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461cab1de7
Linux 6.11 has getrandom() in vDSO. It operates on a thread-local opaque state allocated with mmap using flags specified by the vDSO. Multiple states are allocated at once, as many as fit into a page, and these are held in an array of available states to be doled out to each thread upon first use, and recycled when a thread terminates. As these states run low, more are allocated. To make this procedure async-signal-safe, a simple guard is used in the LSB of the opaque state address, falling back to the syscall if there's reentrancy contention. Also, _Fork() is handled by blocking signals on opaque state allocation (so _Fork() always sees a consistent state even if it interrupts a getrandom() call) and by iterating over the thread stack cache on reclaim_stack. Each opaque state will be in the free states list (grnd_alloc.states) or allocated to a running thread. The cancellation is handled by always using GRND_NONBLOCK flags while calling the vDSO, and falling back to the cancellable syscall if the kernel returns EAGAIN (would block). Since getrandom is not defined by POSIX and cancellation is supported as an extension, the cancellation is handled as 'may occur' instead of 'shall occur' [1], meaning that if vDSO does not block (the expected behavior) getrandom will not act as a cancellation entrypoint. It avoids a pthread_testcancel call on the fast path (different than 'shall occur' functions, like sem_wait()). It is currently enabled for x86_64, which is available in Linux 6.11, and aarch64, powerpc32, powerpc64, loongarch64, and s390x, which are available in Linux 6.12. Link: https://pubs.opengroup.org/onlinepubs/9799919799/nframe.html [1] Co-developed-by: Jason A. Donenfeld <Jason@zx2c4.com> Tested-by: Jason A. Donenfeld <Jason@zx2c4.com> # x86_64 Tested-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> # x86_64, aarch64 Tested-by: Xi Ruoyao <xry111@xry111.site> # x86_64, aarch64, loongarch64 Tested-by: Stefan Liebler <stli@linux.ibm.com> # s390x
110 lines
3.1 KiB
C
110 lines
3.1 KiB
C
/* Uncancelable versions of cancelable interfaces. Linux/NPTL version.
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Copyright (C) 2003-2024 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#ifndef NOT_CANCEL_H
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# define NOT_CANCEL_H
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#include <fcntl.h>
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#include <sysdep.h>
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#include <errno.h>
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#include <unistd.h>
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#include <sys/poll.h>
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#include <sys/syscall.h>
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#include <sys/wait.h>
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#include <time.h>
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#include <sys/random.h>
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/* Non cancellable open syscall. */
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__typeof (open) __open_nocancel;
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/* Non cancellable open syscall (LFS version). */
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__typeof (open64) __open64_nocancel;
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/* Non cancellable openat syscall. */
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__typeof (openat) __openat_nocancel;
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/* Non cacellable openat syscall (LFS version). */
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__typeof (openat64) __openat64_nocancel;
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/* Non cancellable read syscall. */
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__typeof (__read) __read_nocancel;
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/* Non cancellable pread syscall (LFS version). */
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__typeof (__pread64) __pread64_nocancel;
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/* Uncancelable write. */
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__typeof (__write) __write_nocancel;
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/* Uncancelable close. */
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__typeof (__close) __close_nocancel;
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/* Uncancelable fcntl. */
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__typeof (__fcntl) __fcntl64_nocancel;
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#if IS_IN (libc) || IS_IN (rtld)
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hidden_proto (__open_nocancel)
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hidden_proto (__open64_nocancel)
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hidden_proto (__openat_nocancel)
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hidden_proto (__openat64_nocancel)
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hidden_proto (__read_nocancel)
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hidden_proto (__pread64_nocancel)
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hidden_proto (__write_nocancel)
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hidden_proto (__close_nocancel)
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hidden_proto (__fcntl64_nocancel)
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#endif
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/* Non cancellable close syscall that does not also set errno in case of
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failure. */
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static inline void
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__close_nocancel_nostatus (int fd)
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{
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__close_nocancel (fd);
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}
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/* Non cancellable writev syscall that does not also set errno in case of
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failure. */
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static inline void
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__writev_nocancel_nostatus (int fd, const struct iovec *iov, int iovcnt)
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{
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INTERNAL_SYSCALL_CALL (writev, fd, iov, iovcnt);
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}
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static inline ssize_t
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__getrandom_nocancel_direct (void *buf, size_t buflen, unsigned int flags)
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{
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return INLINE_SYSCALL_CALL (getrandom, buf, buflen, flags);
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}
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__typeof (getrandom) __getrandom_nocancel attribute_hidden;
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/* Non cancellable getrandom syscall that does not also set errno in case of
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failure. */
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static inline ssize_t
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__getrandom_nocancel_nostatus_direct (void *buf, size_t buflen, unsigned int flags)
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{
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return INTERNAL_SYSCALL_CALL (getrandom, buf, buflen, flags);
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}
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static inline int
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__poll_infinity_nocancel (struct pollfd *fds, nfds_t nfds)
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{
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return INLINE_SYSCALL_CALL (ppoll, fds, nfds, NULL, NULL, 0);
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}
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#endif /* NOT_CANCEL_H */
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