Pull execve fix from Kees Cook:
- Replace remaining kmap() uses with kmap_local_page() (Fabio M. De
Francesco)
* tag 'execve-v6.0-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
exec: Replace kmap{,_atomic}() with kmap_local_page()
The use of kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page().
There are two main problems with kmap(): (1) It comes with an overhead as
mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmap’s pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.
With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and are still valid.
Since the use of kmap_local_page() in exec.c is safe, it should be
preferred everywhere in exec.c.
As said, since kmap_local_page() can be also called from atomic context,
and since remove_arg_zero() doesn't (and shouldn't ever) rely on an
implicit preempt_disable(), this function can also safely replace
kmap_atomic().
Therefore, replace kmap() and kmap_atomic() with kmap_local_page() in
fs/exec.c.
Tested with xfstests on a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel
with HIGHMEM64GB enabled.
Cc: Eric W. Biederman <ebiederm@xmission.com>
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220803182856.28246-1-fmdefrancesco@gmail.com
Commit 55e8c8eb2c ("posix-cpu-timers: Store a reference to a pid not a
task") started looking up tasks by PID when deleting a CPU timer.
When a non-leader thread calls execve, it will switch PIDs with the leader
process. Then, as it calls exit_itimers, posix_cpu_timer_del cannot find
the task because the timer still points out to the old PID.
That means that armed timers won't be disarmed, that is, they won't be
removed from the timerqueue_list. exit_itimers will still release their
memory, and when that list is later processed, it leads to a
use-after-free.
Clean up the timers from the de-threaded task before freeing them. This
prevents a reported use-after-free.
Fixes: 55e8c8eb2c ("posix-cpu-timers: Store a reference to a pid not a task")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220809170751.164716-1-cascardo@canonical.com
Pull execve updates from Kees Cook:
- Allow unsharing time namespace on vfork+exec (Andrei Vagin)
- Replace usage of deprecated kmap APIs (Fabio M. De Francesco)
- Fix spelling mistake (Zhang Jiaming)
* tag 'execve-v5.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
exec: Call kmap_local_page() in copy_string_kernel()
exec: Fix a spelling mistake
selftests/timens: add a test for vfork+exit
fs/exec: allow to unshare a time namespace on vfork+exec
The use of kmap_atomic() is being deprecated in favor of kmap_local_page().
With kmap_local_page(), the mappings are per thread, CPU local and not
globally visible. Furthermore, the mappings can be acquired from any
context (including interrupts).
Therefore, replace kmap_atomic() with kmap_local_page() in
copy_string_kernel(). Instead of open-coding local mapping + memcpy(),
use memcpy_to_page(). Delete a redundant call to flush_dcache_page().
Tested with xfstests on a QEMU/ KVM x86_32 VM, 6GB RAM, booting a kernel
with HIGHMEM64GB enabled.
Suggested-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220724212523.13317-1-fmdefrancesco@gmail.com
As Chris explains, the comment above exit_itimers() is not correct,
we can race with proc_timers_seq_ops. Change exit_itimers() to clear
signal->posix_timers with ->siglock held.
Cc: <stable@vger.kernel.org>
Reported-by: chris@accessvector.net
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Right now, a new process can't be forked in another time namespace
if it shares mm with its parent. It is prohibited, because each time
namespace has its own vvar page that is mapped into a process address
space.
When a process calls exec, it gets a new mm and so it could be "legal"
to switch time namespace in that case. This was not implemented and
now if we want to do this, we need to add another clone flag to not
break backward compatibility.
We don't have any user requests to switch times on exec except the
vfork+exec combination, so there is no reason to add a new clone flag.
As for vfork+exec, this should be safe to allow switching timens with
the current clone flag. Right now, vfork (CLONE_VFORK | CLONE_VM) fails
if a child is forked into another time namespace. With this change,
vfork creates a new process in parent's timens, and the following exec
does the actual switch to the target time namespace.
Suggested-by: Florian Weimer <fweimer@redhat.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Acked-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220613060723.197407-1-avagin@gmail.com
Pull kthread updates from Eric Biederman:
"This updates init and user mode helper tasks to be ordinary user mode
tasks.
Commit 40966e316f ("kthread: Ensure struct kthread is present for
all kthreads") caused init and the user mode helper threads that call
kernel_execve to have struct kthread allocated for them. This struct
kthread going away during execve in turned made a use after free of
struct kthread possible.
Here, commit 343f4c49f2 ("kthread: Don't allocate kthread_struct for
init and umh") is enough to fix the use after free and is simple
enough to be backportable.
The rest of the changes pass struct kernel_clone_args to clean things
up and cause the code to make sense.
In making init and the user mode helpers tasks purely user mode tasks
I ran into two complications. The function task_tick_numa was
detecting tasks without an mm by testing for the presence of
PF_KTHREAD. The initramfs code in populate_initrd_image was using
flush_delayed_fput to ensuere the closing of all it's file descriptors
was complete, and flush_delayed_fput does not work in a userspace
thread.
I have looked and looked and more complications and in my code review
I have not found any, and neither has anyone else with the code
sitting in linux-next"
* tag 'kthread-cleanups-for-v5.19' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
sched: Update task_tick_numa to ignore tasks without an mm
fork: Stop allowing kthreads to call execve
fork: Explicitly set PF_KTHREAD
init: Deal with the init process being a user mode process
fork: Generalize PF_IO_WORKER handling
fork: Explicity test for idle tasks in copy_thread
fork: Pass struct kernel_clone_args into copy_thread
kthread: Don't allocate kthread_struct for init and umh
Patch series "mm/mprotect: avoid unnecessary TLB flushes", v6.
This patchset is intended to remove unnecessary TLB flushes during
mprotect() syscalls. Once this patch-set make it through, similar and
further optimizations for MADV_COLD and userfaultfd would be possible.
Basically, there are 3 optimizations in this patch-set:
1. Use TLB batching infrastructure to batch flushes across VMAs and do
better/fewer flushes. This would also be handy for later userfaultfd
enhancements.
2. Avoid unnecessary TLB flushes. This optimization is the one that
provides most of the performance benefits. Unlike previous versions,
we now only avoid flushes that would not result in spurious
page-faults.
3. Avoiding TLB flushes on change_huge_pmd() that are only needed to
prevent the A/D bits from changing.
Andrew asked for some benchmark numbers. I do not have an easy
determinate macrobenchmark in which it is easy to show benefit. I
therefore ran a microbenchmark: a loop that does the following on
anonymous memory, just as a sanity check to see that time is saved by
avoiding TLB flushes. The loop goes:
mprotect(p, PAGE_SIZE, PROT_READ)
mprotect(p, PAGE_SIZE, PROT_READ|PROT_WRITE)
*p = 0; // make the page writable
The test was run in KVM guest with 1 or 2 threads (the second thread was
busy-looping). I measured the time (cycles) of each operation:
1 thread 2 threads
mmots +patch mmots +patch
PROT_READ 3494 2725 (-22%) 8630 7788 (-10%)
PROT_READ|WRITE 3952 2724 (-31%) 9075 2865 (-68%)
[ mmots = v5.17-rc6-mmots-2022-03-06-20-38 ]
The exact numbers are really meaningless, but the benefit is clear. There
are 2 interesting results though.
(1) PROT_READ is cheaper, while one can expect it not to be affected.
This is presumably due to TLB miss that is saved
(2) Without memory access (*p = 0), the speedup of the patch is even
greater. In that scenario mprotect(PROT_READ) also avoids the TLB flush.
As a result both operations on the patched kernel take roughly ~1500
cycles (with either 1 or 2 threads), whereas on mmotm their cost is as
high as presented in the table.
This patch (of 3):
change_pXX_range() currently does not use mmu_gather, but instead
implements its own deferred TLB flushes scheme. This both complicates the
code, as developers need to be aware of different invalidation schemes,
and prevents opportunities to avoid TLB flushes or perform them in finer
granularity.
The use of mmu_gather for modified PTEs has benefits in various scenarios
even if pages are not released. For instance, if only a single page needs
to be flushed out of a range of many pages, only that page would be
flushed. If a THP page is flushed, on x86 a single TLB invlpg instruction
can be used instead of 512 instructions (or a full TLB flush, which would
Linux would actually use by default). mprotect() over multiple VMAs
requires a single flush.
Use mmu_gather in change_pXX_range(). As the pages are not released, only
record the flushed range using tlb_flush_pXX_range().
Handle THP similarly and get rid of flush_cache_range() which becomes
redundant since tlb_start_vma() calls it when needed.
Link: https://lkml.kernel.org/r/20220401180821.1986781-1-namit@vmware.com
Link: https://lkml.kernel.org/r/20220401180821.1986781-2-namit@vmware.com
Signed-off-by: Nadav Amit <namit@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Now that kernel_execve is no longer called from kernel threads stop
supporting kernel threads calling kernel_execve.
Remove the code for converting a kthread to a normal thread in execve.
Document the restriction that kthreads may not call kernel_execve by
having kernel_execve fail if called by a kthread.
Link: https://lkml.kernel.org/r/20220506141512.516114-7-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
If kthread_is_per_cpu runs concurrently with free_kthread_struct the
kthread_struct that was just freed may be read from.
This bug was introduced by commit 40966e316f ("kthread: Ensure
struct kthread is present for all kthreads"). When kthread_struct
started to be allocated for all tasks that have PF_KTHREAD set. This
in turn required the kthread_struct to be freed in kernel_execve and
violated the assumption that kthread_struct will have the same
lifetime as the task.
Looking a bit deeper this only applies to callers of kernel_execve
which is just the init process and the user mode helper processes.
These processes really don't want to be kernel threads but are for
historical reasons. Mostly that copy_thread does not know how to take
a kernel mode function to the process with for processes without
PF_KTHREAD or PF_IO_WORKER set.
Solve this by not allocating kthread_struct for the init process and
the user mode helper processes.
This is done by adding a kthread member to struct kernel_clone_args.
Setting kthread in fork_idle and kernel_thread. Adding
user_mode_thread that works like kernel_thread except it does not set
kthread. In fork only allocating the kthread_struct if .kthread is set.
I have looked at kernel/kthread.c and since commit 40966e316f
("kthread: Ensure struct kthread is present for all kthreads") there
have been no assumptions added that to_kthread or __to_kthread will
not return NULL.
There are a few callers of to_kthread or __to_kthread that assume a
non-NULL struct kthread pointer will be returned. These functions are
kthread_data(), kthread_parmme(), kthread_exit(), kthread(),
kthread_park(), kthread_unpark(), kthread_stop(). All of those functions
can reasonably expected to be called when it is know that a task is a
kthread so that assumption seems reasonable.
Cc: stable@vger.kernel.org
Fixes: 40966e316f ("kthread: Ensure struct kthread is present for all kthreads")
Reported-by: Максим Кутявин <maximkabox13@gmail.com>
Link: https://lkml.kernel.org/r/20220506141512.516114-1-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Pull ptrace cleanups from Eric Biederman:
"This set of changes removes tracehook.h, moves modification of all of
the ptrace fields inside of siglock to remove races, adds a missing
permission check to ptrace.c
The removal of tracehook.h is quite significant as it has been a major
source of confusion in recent years. Much of that confusion was around
task_work and TIF_NOTIFY_SIGNAL (which I have now decoupled making the
semantics clearer).
For people who don't know tracehook.h is a vestiage of an attempt to
implement uprobes like functionality that was never fully merged, and
was later superseeded by uprobes when uprobes was merged. For many
years now we have been removing what tracehook functionaly a little
bit at a time. To the point where anything left in tracehook.h was
some weird strange thing that was difficult to understand"
* tag 'ptrace-cleanups-for-v5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace:
ptrace: Remove duplicated include in ptrace.c
ptrace: Check PTRACE_O_SUSPEND_SECCOMP permission on PTRACE_SEIZE
ptrace: Return the signal to continue with from ptrace_stop
ptrace: Move setting/clearing ptrace_message into ptrace_stop
tracehook: Remove tracehook.h
resume_user_mode: Move to resume_user_mode.h
resume_user_mode: Remove #ifdef TIF_NOTIFY_RESUME in set_notify_resume
signal: Move set_notify_signal and clear_notify_signal into sched/signal.h
task_work: Decouple TIF_NOTIFY_SIGNAL and task_work
task_work: Call tracehook_notify_signal from get_signal on all architectures
task_work: Introduce task_work_pending
task_work: Remove unnecessary include from posix_timers.h
ptrace: Remove tracehook_signal_handler
ptrace: Remove arch_syscall_{enter,exit}_tracehook
ptrace: Create ptrace_report_syscall_{entry,exit} in ptrace.h
ptrace/arm: Rename tracehook_report_syscall report_syscall
ptrace: Move ptrace_report_syscall into ptrace.h
Pull asm-generic updates from Arnd Bergmann:
"There are three sets of updates for 5.18 in the asm-generic tree:
- The set_fs()/get_fs() infrastructure gets removed for good.
This was already gone from all major architectures, but now we can
finally remove it everywhere, which loses some particularly tricky
and error-prone code. There is a small merge conflict against a
parisc cleanup, the solution is to use their new version.
- The nds32 architecture ends its tenure in the Linux kernel.
The hardware is still used and the code is in reasonable shape, but
the mainline port is not actively maintained any more, as all
remaining users are thought to run vendor kernels that would never
be updated to a future release.
- A series from Masahiro Yamada cleans up some of the uapi header
files to pass the compile-time checks"
* tag 'asm-generic-5.18' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic: (27 commits)
nds32: Remove the architecture
uaccess: remove CONFIG_SET_FS
ia64: remove CONFIG_SET_FS support
sh: remove CONFIG_SET_FS support
sparc64: remove CONFIG_SET_FS support
lib/test_lockup: fix kernel pointer check for separate address spaces
uaccess: generalize access_ok()
uaccess: fix type mismatch warnings from access_ok()
arm64: simplify access_ok()
m68k: fix access_ok for coldfire
MIPS: use simpler access_ok()
MIPS: Handle address errors for accesses above CPU max virtual user address
uaccess: add generic __{get,put}_kernel_nofault
nios2: drop access_ok() check from __put_user()
x86: use more conventional access_ok() definition
x86: remove __range_not_ok()
sparc64: add __{get,put}_kernel_nofault()
nds32: fix access_ok() checks in get/put_user
uaccess: fix nios2 and microblaze get_user_8()
sparc64: fix building assembly files
...
Now that all of the definitions have moved out of tracehook.h into
ptrace.h, sched/signal.h, resume_user_mode.h there is nothing left in
tracehook.h so remove it.
Update the few files that were depending upon tracehook.h to bring in
definitions to use the headers they need directly.
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-13-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
There are no remaining callers of set_fs(), so CONFIG_SET_FS
can be removed globally, along with the thread_info field and
any references to it.
This turns access_ok() into a cheaper check against TASK_SIZE_MAX.
As CONFIG_SET_FS is now gone, drop all remaining references to
set_fs()/get_fs(), mm_segment_t, user_addr_max() and uaccess_kernel().
Acked-by: Sam Ravnborg <sam@ravnborg.org> # for sparc32 changes
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Tested-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com> # for arc changes
Acked-by: Stafford Horne <shorne@gmail.com> # [openrisc, asm-generic]
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Merge more updates from Andrew Morton:
"55 patches.
Subsystems affected by this patch series: percpu, procfs, sysctl,
misc, core-kernel, get_maintainer, lib, checkpatch, binfmt, nilfs2,
hfs, fat, adfs, panic, delayacct, kconfig, kcov, and ubsan"
* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (55 commits)
lib: remove redundant assignment to variable ret
ubsan: remove CONFIG_UBSAN_OBJECT_SIZE
kcov: fix generic Kconfig dependencies if ARCH_WANTS_NO_INSTR
lib/Kconfig.debug: make TEST_KMOD depend on PAGE_SIZE_LESS_THAN_256KB
btrfs: use generic Kconfig option for 256kB page size limit
arch/Kconfig: split PAGE_SIZE_LESS_THAN_256KB from PAGE_SIZE_LESS_THAN_64KB
configs: introduce debug.config for CI-like setup
delayacct: track delays from memory compact
Documentation/accounting/delay-accounting.rst: add thrashing page cache and direct compact
delayacct: cleanup flags in struct task_delay_info and functions use it
delayacct: fix incomplete disable operation when switch enable to disable
delayacct: support swapin delay accounting for swapping without blkio
panic: remove oops_id
panic: use error_report_end tracepoint on warnings
fs/adfs: remove unneeded variable make code cleaner
FAT: use io_schedule_timeout() instead of congestion_wait()
hfsplus: use struct_group_attr() for memcpy() region
nilfs2: remove redundant pointer sbufs
fs/binfmt_elf: use PT_LOAD p_align values for static PIE
const_structs.checkpatch: add frequently used ops structs
...
This helper is misleading. It tests for an ongoing exec as well as
the process having received a fatal signal.
Sometimes it is appropriate to treat an on-going exec differently than
a process that is shutting down due to a fatal signal. In particular
taking the fast path out of exit_signals instead of retargeting
signals is not appropriate during exec, and not changing the the exit
code in do_group_exit during exec.
Removing the helper makes it more obvious what is going on as both
cases must be coded for explicitly.
While removing the helper fix the two cases where I have observed
using signal_group_exit resulted in the wrong result.
In exit_signals only test for SIGNAL_GROUP_EXIT so that signals are
retargetted during an exec.
In do_group_exit use 0 as the exit code during an exec as de_thread
does not set group_exit_code. As best as I can determine
group_exit_code has been is set to 0 most of the time during
de_thread. During a thread group stop group_exit_code is set to the
stop signal and when the thread group receives SIGCONT group_exit_code
is reset to 0.
Link: https://lkml.kernel.org/r/20211213225350.27481-8-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
