linux-stable.git/Documentation, branch v3.16.83

namei: allow restricted O_CREAT of FIFOs and regular files

2020-04-28T18:03:36+00:00

commit 30aba6656f61ed44cba445a3c0d38b296fa9e8f5 upstream.

Disallows open of FIFOs or regular files not owned by the user in world
writable sticky directories, unless the owner is the same as that of the
directory or the file is opened without the O_CREAT flag.  The purpose
is to make data spoofing attacks harder.  This protection can be turned
on and off separately for FIFOs and regular files via sysctl, just like
the symlinks/hardlinks protection.  This patch is based on Openwall's
"HARDEN_FIFO" feature by Solar Designer.

This is a brief list of old vulnerabilities that could have been prevented
by this feature, some of them even allow for privilege escalation:

CVE-2000-1134
CVE-2007-3852
CVE-2008-0525
CVE-2009-0416
CVE-2011-4834
CVE-2015-1838
CVE-2015-7442
CVE-2016-7489

This list is not meant to be complete.  It's difficult to track down all
vulnerabilities of this kind because they were often reported without any
mention of this particular attack vector.  In fact, before
hardlinks/symlinks restrictions, fifos/regular files weren't the favorite
vehicle to exploit them.

[s.mesoraca16@gmail.com: fix bug reported by Dan Carpenter]
  Link: https://lkml.kernel.org/r/20180426081456.GA7060@mwanda
  Link: http://lkml.kernel.org/r/1524829819-11275-1-git-send-email-s.mesoraca16@gmail.com
[keescook@chromium.org: drop pr_warn_ratelimited() in favor of audit changes in the future]
[keescook@chromium.org: adjust commit subjet]
Link: http://lkml.kernel.org/r/20180416175918.GA13494@beast
Signed-off-by: Salvatore Mesoraca 
Signed-off-by: Kees Cook 
Suggested-by: Solar Designer 
Suggested-by: Kees Cook 
Cc: Al Viro 
Cc: Dan Carpenter 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings

USB: documentation: flags on usb-storage versus UAS

2020-02-11T20:03:42+00:00

commit 65cc8bf99349f651a0a2cee69333525fe581f306 upstream.

Document which flags work storage, UAS or both

Signed-off-by: Oliver Neukum 
Link: https://lore.kernel.org/r/20191114112758.32747-4-oneukum@suse.com
Signed-off-by: Greg Kroah-Hartman 
[bwh: Backported to 3.16: Drop change relating to ALWAYS_SYNC]
Signed-off-by: Ben Hutchings

x86/speculation: Fix incorrect MDS/TAA mitigation status

2020-02-11T20:03:41+00:00

commit 64870ed1b12e235cfca3f6c6da75b542c973ff78 upstream.

For MDS vulnerable processors with TSX support, enabling either MDS or
TAA mitigations will enable the use of VERW to flush internal processor
buffers at the right code path. IOW, they are either both mitigated
or both not. However, if the command line options are inconsistent,
the vulnerabilites sysfs files may not report the mitigation status
correctly.

For example, with only the "mds=off" option:

  vulnerabilities/mds:Vulnerable; SMT vulnerable
  vulnerabilities/tsx_async_abort:Mitigation: Clear CPU buffers; SMT vulnerable

The mds vulnerabilities file has wrong status in this case. Similarly,
the taa vulnerability file will be wrong with mds mitigation on, but
taa off.

Change taa_select_mitigation() to sync up the two mitigation status
and have them turned off if both "mds=off" and "tsx_async_abort=off"
are present.

Update documentation to emphasize the fact that both "mds=off" and
"tsx_async_abort=off" have to be specified together for processors that
are affected by both TAA and MDS to be effective.

 [ bp: Massage and add kernel-parameters.txt change too. ]

Fixes: 1b42f017415b ("x86/speculation/taa: Add mitigation for TSX Async Abort")
Signed-off-by: Waiman Long 
Signed-off-by: Borislav Petkov 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jiri Kosina 
Cc: Jonathan Corbet 
Cc: Josh Poimboeuf 
Cc: linux-doc@vger.kernel.org
Cc: Mark Gross 
Cc: Pawan Gupta 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Tim Chen 
Cc: Tony Luck 
Cc: Tyler Hicks 
Cc: x86-ml 
Link: https://lkml.kernel.org/r/20191115161445.30809-2-longman@redhat.com
[bwh: Backported to 3.16: adjust filenames]
Signed-off-by: Ben Hutchings

USB: rio500: Remove Rio 500 kernel driver

2019-12-19T15:57:59+00:00

commit 015664d15270a112c2371d812f03f7c579b35a73 upstream.

The Rio500 kernel driver has not been used by Rio500 owners since 2001
not long after the rio500 project added support for a user-space USB stack
through the very first versions of usbdevfs and then libusb.

Support for the kernel driver was removed from the upstream utilities
in 2008:
https://gitlab.freedesktop.org/hadess/rio500/commit/943f624ab721eb8281c287650fcc9e2026f6f5db

Cc: Cesar Miquel 
Signed-off-by: Bastien Nocera 
Link: https://lore.kernel.org/r/6251c17584d220472ce882a3d9c199c401a51a71.camel@hadess.net
Signed-off-by: Greg Kroah-Hartman 
[bwh: Backported to 3.16:
 - Also delete CONFIG_USB_RIO500 from arch/powerpc/configs/c2k_defconfig
 - Drop change to arch/arm/configs/pxa_defconfig
 - Adjust filename, content]
Signed-off-by: Ben Hutchings

x86/bugs: Add ITLB_MULTIHIT bug infrastructure

2019-11-15T00:56:52+00:00

commit db4d30fbb71b47e4ecb11c4efa5d8aad4b03dfae upstream.

Some processors may incur a machine check error possibly resulting in an
unrecoverable CPU lockup when an instruction fetch encounters a TLB
multi-hit in the instruction TLB. This can occur when the page size is
changed along with either the physical address or cache type. The relevant
erratum can be found here:

   https://bugzilla.kernel.org/show_bug.cgi?id=205195

There are other processors affected for which the erratum does not fully
disclose the impact.

This issue affects both bare-metal x86 page tables and EPT.

It can be mitigated by either eliminating the use of large pages or by
using careful TLB invalidations when changing the page size in the page
tables.

Just like Spectre, Meltdown, L1TF and MDS, a new bit has been allocated in
MSR_IA32_ARCH_CAPABILITIES (PSCHANGE_MC_NO) and will be set on CPUs which
are mitigated against this issue.

Signed-off-by: Vineela Tummalapalli 
Co-developed-by: Pawan Gupta 
Signed-off-by: Pawan Gupta 
Signed-off-by: Paolo Bonzini 
Signed-off-by: Thomas Gleixner 
[bwh: Backported to 3.16:
 - Use next available X86_BUG bit
 - Don't use BIT() in msr-index.h because it's a UAPI header
 - No support for X86_VENDOR_HYGON, ATOM_AIRMONT_NP
 - Adjust filename, context, indentation]
Signed-off-by: Ben Hutchings

x86/speculation/taa: Add documentation for TSX Async Abort

2019-11-15T00:56:50+00:00

commit a7a248c593e4fd7a67c50b5f5318fe42a0db335e upstream.

Add the documenation for TSX Async Abort. Include the description of
the issue, how to check the mitigation state, control the mitigation,
guidance for system administrators.

 [ bp: Add proper SPDX tags, touch ups by Josh and me. ]

Co-developed-by: Antonio Gomez Iglesias 

Signed-off-by: Pawan Gupta 
Signed-off-by: Antonio Gomez Iglesias 
Signed-off-by: Borislav Petkov 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Mark Gross 
Reviewed-by: Tony Luck 
Reviewed-by: Josh Poimboeuf 
[bwh: Backported to 4.4:
 - Drop changes to ReST index files
 - Drop "nosmt" documentation
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings

x86/tsx: Add "auto" option to the tsx= cmdline parameter

2019-11-15T00:56:50+00:00

commit 7531a3596e3272d1f6841e0d601a614555dc6b65 upstream.

Platforms which are not affected by X86_BUG_TAA may want the TSX feature
enabled. Add "auto" option to the TSX cmdline parameter. When tsx=auto
disable TSX when X86_BUG_TAA is present, otherwise enable TSX.

More details on X86_BUG_TAA can be found here:
https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html

 [ bp: Extend the arg buffer to accommodate "auto\0". ]

Signed-off-by: Pawan Gupta 
Signed-off-by: Borislav Petkov 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Tony Luck 
Reviewed-by: Josh Poimboeuf 
[bwh: Backported to 4.4: adjust filename]
Signed-off-by: Ben Hutchings

x86/cpu: Add a "tsx=" cmdline option with TSX disabled by default

2019-11-15T00:56:48+00:00

commit 95c5824f75f3ba4c9e8e5a4b1a623c95390ac266 upstream.

Add a kernel cmdline parameter "tsx" to control the Transactional
Synchronization Extensions (TSX) feature. On CPUs that support TSX
control, use "tsx=on|off" to enable or disable TSX. Not specifying this
option is equivalent to "tsx=off". This is because on certain processors
TSX may be used as a part of a speculative side channel attack.

Carve out the TSX controlling functionality into a separate compilation
unit because TSX is a CPU feature while the TSX async abort control
machinery will go to cpu/bugs.c.

 [ bp: - Massage, shorten and clear the arg buffer.
       - Clarifications of the tsx= possible options - Josh.
       - Expand on TSX_CTRL availability - Pawan. ]

Signed-off-by: Pawan Gupta 
Signed-off-by: Borislav Petkov 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Josh Poimboeuf 
[bwh: Backported to 3.16:
 - Drop __ro_after_init attribute
 - Adjust filenames, context]
Signed-off-by: Ben Hutchings

x86/speculation/mds: Improve CPU buffer clear documentation

2019-09-23T20:12:07+00:00

commit 9d8d0294e78a164d407133dea05caf4b84247d6a upstream.

On x86_64, all returns to usermode go through
prepare_exit_to_usermode(), with the sole exception of do_nmi().
This even includes machine checks -- this was added several years
ago to support MCE recovery.  Update the documentation.

Signed-off-by: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Frederic Weisbecker 
Cc: Greg Kroah-Hartman 
Cc: Jon Masters 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 04dcbdb80578 ("x86/speculation/mds: Clear CPU buffers on exit to user")
Link: http://lkml.kernel.org/r/999fa9e126ba6a48e9d214d2f18dbde5c62ac55c.1557865329.git.luto@kernel.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Ben Hutchings

x86/speculation/mds: Revert CPU buffer clear on double fault exit

2019-09-23T20:12:07+00:00

commit 88640e1dcd089879530a49a8d212d1814678dfe7 upstream.

The double fault ESPFIX path doesn't return to user mode at all --
it returns back to the kernel by simulating a #GP fault.
prepare_exit_to_usermode() will run on the way out of
general_protection before running user code.

Signed-off-by: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Frederic Weisbecker 
Cc: Greg Kroah-Hartman 
Cc: Jon Masters 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 04dcbdb80578 ("x86/speculation/mds: Clear CPU buffers on exit to user")
Link: http://lkml.kernel.org/r/ac97612445c0a44ee10374f6ea79c222fe22a5c4.1557865329.git.luto@kernel.org
Signed-off-by: Ingo Molnar 
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings