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* [patch V3 00/20] x86/iopl: Prevent user space from using CLI/STI with iopl(3)
@ 2019-11-13 20:42 Thomas Gleixner
  2019-11-13 20:42 ` [patch V3 01/20] x86/ptrace: Prevent truncation of bitmap size Thomas Gleixner
                   ` (20 more replies)
  0 siblings, 21 replies; 53+ messages in thread
From: Thomas Gleixner @ 2019-11-13 20:42 UTC (permalink / raw)
  To: LKML
  Cc: x86, Andy Lutomirski, Linus Torvalds, Stephen Hemminger,
	Willy Tarreau, Juergen Gross, Sean Christopherson,
	H. Peter Anvin

This is the third version of the attempt to confine the unwanted side
effects of iopl(). The first version of this series can be found here:

   https://lore.kernel.org/r/20191106193459.581614484@linutronix.de

Second version is here:

   https://lore.kernel.org/r/20191111220314.519933535@linutronix.de

The V1 cover letter also contains a longer variant of the
background. Summary:

iopl(level = 3) enables aside of access to all 65536 I/O ports also the
usage of CLI/STI in user space.

Disabling interrupts in user space can lead to system lockups and breaks
assumptions in the kernel that userspace always runs with interrupts
enabled.

iopl() is often preferred over ioperm() as it avoids the overhead of
copying the tasks I/O bitmap to the TSS bitmap on context switch. This
overhead can be avoided by providing a all zeroes bitmap in the TSS and
switching the TSS bitmap offset to this permit all IO bitmap. It's
marginally slower than iopl() which is a one time setup, but prevents the
usage of CLI/STI in user space.

The changes vs. V3:

    - Split out the restructuring of the first/subsequent ioperm()
      invocation into a seperate patch to address the inconsisteny which
      Andy detected in the patch which introduces the concept of
      invalidating the I/O bitmap base to speed up context switching.
      This change is moved in front so the subsequent changes are
      functionally correct.

    - Moved the non HW TSS data related to I/O bitmap(s) into a seperate
      data structure. Modified version of Ingos proposed patch.

    - Made struct memeber names more consistent (Ingo)

    - Dropped the bitmap union. It is not longer necessary because V2
      already dropped the finer grained copying algorithm. The sequence
      count approach should avoid most of the copying overhead when the
      number of ioperm() using processes is very low which is the normal
      case.

    - Dropped the pointer storage of the bitmap in the TSS data as it is
      not required (Peter, Andy)

    - Fixed the missing refcount setting in the bitmap duplication code
      path. (Peter, Andy)

    - Updated changelog and comment to explain the bitmap invalidation
      logic. (Andy)

    - Removed TIF_IO_BITMAP from the TIF flags which are evaluated on the
      next task for entering the slow path.

    - Folded the NULL pointer check fix

    - Simplified the config option in the legacy removal patch (Andy)

    - Extended the scope of the config option to disable ioperm() along
      with iopl() which also mokes all related storage and functions
      compile time conditional. (Andy)

The series is also available from git:

  git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/iopl

Thanks,

	tglx
---
 arch/x86/Kconfig                        |   18 ++
 arch/x86/entry/common.c                 |    4 
 arch/x86/include/asm/io_bitmap.h        |   29 ++++
 arch/x86/include/asm/paravirt.h         |    4 
 arch/x86/include/asm/paravirt_types.h   |    2 
 arch/x86/include/asm/pgtable_32_types.h |    2 
 arch/x86/include/asm/processor.h        |  113 ++++++++++-------
 arch/x86/include/asm/ptrace.h           |    6 
 arch/x86/include/asm/switch_to.h        |   10 +
 arch/x86/include/asm/thread_info.h      |   14 +-
 arch/x86/include/asm/xen/hypervisor.h   |    2 
 arch/x86/kernel/cpu/common.c            |  188 ++++++++++++----------------
 arch/x86/kernel/doublefault.c           |    2 
 arch/x86/kernel/ioport.c                |  209 +++++++++++++++++++++-----------
 arch/x86/kernel/paravirt.c              |    2 
 arch/x86/kernel/process.c               |  200 ++++++++++++++++++++++++------
 arch/x86/kernel/process_32.c            |   77 -----------
 arch/x86/kernel/process_64.c            |   86 -------------
 arch/x86/kernel/ptrace.c                |   12 +
 arch/x86/kvm/vmx/vmx.c                  |    8 -
 arch/x86/mm/cpu_entry_area.c            |    8 +
 arch/x86/xen/enlighten_pv.c             |   10 -
 tools/testing/selftests/x86/ioperm.c    |   16 ++
 tools/testing/selftests/x86/iopl.c      |  129 ++++++++++++++++++-
 24 files changed, 674 insertions(+), 477 deletions(-)


^ permalink raw reply	[flat|nested] 53+ messages in thread
* [tip: x86/iopl] x86/ioperm: Share I/O bitmap if identical
@ 2019-11-16 11:51 tip-bot2 for Thomas Gleixner
  0 siblings, 0 replies; 53+ messages in thread
From: tip-bot2 for Thomas Gleixner @ 2019-11-16 11:51 UTC (permalink / raw)
  To: linux-tip-commits
  Cc: Thomas Gleixner, Andy Lutomirski, Ingo Molnar, Borislav Petkov,
	linux-kernel

The following commit has been merged into the x86/iopl branch of tip:

Commit-ID:     4804e382c117ce213cd5c43512cf4b1d71bb2650
Gitweb:        https://git.kernel.org/tip/4804e382c117ce213cd5c43512cf4b1d71bb2650
Author:        Thomas Gleixner <tglx@linutronix.de>
AuthorDate:    Mon, 11 Nov 2019 23:03:25 +01:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sat, 16 Nov 2019 11:24:04 +01:00

x86/ioperm: Share I/O bitmap if identical

The I/O bitmap is duplicated on fork. That's wasting memory and slows down
fork. There is no point to do so. As long as the bitmap is not modified it
can be shared between threads and processes.

Add a refcount and just share it on fork. If a task modifies the bitmap
then it has to do the duplication if and only if it is shared.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Andy Lutomirski <luto@kernel.org>

---
 arch/x86/include/asm/io_bitmap.h |  5 +++-
 arch/x86/kernel/ioport.c         | 48 +++++++++++++++++++++++++------
 arch/x86/kernel/process.c        | 39 +++----------------------
 3 files changed, 50 insertions(+), 42 deletions(-)

diff --git a/arch/x86/include/asm/io_bitmap.h b/arch/x86/include/asm/io_bitmap.h
index 784a88e..b664baa 100644
--- a/arch/x86/include/asm/io_bitmap.h
+++ b/arch/x86/include/asm/io_bitmap.h
@@ -2,15 +2,20 @@
 #ifndef _ASM_X86_IOBITMAP_H
 #define _ASM_X86_IOBITMAP_H
 
+#include <linux/refcount.h>
 #include <asm/processor.h>
 
 struct io_bitmap {
 	u64		sequence;
+	refcount_t	refcnt;
 	/* The maximum number of bytes to copy so all zero bits are covered */
 	unsigned int	max;
 	unsigned long	bitmap[IO_BITMAP_LONGS];
 };
 
+struct task_struct;
+
+void io_bitmap_share(struct task_struct *tsk);
 void io_bitmap_exit(void);
 
 void tss_update_io_bitmap(void);
diff --git a/arch/x86/kernel/ioport.c b/arch/x86/kernel/ioport.c
index f9fc69a..f82ca1c 100644
--- a/arch/x86/kernel/ioport.c
+++ b/arch/x86/kernel/ioport.c
@@ -16,6 +16,17 @@
 
 static atomic64_t io_bitmap_sequence;
 
+void io_bitmap_share(struct task_struct *tsk)
+ {
+	/*
+	 * Take a refcount on current's bitmap. It can be used by
+	 * both tasks as long as none of them changes the bitmap.
+	 */
+	refcount_inc(&current->thread.io_bitmap->refcnt);
+	tsk->thread.io_bitmap = current->thread.io_bitmap;
+	set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
+}
+
 void io_bitmap_exit(void)
 {
 	struct io_bitmap *iobm = current->thread.io_bitmap;
@@ -25,7 +36,8 @@ void io_bitmap_exit(void)
 	preempt_disable();
 	tss_update_io_bitmap();
 	preempt_enable();
-	kfree(iobm);
+	if (iobm && refcount_dec_and_test(&iobm->refcnt))
+		kfree(iobm);
 }
 
 /*
@@ -58,9 +70,32 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 			return -ENOMEM;
 
 		memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap));
+		refcount_set(&iobm->refcnt, 1);
+	}
+
+	/*
+	 * If the bitmap is not shared, then nothing can take a refcount as
+	 * current can obviously not fork at the same time. If it's shared
+	 * duplicate it and drop the refcount on the original one.
+	 */
+	if (refcount_read(&iobm->refcnt) > 1) {
+		iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
+		if (!iobm)
+			return -ENOMEM;
+		refcount_set(&iobm->refcnt, 1);
+		io_bitmap_exit();
 	}
 
 	/*
+	 * Store the bitmap pointer (might be the same if the task already
+	 * head one). Must be done here so freeing the bitmap when all
+	 * permissions are dropped has the pointer set up.
+	 */
+	t->io_bitmap = iobm;
+	/* Mark it active for context switching and exit to user mode */
+	set_thread_flag(TIF_IO_BITMAP);
+
+	/*
 	 * Update the tasks bitmap. The update of the TSS bitmap happens on
 	 * exit to user mode. So this needs no protection.
 	 */
@@ -86,16 +121,11 @@ long ksys_ioperm(unsigned long from, unsigned long num, int turn_on)
 
 	iobm->max = (max_long + 1) * sizeof(unsigned long);
 
-	/* Update the sequence number to force an update in switch_to() */
-	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
-
 	/*
-	 * Store the bitmap pointer (might be the same if the task already
-	 * head one). Set the TIF flag, just in case this is the first
-	 * invocation.
+	 * Update the sequence number to force a TSS update on return to
+	 * user mode.
 	 */
-	t->io_bitmap = iobm;
-	set_thread_flag(TIF_IO_BITMAP);
+	iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
 
 	return 0;
 }
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7ba4d54..0b19c13 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -122,37 +122,13 @@ static int set_new_tls(struct task_struct *p, unsigned long tls)
 		return do_set_thread_area_64(p, ARCH_SET_FS, tls);
 }
 
-static inline int copy_io_bitmap(struct task_struct *tsk)
-{
-	struct io_bitmap *iobm = current->thread.io_bitmap;
-
-	if (likely(!test_tsk_thread_flag(current, TIF_IO_BITMAP)))
-		return 0;
-
-	tsk->thread.io_bitmap = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL);
-
-	if (!tsk->thread.io_bitmap)
-		return -ENOMEM;
-
-	set_tsk_thread_flag(tsk, TIF_IO_BITMAP);
-	return 0;
-}
-
-static inline void free_io_bitmap(struct task_struct *tsk)
-{
-	if (tsk->thread.io_bitmap) {
-		kfree(tsk->thread.io_bitmap);
-		tsk->thread.io_bitmap = NULL;
-	}
-}
-
 int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
 		    unsigned long arg, struct task_struct *p, unsigned long tls)
 {
 	struct inactive_task_frame *frame;
 	struct fork_frame *fork_frame;
 	struct pt_regs *childregs;
-	int ret;
+	int ret = 0;
 
 	childregs = task_pt_regs(p);
 	fork_frame = container_of(childregs, struct fork_frame, regs);
@@ -199,16 +175,13 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
 	task_user_gs(p) = get_user_gs(current_pt_regs());
 #endif
 
-	ret = copy_io_bitmap(p);
-	if (ret)
-		return ret;
-
 	/* Set a new TLS for the child thread? */
-	if (clone_flags & CLONE_SETTLS) {
+	if (clone_flags & CLONE_SETTLS)
 		ret = set_new_tls(p, tls);
-		if (ret)
-			free_io_bitmap(p);
-	}
+
+	if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP)))
+		io_bitmap_share(p);
+
 	return ret;
 }
 

^ permalink raw reply	[flat|nested] 53+ messages in thread

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Thread overview: 53+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
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 ` [patch V3 12/20] x86/ioperm: Move TSS bitmap update to exit to user work Thomas Gleixner
2019-11-13 21:19   ` 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
2019-11-16 11:51 [tip: x86/iopl] x86/ioperm: Share I/O bitmap if identical tip-bot2 for Thomas Gleixner

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