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Rik van Riel 31dc1727c1 livepatch: fix race between fork and KLP transition 
commit 747f7a2901 upstream.

The KLP transition code depends on the TIF_PATCH_PENDING and
the task->patch_state to stay in sync. On a normal (forward)
transition, TIF_PATCH_PENDING will be set on every task in
the system, while on a reverse transition (after a failed
forward one) first TIF_PATCH_PENDING will be cleared from
every task, followed by it being set on tasks that need to
be transitioned back to the original code.

However, the fork code copies over the TIF_PATCH_PENDING flag
from the parent to the child early on, in dup_task_struct and
setup_thread_stack. Much later, klp_copy_process will set
child->patch_state to match that of the parent.

However, the parent's patch_state may have been changed by KLP loading
or unloading since it was initially copied over into the child.

This results in the KLP code occasionally hitting this warning in
klp_complete_transition:

        for_each_process_thread(g, task) {
                WARN_ON_ONCE(test_tsk_thread_flag(task, TIF_PATCH_PENDING));
                task->patch_state = KLP_UNDEFINED;
        }

Set, or clear, the TIF_PATCH_PENDING flag in the child task
depending on whether or not it is needed at the time
klp_copy_process is called, at a point in copy_process where the
tasklist_lock is held exclusively, preventing races with the KLP
code.

The KLP code does have a few places where the state is changed
without the tasklist_lock held, but those should not cause
problems because klp_update_patch_state(current) cannot be
called while the current task is in the middle of fork,
klp_check_and_switch_task() which is called under the pi_lock,
which prevents rescheduling, and manipulation of the patch
state of idle tasks, which do not fork.

This should prevent this warning from triggering again in the
future, and close the race for both normal and reverse transitions.

Signed-off-by: Rik van Riel <riel@surriel.com>
Reported-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Fixes: d83a7cb375 ("livepatch: change to a per-task consistency model")
Cc: stable@kernel.org
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220808150019.03d6a67b@imladris.surriel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-10-26 12:34:30 +02:00
arch powerpc/boot: Explicitly disable usage of SPE instructions 2022-10-26 12:34:25 +02:00
block block: blk_queue_enter() / __bio_queue_enter() must return -EAGAIN for nowait 2022-09-23 14:15:48 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-22 14:22:01 +02:00
crypto KEYS: asymmetric: enforce SM2 signature use pkey algo 2022-08-17 14:24:28 +02:00
Documentation fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE 2022-10-26 12:34:27 +02:00
drivers fbdev: smscufx: Fix use-after-free in ufx_ops_open() 2022-10-26 12:34:26 +02:00
fs ext4: update 'state->fc_regions_size' after successful memory allocation 2022-10-26 12:34:30 +02:00
include fs: record I_DIRTY_TIME even if inode already has I_DIRTY_INODE 2022-10-26 12:34:27 +02:00
init stack: Declare {randomize_,}kstack_offset to fix Sparse warnings 2022-08-17 14:23:10 +02:00
ipc ipc/mqueue: use get_tree_nodev() in mqueue_get_tree() 2022-06-09 10:23:10 +02:00
kernel livepatch: fix race between fork and KLP transition 2022-10-26 12:34:30 +02:00
lib crypto: lib - remove unneeded selection of XOR_BLOCKS 2022-09-05 10:30:03 +02:00
LICENSES
mm mm/mmap: undo ->mmap() when arch_validate_flags() fails 2022-10-26 12:34:24 +02:00
net wifi: mac80211: fix MBSSID parsing use-after-free 2022-10-15 07:59:05 +02:00
samples samples/landlock: Format with clang-format 2022-06-09 10:23:23 +02:00
scripts Makefile.extrawarn: Move -Wcast-function-type-strict to W=1 2022-10-12 09:53:26 +02:00
security hardening: Remove Clang's enable flag for -ftrivial-auto-var-init=zero 2022-10-26 12:34:28 +02:00
sound ASoC: wcd934x: fix order of Slimbus unprepare/disable 2022-10-26 12:34:21 +02:00
tools perf parse-events: Identify broken modifiers 2022-10-12 09:53:28 +02:00
usr
virt KVM: SEV: add cache flush to solve SEV cache incoherency issues 2022-09-23 14:15:52 +02:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore
.mailmap
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS Input: goodix - add a goodix.h header file 2022-07-12 16:34:51 +02:00
Makefile hardening: Remove Clang's enable flag for -ftrivial-auto-var-init=zero 2022-10-26 12:34:28 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
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Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
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    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.