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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
94 lines
3.2 KiB
C
94 lines
3.2 KiB
C
/* Data for vDSO support. Linux version.
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Copyright (C) 2020-2024 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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/* This file is included in three different modes for both static (libc.a)
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and shared (rtld) modes:
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1. PROCINFO_DECL is defined, meaning we are only interested in
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declarations. For static it requires use the extern keyword along with
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the attribute_relro while for shared it will be embedded in the
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rtld_global_ro.
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2. PROCINFO_DECL and SHARED are not defined. Nothing to do, the default
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zero initializion is suffice.
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3. PROCINFO_DECL is not defined while SHARED is. Similar to 2., the zero
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initialization of rtld_global_ro is suffice. */
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#ifndef PROCINFO_CLASS
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# define PROCINFO_CLASS
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#endif
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#ifndef SHARED
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# define RELRO attribute_relro
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#else
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# define RELRO
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#endif
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#if defined PROCINFO_DECL || !defined SHARED
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# ifdef HAVE_CLOCK_GETTIME_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_clock_gettime) (clockid_t,
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struct timespec *) RELRO;
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#endif
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# ifdef HAVE_CLOCK_GETTIME64_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_clock_gettime64) (clockid_t,
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struct __timespec64 *) RELRO;
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#endif
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# ifdef HAVE_GETTIMEOFDAY_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_gettimeofday) (struct timeval *, void *) RELRO;
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#endif
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# ifdef HAVE_TIME_VSYSCALL
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PROCINFO_CLASS time_t (*_dl_vdso_time) (time_t *) RELRO;
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# endif
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# ifdef HAVE_GETCPU_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_getcpu) (unsigned *, unsigned *, void *) RELRO;
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# endif
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# ifdef HAVE_CLOCK_GETRES_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_clock_getres) (clockid_t,
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struct timespec *) RELRO;
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# endif
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# ifdef HAVE_CLOCK_GETRES64_VSYSCALL
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PROCINFO_CLASS int (*_dl_vdso_clock_getres_time64) (clockid_t,
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struct __timespec64 *) RELRO;
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# endif
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# ifdef HAVE_GETRANDOM_VSYSCALL
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PROCINFO_CLASS ssize_t (*_dl_vdso_getrandom) (void *buffer, size_t len,
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unsigned int flags, void *state,
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size_t state_len) RELRO;
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# endif
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/* PowerPC specific ones. */
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# ifdef HAVE_GET_TBFREQ
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PROCINFO_CLASS uint64_t (*_dl_vdso_get_tbfreq)(void) RELRO;
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# endif
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/* RISC-V specific ones. */
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# ifdef HAVE_RISCV_HWPROBE
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PROCINFO_CLASS int (*_dl_vdso_riscv_hwprobe)(void *,
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size_t,
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size_t,
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unsigned long *,
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unsigned int) RELRO;
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# endif
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#endif
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#undef RELRO
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#undef PROCINFO_DECL
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#undef PROCINFO_CLASS
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