitmap_sequence;
  */
 long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 {
-	unsigned int i, max_long, bytes, bytes_updated;
 	struct thread_struct *t = &current->thread;
-	struct tss_struct *tss;
+	unsigned int i, max_long;
 	struct io_bitmap *iobm;
 
 	if ((from + num <= from) || (from + num > IO_BITMAP_BITS))
@@ -50,10 +49,9 @@ long ksys_ioperm(unsigned long from, uns
 	}
 
 	/*
-	 * Update the bitmap and the TSS copy with preemption disabled to
-	 * prevent a race against context switch.
+	 * Update the tasks bitmap. The update of the TSS bitmap happens on
+	 * exit to user mode. So this needs no protection.
 	 */
-	preempt_disable();
 	if (turn_on)
 		bitmap_clear(iobm->bitmap, from, num);
 	else
@@ -69,11 +67,8 @@ long ksys_ioperm(unsigned long from, uns
 			max_long = i;
 	}
 
-	bytes = (max_long + 1) * sizeof(unsigned long);
-	bytes_updated = max(bytes, t->io_bitmap->max);
+	iobm->max = (max_long + 1) * sizeof(unsigned long);
 
-	/* Update the thread data */
-	iobm->max = bytes;
 	/* Update the sequence number to force an update in switch_to() */
 	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
 
@@ -85,18 +80,6 @@ long ksys_ioperm(unsigned long from, uns
 	t->io_bitmap = iobm;
 	set_thread_flag(TIF_IO_BITMAP);
 
-	/* Update the TSS */
-	tss = this_cpu_ptr(&cpu_tss_rw);
-	memcpy(tss->io_bitmap.bitmap, iobm->bitmap, bytes_updated);
-	/* Store the new end of the zero bits */
-	tss->io_bitmap.prev_max = bytes;
-	/* Make the bitmap base in the TSS valid */
-	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
-	/* Make sure the TSS limit covers the I/O bitmap. */
-	refresh_tss_limit();
-
-	preempt_enable();
-
 	return 0;
 }
 
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -354,8 +354,34 @@ void arch_setup_new_exec(void)
 	}
 }
 
-static void switch_to_update_io_bitmap(struct tss_struct *tss,
-				       struct io_bitmap *iobm)
+static inline void tss_invalidate_io_bitmap(struct tss_struct *tss)
+{
+	/*
+	 * Invalidate the I/O bitmap by moving io_bitmap_base outside the
+	 * TSS limit so any subsequent I/O access from user space will
+	 * trigger a #GP.
+	 *
+	 * This is correct even when VMEXIT rewrites the TSS limit
+	 * to 0x67 as the only requirement is that the base points
+	 * outside the limit.
+	 */
+	tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+}
+
+static inline void switch_to_bitmap(unsigned long tifp)
+{
+	/*
+	 * Invalidate I/O bitmap if the previous task used it. This prevents
+	 * any possible leakage of an active I/O bitmap.
+	 *
+	 * If the next task has an I/O bitmap it will handle it on exit to
+	 * user mode.
+	 */
+	if (tifp & _TIF_IO_BITMAP)
+		tss_invalidate_io_bitmap(this_cpu_ptr(&cpu_tss_rw));
+}
+
+static void tss_copy_io_bitmap(struct tss_struct *tss, struct io_bitmap *iobm)
 {
 	/*
 	 * Copy at least the byte range of the incoming tasks bitmap which
@@ -376,13 +402,15 @@ static void switch_to_update_io_bitmap(s
 	tss->io_bitmap.prev_sequence = iobm->sequence;
 }
 
-static inline void switch_to_bitmap(struct thread_struct *next,
-				    unsigned long tifp, unsigned long tifn)
+/**
+ * tss_update_io_bitmap - Update I/O bitmap before exiting to usermode
+ */
+void tss_update_io_bitmap(void)
 {
 	struct tss_struct *tss = this_cpu_ptr(&cpu_tss_rw);
 
-	if (tifn & _TIF_IO_BITMAP) {
-		struct io_bitmap *iobm = next->io_bitmap;
+	if (test_thread_flag(TIF_IO_BITMAP)) {
+		struct io_bitmap *iobm = current->thread.io_bitmap;
 
 		/*
 		 * Only copy bitmap data when the sequence number
@@ -390,7 +418,7 @@ static inline void switch_to_bitmap(stru
 		 * task.
 		 */
 		if (tss->io_bitmap.prev_sequence != iobm->sequence)
-			switch_to_update_io_bitmap(tss, iobm);
+			tss_copy_io_bitmap(tss, iobm);
 
 		/* Enable the bitmap */
 		tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_VALID;
@@ -403,18 +431,8 @@ static inline void switch_to_bitmap(stru
 		 * limit.
 		 */
 		refresh_tss_limit();
-	} else if (tifp & _TIF_IO_BITMAP) {
-		/*
-		 * Do not touch the bitmap. Let the next bitmap using task
-		 * deal with the mess. Just make the io_bitmap_base invalid
-		 * by moving it outside the TSS limit so any subsequent I/O
-		 * access from user space will trigger a #GP.
-		 *
-		 * This is correct even when VMEXIT rewrites the TSS limit
-		 * to 0x67 as the only requirement is that the base points
-		 * outside the limit.
-		 */
-		tss->x86_tss.io_bitmap_base = IO_BITMAP_OFFSET_INVALID;
+	} else {
+		tss_invalidate_io_bitmap(tss);
 	}
 }
 
@@ -628,7 +646,8 @@ void __switch_to_xtra(struct task_struct
 
 	tifn = READ_ONCE(task_thread_info(next_p)->flags);
 	tifp = READ_ONCE(task_thread_info(prev_p)->flags);
-	switch_to_bitmap(next, tifp, tifn);
+
+	switch_to_bitmap(tifp);
 
 	propagate_user_return_notify(prev_p, next_p);
 



  parent reply index

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-13 20:42 [patch V3 00/20] x86/iopl: Prevent user space from using CLI/STI with iopl(3) Thomas Gleixner
2019-11-13 20:42 ` [patch V3 01/20] x86/ptrace: Prevent truncation of bitmap size Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 02/20] x86/process: Unify copy_thread_tls() Thomas Gleixner
2019-11-13 21:10   ` Linus Torvalds
2019-11-13 21:41     ` Thomas Gleixner
2019-11-13 22:10       ` Linus Torvalds
2019-11-13 22:33         ` Thomas Gleixner
2019-11-13 21:44     ` Brian Gerst
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 03/20] x86/cpu: Unify cpu_init() Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 04/20] x86/tss: Fix and move VMX BUILD_BUG_ON() Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 05/20] x86/iopl: Cleanup include maze Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 06/20] x86/ioperm: Simplify first ioperm() invocation logic Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 07/20] x86/ioperm: Avoid bitmap allocation if no permissions are set Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 08/20] x86/io: Speedup schedule out of I/O bitmap user Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 09/20] x86/tss: Move I/O bitmap data into a seperate struct Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 10/20] x86/ioperm: Move iobitmap data into a struct Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 11/20] x86/ioperm: Add bitmap sequence number Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` Thomas Gleixner [this message]
2019-11-13 21:19   ` [patch V3 12/20] x86/ioperm: Move TSS bitmap update to exit to user work Linus Torvalds
2019-11-13 21:21     ` Linus Torvalds
2019-11-13 21:44       ` Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 13/20] x86/ioperm: Remove bitmap if all permissions dropped Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 14/20] x86/ioperm: Share I/O bitmap if identical Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 15/20] selftests/x86/ioperm: Extend testing so the shared bitmap is exercised Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 16/20] x86/iopl: Fixup misleading comment Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 17/20] x86/iopl: Restrict iopl() permission scope Thomas Gleixner
2019-11-14 18:13   ` Borislav Petkov
2019-11-14 18:39     ` Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 18/20] x86/iopl: Remove legacy IOPL option Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:42 ` [patch V3 19/20] x86/ioperm: Extend IOPL config to control ioperm() as well Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-13 20:43 ` [patch V3 20/20] selftests/x86/iopl: Extend test to cover IOPL emulation Thomas Gleixner
2019-11-15 21:12   ` [tip: x86/iopl] " tip-bot2 for Thomas Gleixner
2019-11-14  8:43 ` [patch V3 00/20] x86/iopl: Prevent user space from using CLI/STI with iopl(3) Peter Zijlstra

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