7cc16be1ae
commit 5499802b2284331788a440585869590f1bd63f7f upstream.
The conversion from __copy_from_user() to __get_user() by
commit d3ccc9781560 ("powerpc/signal: Use __get_user() to copy
sigset_t") introduced a regression in __get_user_sigset() for
powerpc/32. The bug was subsequently moved into
unsafe_get_user_sigset().
The bug is due to the copied 64 bit value being truncated to
32 bits while being assigned to dst->sig[0]
The regression was reported by users of the Xorg packages distributed in
Debian/powerpc --
"The symptoms are that the fb screen goes blank, with the backlight
remaining on and no errors logged in /var/log; wdm (or startx) run
with no effect (I tried logging in in the blind, with no effect).
And they are hard to kill, requiring 'kill -KILL ...'"
Fix the regression by copying each word of the sigset, not only the
first one.
__get_user_sigset() was tentatively optimised to copy 64 bits at once
in order to minimise KUAP unlock/lock impact, but the unsafe variant
doesn't suffer that, so it can just copy words.
Fixes: 887f3ceb51cd ("powerpc/signal32: Convert do_setcontext[_tm]() to user access block")
Cc: stable@vger.kernel.org # v5.13+
Reported-by: Finn Thain <fthain@linux-m68k.org>
Reported-and-tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/99ef38d61c0eb3f79c68942deb0c35995a93a777.1636966353.git.christophe.leroy@csgroup.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.