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Filename Latest commit message Latest commit date
Christophe Leroy a82471a14a powerpc/mm: Fix lockup on kernel exec fault
commit cd5d5e602f502895e47e18cd46804d6d7014e65c upstream.

The powerpc kernel is not prepared to handle exec faults from kernel.
Especially, the function is_exec_fault() will return 'false' when an
exec fault is taken by kernel, because the check is based on reading
current->thread.regs->trap which contains the trap from user.

For instance, when provoking a LKDTM EXEC_USERSPACE test,
current->thread.regs->trap is set to SYSCALL trap (0xc00), and
the fault taken by the kernel is not seen as an exec fault by
set_access_flags_filter().

Commit d7df2443cd ("powerpc/mm: Fix spurious segfaults on radix
with autonuma") made it clear and handled it properly. But later on
commit d3ca587404 ("powerpc/mm: Fix reporting of kernel execute
faults") removed that handling, introducing test based on error_code.
And here is the problem, because on the 603 all upper bits of SRR1
get cleared when the TLB instruction miss handler bails out to ISI.

Until commit cbd7e6ca0210 ("powerpc/fault: Avoid heavy
search_exception_tables() verification"), an exec fault from kernel
at a userspace address was indirectly caught by the lack of entry for
that address in the exception tables. But after that commit the
kernel mainly relies on KUAP or on core mm handling to catch wrong
user accesses. Here the access is not wrong, so mm handles it.
It is a minor fault because PAGE_EXEC is not set,
set_access_flags_filter() should set PAGE_EXEC and voila.
But as is_exec_fault() returns false as explained in the beginning,
set_access_flags_filter() bails out without setting PAGE_EXEC flag,
which leads to a forever minor exec fault.

As the kernel is not prepared to handle such exec faults, the thing to
do is to fire in bad_kernel_fault() for any exec fault taken by the
kernel, as it was prior to commit d3ca587404.

Fixes: d3ca587404 ("powerpc/mm: Fix reporting of kernel execute faults")
Cc: stable@vger.kernel.org # v4.14+
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/024bb05105050f704743a0083fe3548702be5706.1625138205.git.christophe.leroy@csgroup.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-07-19 08:53:14 +02:00
arch powerpc/mm: Fix lockup on kernel exec fault 2021-07-19 08:53:14 +02:00
block blk-wbt: make sure throttle is enabled properly 2021-07-14 16:53:25 +02:00
certs certs: Move load_system_certificate_list to a common function 2021-06-30 08:47:55 -04:00
crypto crypto: shash - avoid comparing pointers to exported functions under CFI 2021-07-14 16:53:13 +02:00
Documentation clocksource: Retry clock read if long delays detected 2021-07-14 16:53:18 +02:00
drivers crypto: ccp - Annotate SEV Firmware file names 2021-07-19 08:53:14 +02:00
fs fscrypt: don't ignore minor_hash when hash is 0 2021-07-19 08:53:14 +02:00
include sctp: validate from_addr_param return 2021-07-19 08:53:13 +02:00
init kbuild: add CONFIG_LD_IS_LLD 2021-06-30 08:47:44 -04:00
ipc
kernel bpf: Fix up register-based shifts in interpreter to silence KUBSAN 2021-07-19 08:53:11 +02:00
lib lib: vsprintf: Fix handling of number field widths in vsscanf 2021-07-14 16:53:16 +02:00
LICENSES
mm mm/z3fold: fix potential memory leak in z3fold_destroy_pool() 2021-07-14 16:53:47 +02:00
net sctp: add size validation when walking chunks 2021-07-19 08:53:13 +02:00
samples samples/bpf: Fix the error return code of xdp_redirect's main() 2021-07-14 16:53:30 +02:00
scripts kbuild: Fix objtool dependency for 'OBJECT_FILES_NON_STANDARD_<obj> := n' 2021-07-14 16:53:20 +02:00
security selinux: use __GFP_NOWARN with GFP_NOWAIT in the AVC 2021-07-19 08:53:10 +02:00
sound ASoC: atmel-i2s: Fix usage of capture and playback at the same time 2021-07-14 16:53:46 +02:00
tools perf bench: Fix 2 memory sanitizer warnings 2021-07-19 08:53:14 +02:00
usr
virt KVM: do not allow mapping valid but non-reference-counted pages 2021-06-30 08:47:50 -04:00
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Makefile Linux 5.4.132 2021-07-14 16:53:49 +02:00
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.