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Alexey Kardashevskiy 97ab82462a powerpc/uaccess: Avoid might_fault() when user access is enabled 
[ Upstream commit 7d506ca97b ]

The amount of code executed with enabled user space access (unlocked
KUAP) should be minimal. However with CONFIG_PROVE_LOCKING or
CONFIG_DEBUG_ATOMIC_SLEEP enabled, might_fault() calls into various
parts of the kernel, and may even end up replaying interrupts which in
turn may access user space and forget to restore the KUAP state.

The problem places are:
  1. strncpy_from_user (and similar) which unlock KUAP and call
     unsafe_get_user -> __get_user_allowed -> __get_user_nocheck()
     with do_allow=false to skip KUAP as the caller took care of it.
  2. __unsafe_put_user_goto() which is called with unlocked KUAP.

eg:
  WARNING: CPU: 30 PID: 1 at arch/powerpc/include/asm/book3s/64/kup.h:324 arch_local_irq_restore+0x160/0x190
  NIP arch_local_irq_restore+0x160/0x190
  LR  lock_is_held_type+0x140/0x200
  Call Trace:
    0xc00000007f392ff8 (unreliable)
    ___might_sleep+0x180/0x320
    __might_fault+0x50/0xe0
    filldir64+0x2d0/0x5d0
    call_filldir+0xc8/0x180
    ext4_readdir+0x948/0xb40
    iterate_dir+0x1ec/0x240
    sys_getdents64+0x80/0x290
    system_call_exception+0x160/0x280
    system_call_common+0xf0/0x27c

Change __get_user_nocheck() to look at `do_allow` to decide whether to
skip might_fault(). Since strncpy_from_user/etc call might_fault()
anyway before unlocking KUAP, there should be no visible change.

Drop might_fault() in __unsafe_put_user_goto() as it is only called
from unsafe_put_user(), which already has KUAP unlocked.

Since keeping might_fault() is still desirable for debugging, add
calls to it in user_[read|write]_access_begin(). That also allows us
to drop the is_kernel_addr() test, because there should be no code
using user_[read|write]_access_begin() in order to access a kernel
address.

Fixes: de78a9c42a ("powerpc: Add a framework for Kernel Userspace Access Protection")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[mpe: Combine with related patch from myself, merge change logs]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210204121612.32721-1-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-03-04 11:38:06 +01:00
arch powerpc/uaccess: Avoid might_fault() when user access is enabled 2021-03-04 11:38:06 +01:00
block bsg: free the request before return error code 2021-03-04 11:37:42 +01:00
certs certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
crypto crypto: ecdh_helper - Ensure 'len >= secret.len' in decode_key() 2021-03-04 11:37:49 +01:00
Documentation watch_queue: Drop references to /dev/watch_queue 2021-03-04 11:37:59 +01:00
drivers spi: pxa2xx: Fix the controller numbering for Wildcat Point 2021-03-04 11:38:06 +01:00
fs isofs: release buffer head before return 2021-03-04 11:38:00 +01:00
include iommu: Switch gather->end to the inclusive end 2021-03-04 11:38:01 +01:00
init fgraph: Initialize tracing_graph_pause at task creation 2021-02-10 09:29:16 +01:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel tracepoint: Do not fail unregistering a probe due to memory failure 2021-03-04 11:38:03 +01:00
lib udp: fix skb_copy_and_csum_datagram with odd segment sizes 2021-02-17 11:02:28 +01:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm: provide a saner PTE walking API for modules 2021-02-26 10:13:01 +01:00
net tty: convert tty_ldisc_ops 'read()' function to take a kernel pointer 2021-03-04 11:37:36 +01:00
samples watch_queue: Drop references to /dev/watch_queue 2021-03-04 11:37:59 +01:00
scripts scripts/recordmcount.pl: support big endian for ARCH sh 2021-02-26 10:13:02 +01:00
security certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
sound ASoC: simple-card-utils: Fix device module clock 2021-03-04 11:37:51 +01:00
tools kselftests: dmabuf-heaps: Fix Makefile's inclusion of the kernel's usr/include dir 2021-03-04 11:38:05 +01:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() 2021-02-26 10:13:01 +01:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-10 15:30:13 -08:00
Makefile Linux 5.10.19 2021-02-26 10:14:35 +01:00
README

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.