When the FUTEX_ROBUST_UNLOCK mechanism is used for unlocking (PI-)futexes,
then the unlock sequence in user space looks like this:
1) robust_list_set_op_pending(mutex);
2) robust_list_remove(mutex);
lval = gettid();
3) if (atomic_try_cmpxchg(&mutex->lock, lval, 0))
4) robust_list_clear_op_pending();
else
5) sys_futex(OP | FUTEX_ROBUST_UNLOCK, ....);
That still leaves a minimal race window between #3 and #4 where the mutex
could be acquired by some other task, which observes that it is the last
user and:
1) unmaps the mutex memory
2) maps a different file, which ends up covering the same address
When then the original task exits before reaching #5 then the kernel robust
list handling observes the pending op entry and tries to fix up user space.
In case that the newly mapped data contains the TID of the exiting thread
at the address of the mutex/futex the kernel will set the owner died bit in
that memory and therefore corrupt unrelated data.
On X86 this boils down to this simplified assembly sequence:
mov %esi,%eax // Load TID into EAX
xor %ecx,%ecx // Set ECX to 0
#3 lock cmpxchg %ecx,(%rdi) // Try the TID -> 0 transition
.Lstart:
jnz .Lend
#4 movq %rcx,(%rdx) // Clear list_op_pending
.Lend:
If the cmpxchg() succeeds and the task is interrupted before it can clear
list_op_pending in the robust list head (#4) and the task crashes in a
signal handler or gets killed then it ends up in do_exit() and subsequently
in the robust list handling, which then might run into the unmap/map issue
described above.
This is only relevant when user space was interrupted and a signal is
pending. The fix-up has to be done before signal delivery is attempted
because:
1) The signal might be fatal so get_signal() ends up in do_exit()
2) The signal handler might crash or the task is killed before returning
from the handler. At that point the instruction pointer in pt_regs is
not longer the instruction pointer of the initially interrupted unlock
sequence.
The right place to handle this is in __exit_to_user_mode_loop() before
invoking arch_do_signal_or_restart() as this covers obviously both
scenarios.
As this is only relevant when the task was interrupted in user space, this
is tied to RSEQ and the generic entry code as RSEQ keeps track of user
space interrupts unconditionally even if the task does not have a RSEQ
region installed. That makes the decision very lightweight:
if (current->rseq.user_irq && within(regs, csr->unlock_ip_range))
futex_fixup_robust_unlock(regs, csr);
futex_fixup_robust_unlock() then invokes a architecture specific function
to return the pending op pointer or NULL. The function evaluates the
register content to decide whether the pending ops pointer in the robust
list head needs to be cleared.
Assuming the above unlock sequence, then on x86 this decision is the
trivial evaluation of the zero flag:
return regs->eflags & X86_EFLAGS_ZF ? regs->dx : NULL;
Other architectures might need to do more complex evaluations due to LLSC,
but the approach is valid in general. The size of the pointer is determined
from the matching range struct, which covers both 32-bit and 64-bit builds
including COMPAT.
The unlock sequence is going to be placed in the VDSO so that the kernel
can keep everything synchronized, especially the register usage. The
resulting code sequence for user space is:
if (__vdso_futex_robust_list$SZ_try_unlock(lock, tid, &pending_op) != tid)
err = sys_futex($OP | FUTEX_ROBUST_UNLOCK,....);
Both the VDSO unlock and the kernel side unlock ensure that the pending_op
pointer is always cleared when the lock becomes unlocked.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@igalia.com>
Link: https://patch.msgid.link/20260602090535.773669210@kernel.org
vdso/datapage.h includes a lot of headers which are not strictly necessary.
Some of those headers include architecture-specific vDSO headers which
prevent the usage of vdso/datapage.h in kernel code on architectures
without an vDSO. This would be useful however to write generic code using
IS_ENABLED(), for example in drivers/char/random.c.
Remove the unnecessary includes.
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://patch.msgid.link/20260227-vdso-header-cleanups-v2-13-35d60acf7410@linutronix.de
Currently there are three different open-coded variants of a time
namespace aware variant of vdso_read_begin(). They make the code hard to
read and introduce an inconsistency, as only the first copy uses
unlikely().
Split the code into a shared helper function.
Move that next to the definition of the regular vdso_read_begin(), so
that any future changes can be kept in sync easily.
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260227-vdso-cleanups-v1-2-c848b4bc4850@linutronix.de
Remove the "[]" array indicators from the struct member descriptions
to avoid kernel-doc warnings.
Warning: include/vdso/datapage.h:107 struct member 'basetime' not
described in 'vdso_clock'
Warning: include/vdso/datapage.h:107 struct member 'offset' not described
in 'vdso_clock'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260228071711.2663851-1-rdunlap@infradead.org
Type punning is necessary for get/put_unaligned() but the use of a packed
struct violates strict aliasing rules, requiring -fno-strict-aliasing to be
passed to the C compiler.
Switch to using memcpy() so that -fno-strict-aliasing isn't necessary.
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20251016205126.2882625-3-irogers@google.com
For consistency with __vdso_clock_gettime64() there should also be a
64-bit variant of clock_getres(). This will allow the extension of
CONFIG_COMPAT_32BIT_TIME to the vDSO and finally the removal of 32-bit
time types from the kernel and UAPI. The generic vDSO library already
provides nearly all necessary building blocks for architectures to
provide this function. Only a prototype is missing.
Add the prototype to the generic header so architectures can start
providing this function.
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20251223-vdso-compat-time32-v1-1-97ea7a06a543@linutronix.de
Pull VDSO updates from Thomas Gleixner:
- Further consolidation of the VDSO infrastructure and the common data
store
- Simplification of the related Kconfig logic
- Improve the VDSO selftest suite
* tag 'timers-vdso-2025-09-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
selftests: vDSO: Drop vdso_test_clock_getres
selftests: vDSO: vdso_test_abi: Add tests for clock_gettime64()
selftests: vDSO: vdso_test_abi: Test CPUTIME clocks
selftests: vDSO: vdso_test_abi: Use explicit indices for name array
selftests: vDSO: vdso_test_abi: Drop clock availability tests
selftests: vDSO: vdso_test_abi: Use ksft_finished()
selftests: vDSO: vdso_test_abi: Correctly skip whole test with missing vDSO
selftests: vDSO: Fix -Wunitialized in powerpc VDSO_CALL() wrapper
vdso: Add struct __kernel_old_timeval forward declaration to gettime.h
vdso: Gate VDSO_GETRANDOM behind HAVE_GENERIC_VDSO
vdso: Drop Kconfig GENERIC_VDSO_TIME_NS
vdso: Drop Kconfig GENERIC_VDSO_DATA_STORE
vdso: Drop kconfig GENERIC_COMPAT_VDSO
vdso: Drop kconfig GENERIC_VDSO_32
riscv: vdso: Untangle Kconfig logic
time: Build generic update_vsyscall() only with generic time vDSO
vdso/gettimeofday: Remove !CONFIG_TIME_NS stubs
vdso: Move ENABLE_COMPAT_VDSO from core to arm64
ARM: VDSO: Remove cntvct_ok global variable
vdso/datastore: Gate time data behind CONFIG_GENERIC_GETTIMEOFDAY
Compiling the kernel with gcc12.3 W=2 results in shadowing warnings:
warning: declaration of '__pptr' shadows a previous local [-Wshadow]
const struct { type x; } __packed *__pptr = (typeof(__pptr))(ptr);
note: in definition of macro '__put_unaligned_t'
__pptr->x = (val);
note: in expansion of macro '__get_unaligned_t'
__put_unaligned_t(type, __get_unaligned_t(type, src), dst);
__get_unaligned_t() and __put_unaligned_t() use a local variable named
'__pptr', which can lead to variable shadowing when these macros are used in
the same scope. This results in a -Wshadow warning during compilation.
To address this issue, rename the local variables within the macros to
ensure uniqueness.
Signed-off-by: Peng Jiang <jiang.peng9@zte.com.cn>
Signed-off-by: Shao Mingyin <shao.mingyin@zte.com.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250324191230477zpGtgIRSH4mEHdtxGtgx9@zte.com.cn
To support multiple PTP clocks, the VDSO data structure needs to be
reworked. All clock specific data will end up in struct vdso_clock and in
struct vdso_time_data there will be an array of VDSO clocks.
Now that all preparatory changes are in place:
Split the clock related struct members into a separate struct
vdso_clock. Make sure all users are aware, that vdso_time_data is no longer
initialized as an array and vdso_clock is now the array inside
vdso_data. Remove the vdso_clock define, which mapped it to vdso_time_data
for the transition.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-19-c1b5c69a166f@linutronix.de
Architecture related vdso data is required in the fast path when reading
CLOCK_MONOTONIC or CLOCK_REALTIME. At the moment, this information is
located at the end of the vdso_time_data structure, which is a suboptimal
cache layout.
Move the architecture specific VDSO data right before the basetime
information, which is always required. This change does not have an impact
on architectures with CONFIG_ARCH_HAS_VDSO_DATA=n. Architectures, which
have it enabled, gain a better cache layout.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-18-c1b5c69a166f@linutronix.de
To support multiple PTP clocks, the VDSO data structure needs to be
reworked. All clock specific data will end up in struct vdso_clock and in
struct vdso_time_data there will be an array of VDSO clocks. For now,
vdso_clock is simply a define which maps vdso_clock to vdso_time_data.
Prepare all functions which need the pointer to the vdso_clock array to
work well after the structures get reworked. Replace the struct vdso_time_data
pointer with a struct vdso_clock pointer where applicable.
No functional change.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-5-c1b5c69a166f@linutronix.de
Multiple PTP clocks, which are independent of timekeeping, are required for
systems, which utilize PTP for synchronizing e.g. automation systems
independent of clock TAI.
PTP clocks are slow to access, but applications require fast access to the
relevant time similar to the regular timekeeping relevant clocks.
To prepare for that the VDSO data representation must be reworked. For
transition to the new structure of the vdso, add a define which maps
vdso_clock to vdso_data. This will be removed when all users are updated
step by step.
No functional change.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-4-c1b5c69a166f@linutronix.de
vdso_time_data is not cacheline aligned at the moment. When instantiating
an array, the start of the second array member is not cache line aligned.
This increases the number of the required cache lines which needs to be
read when handling e.g. CLOCK_MONOTONIC_RAW, because the data spawns an
extra cache line if the previous data does not end at a cache line
boundary.
Therefore make struct vdso_time_data cacheline aligned.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250303-vdso-clock-v1-3-c1b5c69a166f@linutronix.de
