Merge branch 'uaccess-key' into features

Heiko Carstens says:

===================
A rather large series which is supposed to fix the crash below[1], which was
seen when running the memop kernel kvm selftest.

Problem is that cmpxchg_user_key() is executing code with a non-default
key. If a system is IPL'ed with "LOAD NORMAL", and in addition the previous
system used storage keys where the fetch-protection bit is set for some pages,
and the cmpxchg_user_key() is located within such page a protection exception
will happen when executing such code.

Idea of this series is to register all code locations running with a
non-default key at compile time. All functions, which run with a non-default
key, then must explicitly call an init function which initializes the storage
key of all pages containing such code locations with default key, which
prevents such protection exceptions.

Furthermore all functions containing code which may be executed with a
non-default access key must be marked with __kprobes to prevent out-of-line
execution of any instruction of such functions, which would result in the same
problem.

By default the kernel will not issue any storage key changing instructions
like before, which will preserve the keyless-subset mode optimizations in
hosts.

Other possible implementations which I discarded:

- Moving the code to an own section. This would require an s390 specific
  change to modpost.c, which complains about section mismatches (EX_TABLE
  entries in non-default text section). No other architecture has something
  similar, so let's keep this architecture specific hack local.

- Just apply the default storage key to the whole kprobes text
  section. However this would add special s390 semantics to the kprobes text
  section, which no other architecture has. History has shown that such hacks
  fire back sooner or later.

Furthermore, and to keep this whole stuff quite simple, this only works for
code locations in core kernel code, not within modules. After this series
there is no module code left with such code, and as of now I don't see any new
kernel code which runs with a non-default access key.

Note: the original crash can be reproduced by replacing

page_set_storage_key(real, PAGE_DEFAULT_KEY, 1);

with

page_set_storage_key(real, 8, 1);

in arch/s390/kernel/skey.c:__skey_regions_initialize()

And then run tools/testing/selftests/kvm/s390/memop from the kernel selftests.

[1]:

Unable to handle kernel pointer dereference in virtual kernel address space
Failing address: 0000000000000000 TEID: 000000000000080b
Fault in home space mode while using kernel ASCE.
AS:0000000002528007 R3:00000001ffffc007 S:00000001ffffb801 P:000000000000013d
Oops: 0004 ilc:1 [#1]SMP
Modules linked in:
CPU: 3 UID: 0 PID: 791 Comm: memop Not tainted 6.16.0-rc1-00006-g3b568201d0a6-dirty #11 NONE
Hardware name: IBM 3931 A01 704 (z/VM 7.4.0)
Krnl PSW : 0794f00180000000 000003ffe0f4d91e (__cmpxchg_user_key1+0xbe/0x190)
           R:0 T:1 IO:1 EX:1 Key:9 M:1 W:0 P:0 AS:3 CC:3 PM:0 RI:0 EA:3
Krnl GPRS: 070003ffdfbf6af0 0000000000070000 0000000095b5a300 0000000000000000
           00000000f1000000 0000000000000000 0000000000000090 0000000000000000
           0000000000000040 0000000000000018 000003ff9b23d000 0000037fe0ef7bd8
           000003ffdfbf7500 00000000962e4000 0000037f00ffffff 0000037fe0ef7aa0
Krnl Code: 000003ffe0f4d912: ad03f0a0            stosm   160(%r15),3
           000003ffe0f4d916: a7780000            lhi     %r7,0
          #000003ffe0f4d91a: b20a6000            spka    0(%r6)
          >000003ffe0f4d91e: b2790100            sacf    256
           000003ffe0f4d922: a56f0080            llill   %r6,128
           000003ffe0f4d926: 5810a000            l       %r1,0(%r10)
           000003ffe0f4d92a: 141e                nr      %r1,%r14
           000003ffe0f4d92c: c0e7ffffffff        xilf    %r14,4294967295
Call Trace:
 [<000003ffe0f4d91e>] __cmpxchg_user_key1+0xbe/0x190
 [<000003ffe0189c6e>] cmpxchg_guest_abs_with_key+0x2fe/0x370
 [<000003ffe016d28e>] kvm_s390_vm_mem_op_cmpxchg+0x17e/0x350
 [<000003ffe0173284>] kvm_arch_vm_ioctl+0x354/0x6f0
 [<000003ffe015fedc>] kvm_vm_ioctl+0x2cc/0x6e0
 [<000003ffe05348ae>] vfs_ioctl+0x2e/0x70
 [<000003ffe0535e70>] __s390x_sys_ioctl+0xe0/0x100
 [<000003ffe0f40f06>] __do_syscall+0x136/0x340
 [<000003ffe0f4cb2e>] system_call+0x6e/0x90
Last Breaking-Event-Address:
 [<000003ffe0f4d896>] __cmpxchg_user_key1+0x36/0x190
===================

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

diff --cc arch/s390/include/asm/page.h
Simple merge