linux.git/arch/x86/kernel/process.c, branch v5.6

x86/ioperm: Add new paravirt function update_io_bitmap()

2020-02-29T11:43:09+00:00

Commit 111e7b15cf10f6 ("x86/ioperm: Extend IOPL config to control ioperm()
as well") reworked the iopl syscall to use I/O bitmaps.

Unfortunately this broke Xen PV domains using that syscall as there is
currently no I/O bitmap support in PV domains.

Add I/O bitmap support via a new paravirt function update_io_bitmap which
Xen PV domains can use to update their I/O bitmaps via a hypercall.

Fixes: 111e7b15cf10f6 ("x86/ioperm: Extend IOPL config to control ioperm() as well")
Reported-by: Jan Beulich 
Signed-off-by: Juergen Gross 
Signed-off-by: Thomas Gleixner 
Tested-by: Jan Beulich 
Reviewed-by: Jan Beulich 
Cc:  # 5.5
Link: https://lkml.kernel.org/r/20200218154712.25490-1-jgross@suse.com

x86/process: Remove set but not used variables prev and next

2019-12-14T07:26:00+00:00

Remove two unused variables:

  arch/x86/kernel/process.c: In function ‘__switch_to_xtra’:
  arch/x86/kernel/process.c:618:31: warning: variable ‘next’ set but not used [-Wunused-but-set-variable]
    618 |  struct thread_struct *prev, *next;
        |                               ^~~~
  arch/x86/kernel/process.c:618:24: warning: variable ‘prev’ set but not used [-Wunused-but-set-variable]
    618 |  struct thread_struct *prev, *next;
        |

They are never used and so can be removed.

Signed-off-by: yu kuai 
Signed-off-by: Borislav Petkov 
Cc: Andy Lutomirski 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Thomas Gleixner 
Cc: x86-ml 
Cc: yi.zhang@huawei.com
Cc: zhengbin13@huawei.com
Link: https://lkml.kernel.org/r/20191213121253.10072-1-yukuai3@huawei.com

x86/ioperm: Save an indentation level in tss_update_io_bitmap()

2019-11-30T17:06:56+00:00

... for better readability.

No functional changes.

[ Minor edit. ]

Signed-off-by: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Signed-off-by: Ingo Molnar

x86/ioperm: Fix use of deprecated config option

2019-11-20T22:40:05+00:00

The commit

  111e7b15cf10 ("x86/ioperm: Extend IOPL config to control ioperm() as well")

replaced X86_IOPL_EMULATION with X86_IOPL_IOPERM. However it appears
that there was at least one spot missed as tss_update_io_bitmap() still
had a reference to it contained in the code.

The result of this is that it exposed a NULL pointer dereference as seen
below with a linux-next next-20191120 kernel:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] SMP PTI
  CPU: 5 PID: 1542 Comm: ovs-vswitchd Tainted: G        W 5.4.0-rc8-next-20191120 #125
  RIP: 0010:tss_update_io_bitmap+0x4e/0x180
  Code: 10 31 c0 65 48 03 1d 69 54 5d 6d 65 48 8b 04 25 40 8c 01 00 48 8b 10 \
	  f7 c2 00 00 40 00 0f 84 8c 00 00 00 4c 8b a0 c0 22 00 00 <49> 8b 04 \
	  24 48 39 43 68 74 2e 8b 53 70 41 39 54 24 0c 48 8d 7b 78
  RSP: 0018:ffffb8888a0ebf08 EFLAGS: 00010006
  RAX: ffff8a429811a680 RBX: ffff8a4c3f946000 RCX: 0000000000000011
  RDX: 0000000000400080 RSI: 0000000000400080 RDI: 0000000000000000
  RBP: ffffb8888a0ebf30 R08: 00007ffffb5d7ce0 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
  R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
  FS:  00007f68a9635c40(0000) GS:ffff8a4c3f940000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 0000000000000000 CR3: 000000103572a001 CR4: 00000000001606e0
  Call Trace:
   ? syscall_slow_exit_work+0x39/0xdb
   do_syscall_64+0x1a5/0x200
   entry_SYSCALL_64_after_hwframe+0x44/0xa9
  RIP: 0033:0x7f68a7aff797

Fixes: 111e7b15cf10 ("x86/ioperm: Extend IOPL config to control ioperm() as well")
Signed-off-by: Alexander Duyck 
Signed-off-by: Borislav Petkov 
Reviewed-by: Thomas Gleixner 
Cc: "H. Peter Anvin" 
Cc: Andy Lutomirski 
Cc: Ingo Molnar 
Cc: Rik van Riel 
Cc: x86-ml 
Link: https://lkml.kernel.org/r/20191120222426.3060.18462.stgit@localhost.localdomain

x86/ioperm: Extend IOPL config to control ioperm() as well

2019-11-16T10:24:06+00:00

If iopl() is disabled, then providing ioperm() does not make much sense.

Rename the config option and disable/enable both syscalls with it. Guard
the code with #ifdefs where appropriate.

Suggested-by: Andy Lutomirski 
Signed-off-by: Thomas Gleixner

x86/iopl: Restrict iopl() permission scope

2019-11-16T10:24:05+00:00

The access to the full I/O port range can be also provided by the TSS I/O
bitmap, but that would require to copy 8k of data on scheduling in the
task. As shown with the sched out optimization TSS.io_bitmap_base can be
used to switch the incoming task to a preallocated I/O bitmap which has all
bits zero, i.e. allows access to all I/O ports.

Implementing this allows to provide an iopl() emulation mode which restricts
the IOPL level 3 permissions to I/O port access but removes the STI/CLI
permission which is coming with the hardware IOPL mechansim.

Provide a config option to switch IOPL to emulation mode, make it the
default and while at it also provide an option to disable IOPL completely.

Signed-off-by: Thomas Gleixner 
Acked-by: Andy Lutomirski

x86/ioperm: Share I/O bitmap if identical

2019-11-16T10:24:04+00:00

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 
Acked-by: Andy Lutomirski

x86/ioperm: Remove bitmap if all permissions dropped

2019-11-16T10:24:03+00:00

If ioperm() results in a bitmap with all bits set (no permissions to any
I/O port), then handling that bitmap on context switch and exit to user
mode is pointless. Drop it.

Move the bitmap exit handling to the ioport code and reuse it for both the
thread exit path and dropping it. This allows to reuse this code for the
upcoming iopl() emulation.

Signed-off-by: Thomas Gleixner 
Acked-by: Andy Lutomirski

x86/ioperm: Move TSS bitmap update to exit to user work

2019-11-16T10:24:03+00:00

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

x86/ioperm: Add bitmap sequence number

2019-11-16T10:24:02+00:00

Add a globally unique sequence number which is incremented when ioperm() is
changing the I/O bitmap of a task. Store the new sequence number in the
io_bitmap structure and compare it with the sequence number of the I/O
bitmap which was last loaded on a CPU. Only update the bitmap if the
sequence is different.

That should further reduce the overhead of I/O bitmap scheduling when there
are only a few I/O bitmap users on the system.

The 64bit sequence counter is sufficient. A wraparound of the sequence
counter assuming an ioperm() call every nanosecond would require about 584
years of uptime.

Suggested-by: Linus Torvalds 
Signed-off-by: Thomas Gleixner