Re: [PATCH] futex: Change 'utime' parameter to be 'const ... *'
From: Alejandro Colomar (man-pages) <hidden>
Date: 2020-12-10 17:38:01
Also in:
linux-man, lkml
Hi Thomas & Ingo, I tested the changes. Everything's OK. Cheers, Alex $ uname -a Linux debian 5.10.0-rc7+alx3+ #4 SMP Thu Dec 10 18:05:03 CET 2020 x86_64 GNU/Linux .../linux/tools/testing/selftests/futex$ sudo ./run.sh [sudo] password for user: TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=0 owner=0 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=0 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=1 owner=0 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=1 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=0 owner=1 timeout=0ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=1 owner=0 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=1 owner=0 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=0 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=0 owner=0 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=0 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=0 owner=0 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=1 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=5000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=0 owner=1 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=500000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=1 locked=1 owner=0 timeout=2000000000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi: Test requeue functionality # Arguments: broadcast=0 locked=1 owner=0 timeout=2000000000ns ok 1 futex-requeue-pi # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi_mismatched_ops: Detect mismatched requeue_pi operations ok 1 futex-requeue-pi-mismatched-ops # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_requeue_pi_signal_restart: Test signal handling during requeue_pi # Arguments: <none> ok 1 futex-requeue-pi-signal-restart # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_wait_timeout: Block on a futex and wait for timeout # Arguments: timeout=100000ns ok 1 futex-wait-timeout # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_wait_wouldblock: Test the unexpected futex value in FUTEX_WAIT ok 1 futex-wait-wouldblock # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_wait_uninitialized_heap: Test the uninitialized futex value in FUTEX_WAIT ok 1 futex-wait-uninitialized-heap # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 TAP version 13 1..1 # futex_wait_private_mapped_file: Test the futex value of private file mappings in FUTEX_WAIT ok 1 futex-wait-private-mapped-file # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 On 11/28/20 1:39 PM, Alejandro Colomar wrote:
quoted hunk
futex(2) says that 'utime' is a pointer to 'const'. The implementation doesn't use 'const'; however, it _never_ modifies the contents of utime. - futex() either uses 'utime' as a pointer to struct or as a 'u32'. - In case it's used as a 'u32', it makes a copy of it, and of course it is not dereferenced. - In case it's used as a 'struct __kernel_timespec __user *', the pointer is not dereferenced inside the futex() definition, and it is only passed to a function: get_timespec64(), which accepts a 'const struct __kernel_timespec __user *'. context: ........ [[ FUTEX(2) Linux Programmer's Manual FUTEX(2) NAME futex - fast user-space locking SYNOPSIS #include <linux/futex.h> #include <stdint.h> #include <sys/time.h> long futex(uint32_t *uaddr, int futex_op, uint32_t val, const struct timespec *timeout, /* or: uint32_t val2 */ uint32_t *uaddr2, uint32_t val3); Note: There is no glibc wrapper for this system call; see NOTES. ]] $ sed -n '/SYSCALL_DEFINE.(futex\>/,/^}/p' linux/kernel/futex.c SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL; u32 val2 = 0; int cmd = op & FUTEX_CMD_MASK; if (utime && (cmd == FUTEX_WAIT || cmd == FUTEX_LOCK_PI || cmd == FUTEX_WAIT_BITSET || cmd == FUTEX_WAIT_REQUEUE_PI)) { if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG)))) return -EFAULT; if (get_timespec64(&ts, utime)) return -EFAULT; if (!timespec64_valid(&ts)) return -EINVAL; t = timespec64_to_ktime(ts); if (cmd == FUTEX_WAIT) t = ktime_add_safe(ktime_get(), t); else if (!(op & FUTEX_CLOCK_REALTIME)) t = timens_ktime_to_host(CLOCK_MONOTONIC, t); tp = &t; } /* * requeue parameter in 'utime' if cmd == FUTEX_*_REQUEUE_*. * number of waiters to wake in 'utime' if cmd == FUTEX_WAKE_OP. */ if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE || cmd == FUTEX_CMP_REQUEUE_PI || cmd == FUTEX_WAKE_OP) val2 = (u32) (unsigned long) utime; return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); } $ sed -n '/get_timespec64(/,/;/p' linux/include/linux/time.h int get_timespec64(struct timespec64 *ts, const struct __kernel_timespec __user *uts); ... Signed-off-by: Alejandro Colomar <redacted> --- Hello Thomas & Ingo, I'm sorry I couldn't test the change in my computers, as there is a bug since Linux 5.7 where I can't boot (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=974166). Alex kernel/futex.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)diff --git a/kernel/futex.c b/kernel/futex.c index 00259c7e288e..28577c7d2805 100644 --- a/kernel/futex.c +++ b/kernel/futex.c@@ -3792,8 +3792,8 @@ long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout, SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, - struct __kernel_timespec __user *, utime, u32 __user *, uaddr2, - u32, val3) + const struct __kernel_timespec __user *, utime, + u32 __user *, uaddr2, u32, val3) { struct timespec64 ts; ktime_t t, *tp = NULL;
-- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es