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Linux mainline fork with MSM8998 patches | https://mainline.space | Currently supported devices: OnePlus 5/5T, Xiaomi Mi 6, F(x)tec Pro¹ (2019 QX1000 model) & Sony Xperia XZ Premium (UNTESTED!)
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Michael Ellerman 3e3786801b powerpc: Check address limit on user-mode return (TIF_FSCHECK) 
set_fs() sets the addr_limit, which is used in access_ok() to
determine if an address is a user or kernel address.

Some code paths use set_fs() to temporarily elevate the addr_limit so
that kernel code can read/write kernel memory as if it were user
memory. That is fine as long as the code can't ever return to
userspace with the addr_limit still elevated.

If that did happen, then userspace can read/write kernel memory as if
it were user memory, eg. just with write(2). In case it's not clear,
that is very bad. It has also happened in the past due to bugs.

Commit 5ea0727b16 ("x86/syscalls: Check address limit on user-mode
return") added a mechanism to check the addr_limit value before
returning to userspace. Any call to set_fs() sets a thread flag,
TIF_FSCHECK, and if we see that on the return to userspace we go out
of line to check that the addr_limit value is not elevated.

For further info see the above commit, as well as:
  https://lwn.net/Articles/722267/
  https://bugs.chromium.org/p/project-zero/issues/detail?id=990

Verified to work on 64-bit Book3S using a POC that objdumps the system
call handler, and a modified lkdtm_CORRUPT_USER_DS() that doesn't kill
the caller.

Before:
  $ sudo ./test-tif-fscheck
  ...
  0000000000000000 <.data>:
         0:       e1 f7 8a 79     rldicl. r10,r12,30,63
         4:       80 03 82 40     bne     0x384
         8:       00 40 8a 71     andi.   r10,r12,16384
         c:       78 0b 2a 7c     mr      r10,r1
        10:       10 fd 21 38     addi    r1,r1,-752
        14:       08 00 c2 41     beq-    0x1c
        18:       58 09 2d e8     ld      r1,2392(r13)
        1c:       00 00 41 f9     std     r10,0(r1)
        20:       70 01 61 f9     std     r11,368(r1)
        24:       78 01 81 f9     std     r12,376(r1)
        28:       70 00 01 f8     std     r0,112(r1)
        2c:       78 00 41 f9     std     r10,120(r1)
        30:       20 00 82 41     beq     0x50
        34:       a6 42 4c 7d     mftb    r10

After:

  $ sudo ./test-tif-fscheck
  Killed

And in dmesg:
  Invalid address limit on user-mode return
  WARNING: CPU: 1 PID: 3689 at ../include/linux/syscalls.h:260 do_notify_resume+0x140/0x170
  ...
  NIP [c00000000001ee50] do_notify_resume+0x140/0x170
  LR [c00000000001ee4c] do_notify_resume+0x13c/0x170
  Call Trace:
    do_notify_resume+0x13c/0x170 (unreliable)
    ret_from_except_lite+0x70/0x74

Performance overhead is essentially zero in the usual case, because
the bit is checked as part of the existing _TIF_USER_WORK_MASK check.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-06-03 20:43:42 +10:00
arch powerpc: Check address limit on user-mode return (TIF_FSCHECK) 2018-06-03 20:43:42 +10:00
block Revert "blk-mq: remove code for dealing with remapping queue" 2018-04-25 09:49:22 -06:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto crypto: drbg - set freed buffers to NULL 2018-04-21 00:57:00 +08:00
Documentation ocxl: Document new OCXL IOCTLs 2018-06-03 20:40:33 +10:00
drivers hvc_opal: don't set tb_ticks_per_usec in udbg_init_opal_common() 2018-06-03 20:43:34 +10:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs mm/pkeys, x86, powerpc: Display pkey in smaps if arch supports pkeys 2018-05-09 11:51:49 +10:00
include ocxl: Add an IOCTL so userspace knows what OCXL features are available 2018-06-03 20:40:32 +10:00
init Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-04-15 16:12:35 -07:00
ipc ipc/shm: fix use-after-free of shm file via remap_file_pages() 2018-04-13 17:10:27 -07:00
kernel powerpc/syscalls: switch rtas(2) to SYSCALL_DEFINE 2018-05-10 23:25:14 +10:00
lib Driver core fixes for 4.17-rc3 2018-04-27 10:12:20 -07:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
mm x86/pti: Filter at vma->vm_page_prot population 2018-04-25 11:02:51 +02:00
net A CephFS quota follow-up and fixes for two older issues in the 2018-04-27 10:56:29 -07:00
samples Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching 2018-04-20 08:51:55 -07:00
scripts powerpc/kbuild: Use flags variables rather than overriding LD/CC/AS 2018-06-01 23:08:09 +10:00
security Merge branch 'userns-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace 2018-04-24 17:58:51 -07:00
sound ALSA: dice: fix error path to destroy initialized stream data 2018-04-26 15:24:54 +02:00
tools selftests/powerpc: Add core file test for Protection Key registers 2018-05-28 18:46:36 +10:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt KVM fixes for v4.17-rc3 2018-04-27 16:13:31 -07:00
.clang-format clang-format: add configuration file 2018-04-11 10:28:35 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap Merge candidates for 4.17 merge window 2018-04-06 17:35:43 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS/CREDITS: Drop METAG ARCHITECTURE 2018-03-05 16:34:24 +00:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS MAINTAINERS: add myself as maintainer of AFFS 2018-04-28 10:30:47 -07:00
Makefile Linux v4.17-rc3 2018-04-29 14:17:42 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.