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Russell King 5242e3850b ARM: uaccess: fix DACR mismatch with nested exceptions 
[ Upstream commit 71f8af1110 ]

Tomas Paukrt reports that his SAM9X60 based system (ARM926, ARMv5TJ)
fails to fix up alignment faults, eventually resulting in a kernel
oops.

The problem occurs when using CONFIG_CPU_USE_DOMAINS with commit
e6978e4bf1 ("ARM: save and reset the address limit when entering an
exception").  This is because the address limit is set back to
TASK_SIZE on exception entry, and, although it is restored on exception
exit, the domain register is not.

Hence, this sequence can occur:

  interrupt
    pt_regs->addr_limit = addr_limit		// USER_DS
    addr_limit = USER_DS
    alignment exception
    __probe_kernel_read()
      old_fs = get_fs()				// USER_DS
      set_fs(KERNEL_DS)
        addr_limit = KERNEL_DS
        dacr.kernel = DOMAIN_MANAGER
        interrupt
          pt_regs->addr_limit = addr_limit	// KERNEL_DS
          addr_limit = USER_DS
          alignment exception
          __probe_kernel_read()
            old_fs = get_fs()			// USER_DS
            set_fs(KERNEL_DS)
              addr_limit = KERNEL_DS
              dacr.kernel = DOMAIN_MANAGER
            ...
            set_fs(old_fs)
              addr_limit = USER_DS
              dacr.kernel = DOMAIN_CLIENT
          ...
          addr_limit = pt_regs->addr_limit	// KERNEL_DS
        interrupt returns

At this point, addr_limit is correctly restored to KERNEL_DS for
__probe_kernel_read() to continue execution, but dacr.kernel is not,
it has been reset by the set_fs(old_fs) to DOMAIN_CLIENT.

This would not have happened prior to the mentioned commit, because
addr_limit would remain KERNEL_DS, so get_fs() would have returned
KERNEL_DS, and so would correctly nest.

This commit fixes the problem by also saving the DACR on exception
entry if either CONFIG_CPU_SW_DOMAIN_PAN or CONFIG_CPU_USE_DOMAINS are
enabled, and resetting the DACR appropriately on exception entry to
match addr_limit and PAN settings.

Fixes: e6978e4bf1 ("ARM: save and reset the address limit when entering an exception")
Reported-by: Tomas Paukrt <tomas.paukrt@advantech.cz>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2020-06-03 08:21:18 +02:00
Documentation USB: hub: Revert commit bd0e6c9614 ("usb: hub: try old enumeration scheme first for high speed devices") 2020-04-29 16:33:14 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch ARM: uaccess: fix DACR mismatch with nested exceptions 2020-06-03 08:21:18 +02:00
block iocost: protect iocg->abs_vdebt with iocg->waitq.lock 2020-05-14 07:58:27 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto gcc-10: avoid shadowing standard library 'free()' in crypto 2020-05-20 08:20:29 +02:00
drivers Input: synaptics-rmi4 - fix error return code in rmi_driver_probe() 2020-06-03 08:21:17 +02:00
fs cifs: Fix null pointer check in cifs_read 2020-06-03 08:21:14 +02:00
include net/tls: fix race condition causing kernel panic 2020-06-03 08:21:01 +02:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel sched/fair: Fix enqueue_task_fair() warning some more 2020-05-27 17:46:52 +02:00
lib vsprintf: don't obfuscate NULL and error pointers 2020-05-27 17:46:43 +02:00
mm kasan: disable branch tracing for core runtime 2020-05-27 17:46:48 +02:00
net net/tls: free record only on encryption error 2020-06-03 08:21:06 +02:00
samples samples: bpf: Fix build error 2020-06-03 08:21:15 +02:00
scripts kbuild: Remove debug info from kallsyms linking 2020-05-27 17:46:44 +02:00
security apparmor: Fix aa_label refcnt leak in policy_update 2020-05-27 17:46:42 +02:00
sound ALSA: usb-audio: add mapping for ASRock TRX40 Creator 2020-06-03 08:21:09 +02:00
tools KVM: selftests: Fix build for evmcs.h 2020-05-27 17:46:36 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm: vgic: Synchronize the whole guest on GIC{D,R}_I{S,C}ACTIVER read 2020-05-20 08:20:04 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.43 2020-05-27 17:46:53 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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.

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.