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Alexey Kardashevskiy 60a707d0c9 powerpc/kuap: Restore AMR after replaying soft interrupts 
Since de78a9c42a ("powerpc: Add a framework for Kernel Userspace
Access Protection"), user access helpers call user_{read|write}_access_{begin|end}
when user space access is allowed.

Commit 890274c2dc ("powerpc/64s: Implement KUAP for Radix MMU") made
the mentioned helpers program a AMR special register to allow such
access for a short period of time, most of the time AMR is expected to
block user memory access by the kernel.

Since the code accesses the user space memory, unsafe_get_user() calls
might_fault() which calls arch_local_irq_restore() if either
CONFIG_PROVE_LOCKING or CONFIG_DEBUG_ATOMIC_SLEEP is enabled.
arch_local_irq_restore() then attempts to replay pending soft
interrupts as KUAP regions have hardware interrupts enabled.

If a pending interrupt happens to do user access (performance
interrupts do that), it enables access for a short period of time so
after returning from the replay, the user access state remains blocked
and if a user page fault happens - "Bug: Read fault blocked by AMR!"
appears and SIGSEGV is sent.

An example trace:
  Bug: Read fault blocked by AMR!
  WARNING: CPU: 0 PID: 1603 at /home/aik/p/kernel/arch/powerpc/include/asm/book3s/64/kup-radix.h:145
  CPU: 0 PID: 1603 Comm: amr Not tainted 5.10.0-rc6_v5.10-rc6_a+fstn1 #24
  NIP:  c00000000009ece8 LR: c00000000009ece4 CTR: 0000000000000000
  REGS: c00000000dc63560 TRAP: 0700   Not tainted  (5.10.0-rc6_v5.10-rc6_a+fstn1)
  MSR:  8000000000021033 <SF,ME,IR,DR,RI,LE>  CR: 28002888  XER: 20040000
  CFAR: c0000000001fa928 IRQMASK: 1
  GPR00: c00000000009ece4 c00000000dc637f0 c000000002397600 000000000000001f
  GPR04: c0000000020eb318 0000000000000000 c00000000dc63494 0000000000000027
  GPR08: c00000007fe4de68 c00000000dfe9180 0000000000000000 0000000000000001
  GPR12: 0000000000002000 c0000000030a0000 0000000000000000 0000000000000000
  GPR16: 0000000000000000 0000000000000000 0000000000000000 bfffffffffffffff
  GPR20: 0000000000000000 c0000000134a4020 c0000000019c2218 0000000000000fe0
  GPR24: 0000000000000000 0000000000000000 c00000000d106200 0000000040000000
  GPR28: 0000000000000000 0000000000000300 c00000000dc63910 c000000001946730
  NIP __do_page_fault+0xb38/0xde0
  LR  __do_page_fault+0xb34/0xde0
  Call Trace:
    __do_page_fault+0xb34/0xde0 (unreliable)
    handle_page_fault+0x10/0x2c
  --- interrupt: 300 at strncpy_from_user+0x290/0x440
      LR = strncpy_from_user+0x284/0x440
    strncpy_from_user+0x2f0/0x440 (unreliable)
    getname_flags+0x88/0x2c0
    do_sys_openat2+0x2d4/0x5f0
    do_sys_open+0xcc/0x140
    system_call_exception+0x160/0x240
    system_call_common+0xf0/0x27c

To fix it save/restore the AMR when replaying interrupts, and also
add a check if AMR was not blocked prior to replaying interrupts.

Originally found by syzkaller.

Fixes: 890274c2dc ("powerpc/64s: Implement KUAP for Radix MMU")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Use normal commit citation format and add full oops log to
      change log, move kuap_check_amr() into the restore routine to
      avoid warnings about unreconciled IRQ state]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210202091541.36499-1-aik@ozlabs.ru
2021-02-11 23:35:05 +11:00
arch powerpc/kuap: Restore AMR after replaying soft interrupts 2021-02-11 23:35:05 +11:00
block SCSI fixes on 20210101 2021-01-01 12:58:07 -08:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: aegis128 - avoid spurious references crypto_aegis128_update_simd 2020-12-04 18:16:53 +11:00
Documentation A small set of late-arriving, small documentation fixes. 2020-12-24 14:20:33 -08:00
drivers cxl: Reduce scope for the variable “mm” in cxllib_get_PE_attributes() 2021-01-31 22:35:50 +11:00
fs block-5.11-2021-01-01 2021-01-01 12:49:09 -08:00
include SCSI fixes on 20210101 2021-01-01 12:58:07 -08:00
init kasan, arm64: only use kasan_depth for software modes 2020-12-22 12:55:07 -08:00
ipc Merge branch 'akpm' (patches from Andrew) 2020-12-15 12:53:37 -08:00
kernel io_uring-5.11-2021-01-01 2021-01-01 12:29:49 -08:00
lib zlib: move EXPORT_SYMBOL() and MODULE_LICENSE() out of dfltcc_syms.c 2020-12-29 15:36:49 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm mm: slub: call account_slab_page() after slab page initialization 2020-12-29 15:36:49 -08:00
net libceph: align session_key and con_secret to 16 bytes 2020-12-28 20:34:33 +01:00
samples ARM: SoC drivers for v5.11 2020-12-16 16:38:41 -08:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-01 12:26:39 -08:00
security Provide a fix for the incorrect handling of privilege 2020-12-24 14:08:43 -08:00
sound sound fixes for 5.11-rc1 2020-12-23 15:11:08 -08:00
tools selftests/powerpc: Add VF recovery tests 2021-01-31 22:35:47 +11:00
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 ARM: 2020-12-20 10:44:05 -08:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap RDMA 5.11 pull request 2020-12-16 13:42:26 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
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 branches 'pm-cpufreq' and 'pm-cpuidle' 2021-01-02 10:16:32 +01:00
Makefile Linux 5.11-rc2 2021-01-03 15:55:30 -08:00
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.