216 lines
6.2 KiB
C
216 lines
6.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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#include <linux/compiler.h>
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#include <linux/context_tracking.h>
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#include <linux/errno.h>
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#include <linux/nospec.h>
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#include <linux/ptrace.h>
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#include <linux/randomize_kstack.h>
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#include <linux/syscalls.h>
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#include <asm/daifflags.h>
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#include <asm/debug-monitors.h>
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#include <asm/exception.h>
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#include <asm/fpsimd.h>
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#include <asm/syscall.h>
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#include <asm/thread_info.h>
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#include <asm/unistd.h>
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long compat_arm_syscall(struct pt_regs *regs, int scno);
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long sys_ni_syscall(void);
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static long do_ni_syscall(struct pt_regs *regs, int scno)
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{
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#ifdef CONFIG_COMPAT
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long ret;
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if (is_compat_task()) {
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ret = compat_arm_syscall(regs, scno);
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if (ret != -ENOSYS)
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return ret;
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}
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#endif
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return sys_ni_syscall();
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}
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static long __invoke_syscall(struct pt_regs *regs, syscall_fn_t syscall_fn)
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{
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return syscall_fn(regs);
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}
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static void invoke_syscall(struct pt_regs *regs, unsigned int scno,
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unsigned int sc_nr,
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const syscall_fn_t syscall_table[])
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{
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long ret;
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add_random_kstack_offset();
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if (scno < sc_nr) {
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syscall_fn_t syscall_fn;
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syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
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ret = __invoke_syscall(regs, syscall_fn);
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} else {
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ret = do_ni_syscall(regs, scno);
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}
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syscall_set_return_value(current, regs, 0, ret);
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/*
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* Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
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* but not enough for arm64 stack utilization comfort. To keep
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* reasonable stack head room, reduce the maximum offset to 9 bits.
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*
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* The actual entropy will be further reduced by the compiler when
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* applying stack alignment constraints: the AAPCS mandates a
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* 16-byte (i.e. 4-bit) aligned SP at function boundaries.
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*
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* The resulting 5 bits of entropy is seen in SP[8:4].
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*/
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choose_random_kstack_offset(get_random_u16() & 0x1FF);
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}
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static inline bool has_syscall_work(unsigned long flags)
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{
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return unlikely(flags & _TIF_SYSCALL_WORK);
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}
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int syscall_trace_enter(struct pt_regs *regs);
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void syscall_trace_exit(struct pt_regs *regs);
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static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr,
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const syscall_fn_t syscall_table[])
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{
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unsigned long flags = read_thread_flags();
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regs->orig_x0 = regs->regs[0];
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regs->syscallno = scno;
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/*
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* BTI note:
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* The architecture does not guarantee that SPSR.BTYPE is zero
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* on taking an SVC, so we could return to userspace with a
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* non-zero BTYPE after the syscall.
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*
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* This shouldn't matter except when userspace is explicitly
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* doing something stupid, such as setting PROT_BTI on a page
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* that lacks conforming BTI/PACIxSP instructions, falling
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* through from one executable page to another with differing
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* PROT_BTI, or messing with BTYPE via ptrace: in such cases,
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* userspace should not be surprised if a SIGILL occurs on
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* syscall return.
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*
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* So, don't touch regs->pstate & PSR_BTYPE_MASK here.
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* (Similarly for HVC and SMC elsewhere.)
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*/
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local_daif_restore(DAIF_PROCCTX);
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if (flags & _TIF_MTE_ASYNC_FAULT) {
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/*
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* Process the asynchronous tag check fault before the actual
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* syscall. do_notify_resume() will send a signal to userspace
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* before the syscall is restarted.
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*/
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syscall_set_return_value(current, regs, -ERESTARTNOINTR, 0);
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return;
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}
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if (has_syscall_work(flags)) {
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/*
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* The de-facto standard way to skip a system call using ptrace
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* is to set the system call to -1 (NO_SYSCALL) and set x0 to a
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* suitable error code for consumption by userspace. However,
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* this cannot be distinguished from a user-issued syscall(-1)
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* and so we must set x0 to -ENOSYS here in case the tracer doesn't
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* issue the skip and we fall into trace_exit with x0 preserved.
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*
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* This is slightly odd because it also means that if a tracer
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* sets the system call number to -1 but does not initialise x0,
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* then x0 will be preserved for all system calls apart from a
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* user-issued syscall(-1). However, requesting a skip and not
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* setting the return value is unlikely to do anything sensible
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* anyway.
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*/
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if (scno == NO_SYSCALL)
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syscall_set_return_value(current, regs, -ENOSYS, 0);
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scno = syscall_trace_enter(regs);
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if (scno == NO_SYSCALL)
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goto trace_exit;
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}
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invoke_syscall(regs, scno, sc_nr, syscall_table);
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/*
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* The tracing status may have changed under our feet, so we have to
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* check again. However, if we were tracing entry, then we always trace
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* exit regardless, as the old entry assembly did.
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*/
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if (!has_syscall_work(flags) && !IS_ENABLED(CONFIG_DEBUG_RSEQ)) {
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local_daif_mask();
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flags = read_thread_flags();
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if (!has_syscall_work(flags) && !(flags & _TIF_SINGLESTEP))
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return;
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local_daif_restore(DAIF_PROCCTX);
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}
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trace_exit:
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syscall_trace_exit(regs);
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}
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/*
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* As per the ABI exit SME streaming mode and clear the SVE state not
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* shared with FPSIMD on syscall entry.
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*/
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static inline void fp_user_discard(void)
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{
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/*
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* If SME is active then exit streaming mode. If ZA is active
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* then flush the SVE registers but leave userspace access to
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* both SVE and SME enabled, otherwise disable SME for the
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* task and fall through to disabling SVE too. This means
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* that after a syscall we never have any streaming mode
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* register state to track, if this changes the KVM code will
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* need updating.
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*/
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if (system_supports_sme() && test_thread_flag(TIF_SME)) {
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u64 svcr = read_sysreg_s(SYS_SVCR);
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if (svcr & SVCR_SM_MASK)
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sme_smstop_sm();
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}
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if (!system_supports_sve())
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return;
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/*
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* If SME is not active then disable SVE, the registers will
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* be cleared when userspace next attempts to access them and
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* we do not need to track the SVE register state until then.
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*/
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clear_thread_flag(TIF_SVE);
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/*
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* task_fpsimd_load() won't be called to update CPACR_EL1 in
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* ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
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* happens if a context switch or kernel_neon_begin() or context
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* modification (sigreturn, ptrace) intervenes.
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* So, ensure that CPACR_EL1 is already correct for the fast-path case.
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*/
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sve_user_disable();
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}
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void do_el0_svc(struct pt_regs *regs)
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{
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fp_user_discard();
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el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
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}
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#ifdef CONFIG_COMPAT
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void do_el0_svc_compat(struct pt_regs *regs)
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{
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el0_svc_common(regs, regs->regs[7], __NR_compat_syscalls,
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compat_sys_call_table);
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}
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#endif
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