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Diffstat (limited to 'src/charset.c')

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1 files changed, 1 insertions, 1 deletions

// SPDX-License-Identifier: GPL-2.0+ /* * Restartable sequences system call * * Copyright (C) 2015, Google, Inc., * Paul Turner <pjt@google.com> and Andrew Hunter <ahh@google.com> * Copyright (C) 2015-2018, EfficiOS Inc., * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> */ #include <linux/sched.h> #include <linux/uaccess.h> #include <linux/syscalls.h> #include <linux/rseq.h> #include <linux/types.h> #include <asm/ptrace.h> #define CREATE_TRACE_POINTS #include <trace/events/rseq.h> #define RSEQ_CS_PREEMPT_MIGRATE_FLAGS (RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE | \ RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT) /* * * Restartable sequences are a lightweight interface that allows * user-level code to be executed atomically relative to scheduler * preemption and signal delivery. Typically used for implementing * per-cpu operations. * * It allows user-space to perform update operations on per-cpu data * without requiring heavy-weight atomic operations. * * Detailed algorithm of rseq user-space assembly sequences: * * init(rseq_cs) * cpu = TLS->rseq::cpu_id_start * [1] TLS->rseq::rseq_cs = rseq_cs * [start_ip] ---------------------------- * [2] if (cpu != TLS->rseq::cpu_id) * goto abort_ip; * [3] <last_instruction_in_cs> * [post_commit_ip] ---------------------------- * * The address of jump target abort_ip must be outside the critical * region, i.e.: * * [abort_ip] < [start_ip] || [abort_ip] >= [post_commit_ip] * * Steps [2]-[3] (inclusive) need to be a sequence of instructions in * userspace that can handle being interrupted between any of those * instructions, and then resumed to the abort_ip. * * 1. Userspace stores the address of the struct rseq_cs assembly * block descriptor into the rseq_cs field of the registered * struct rseq TLS area. This update is performed through a single * store within the inline assembly instruction sequence. * [start_ip] * * 2. Userspace tests to check whether the current cpu_id field match * the cpu number loaded before start_ip, branching to abort_ip * in case of a mismatch. * * If the sequence is preempted or interrupted by a signal * at or after start_ip and before post_commit_ip, then the kernel * clears TLS->__rseq_abi::rseq_cs, and sets the user-space return * ip to abort_ip before returning to user-space, so the preempted * execution resumes at abort_ip. * * 3. Userspace critical section final instruction before * post_commit_ip is the commit. The critical section is * self-terminating. * [post_commit_ip] * * 4. <success> * * On failure at [2], or if interrupted by preempt or signal delivery * between [1] and [3]: * * [abort_ip] * F1. <failure> */ static int rseq_update_cpu_id(struct task_struct *t) { u32 cpu_id = raw_smp_processor_id(); if (put_user(cpu_id, &t->rseq->cpu_id_start)) return -EFAULT; if (put_user(cpu_id, &t->rseq->cpu_id)) return -EFAULT; trace_rseq_update(t); return 0; } static int rseq_reset_rseq_cpu_id(struct task_struct *t) { u32 cpu_id_start = 0, cpu_id = RSEQ_CPU_ID_UNINITIALIZED; /* * Reset cpu_id_start to its initial state (0). */ if (put_user(cpu_id_start, &t->rseq->cpu_id_start)) return -EFAULT; /* * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming * in after unregistration can figure out that rseq needs to be * registered again. */ if (put_user(cpu_id, &t->rseq->cpu_id)) return -EFAULT; return 0; } static int rseq_get_rseq_cs(struct task_struct *t, struct rseq_cs *rseq_cs) { struct rseq_cs __user *urseq_cs; u64 ptr; u32 __user *usig; u32 sig; int ret; if (copy_from_user(&ptr, &t->rseq->rseq_cs.ptr64, sizeof(ptr))) return -EFAULT; if (!ptr) { memset(rseq_cs, 0, sizeof(*rseq_cs)); return 0; } if (ptr >= TASK_SIZE) return -EINVAL; urseq_cs = (struct rseq_cs __user *)(unsigned long)ptr; if (copy_from_user(rseq_cs, urseq_cs, sizeof(*rseq_cs))) return -EFAULT; if (rseq_cs->start_ip >= TASK_SIZE || rseq_cs->start_ip + rseq_cs->post_commit_offset >= TASK_SIZE || rseq_cs->abort_ip >= TASK_SIZE || rseq_cs->version > 0) return -EINVAL; /* Check for overflow. */ if (rseq_cs->start_ip + rseq_cs->post_commit_offset < rseq_cs->start_ip) return -EINVAL; /* Ensure that abort_ip is not in the critical section. */ if (rseq_cs->abort_ip - rseq_cs->start_ip < rseq_cs->post_commit_offset) return -EINVAL; usig = (u32 __user *)(unsigned long)(rseq_cs->abort_ip - sizeof(u32)); ret = get_user(sig, usig); if (ret) return ret; if (current->rseq_sig != sig) { printk_ratelimited(KERN_WARNING "Possible attack attempt. Unexpected rseq signature 0x%x, expecting 0x%x (pid=%d, addr=%p).\n", sig, current->rseq_sig, current->pid, usig); return -EINVAL; } return 0; } static int rseq_need_restart(struct task_struct *t, u32 cs_flags) { u32 flags, event_mask; int ret; /* Get thread flags. */ ret = get_user(flags, &t->rseq->flags); if (ret) return ret; /* Take critical section flags into account. */ flags |= cs_flags; /* * Restart on signal can only be inhibited when restart on * preempt and restart on migrate are inhibited too. Otherwise, * a preempted signal handler could fail to restart the prior * execution context on sigreturn. */ if (unlikely((flags & RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL) && (flags & RSEQ_CS_PREEMPT_MIGRATE_FLAGS) != RSEQ_CS_PREEMPT_MIGRATE_FLAGS)) return -EINVAL; /* * Load and clear event mask atomically with respect to * scheduler preemption. */ preempt_disable(); event_mask = t->rseq_event_mask; t->rseq_event_mask = 0; preempt_enable(); return !!(event_mask & ~flags); } static int clear_rseq_cs(struct task_struct *t) { /* * The rseq_cs field is set to NULL on preemption or signal * delivery on top of rseq assembly block, as well as on top * of code outside of the rseq assembly block. This performs * a lazy clear of the rseq_cs field. * * Set rseq_cs to NULL. */ if (clear_user(&t->rseq->rseq_cs.ptr64, sizeof(t->rseq->rseq_cs.ptr64))) return -EFAULT; return 0; } /* * Unsigned comparison will be true when ip >= start_ip, and when * ip < start_ip + post_commit_offset. */ static bool in_rseq_cs(unsigned long ip, struct rseq_cs *rseq_cs) { return ip - rseq_cs->start_ip < rseq_cs->post_commit_offset; } static int rseq_ip_fixup(struct pt_regs *regs) { unsigned long ip = instruction_pointer(regs); struct task_struct *t = current; struct rseq_cs rseq_cs; int ret; ret = rseq_get_rseq_cs(t, &rseq_cs); if (ret) return ret; /* * Handle potentially not being within a critical section. * If not nested over a rseq critical section, restart is useless. * Clear the rseq_cs pointer and return. */ if (!in_rseq_cs(ip, &rseq_cs)) return clear_rseq_cs(t); ret = rseq_need_restart(t, rseq_cs.flags); if (ret <= 0) return ret; ret = clear_rseq_cs(t); if (ret) return ret; trace_rseq_ip_fixup(ip, rseq_cs.start_ip, rseq_cs.post_commit_offset, rseq_cs.abort_ip); instruction_pointer_set(regs, (unsigned long)rseq_cs.abort_ip); return 0; } /* * This resume handler must always be executed between any of: * - preemption, * - signal delivery, * and return to user-space. * * This is how we can ensure that the entire rseq critical section * will issue the commit instruction only if executed atomically with * respect to other threads scheduled on the same CPU, and with respect * to signal handlers. */ void __rseq_handle_notify_resume(struct ksignal *ksig, struct pt_regs *regs) { struct task_struct *t = current; int ret, sig; if (unlikely(t->flags & PF_EXITING)) return; if (unlikely(!access_ok(t->rseq, sizeof(*t->rseq)))) goto error; ret = rseq_ip_fixup(regs); if (unlikely(ret < 0)) goto error; if (unlikely(rseq_update_cpu_id(t))) goto error; return; error: sig = ksig ? ksig->sig : 0; force_sigsegv(sig); } #ifdef CONFIG_DEBUG_RSEQ /* * Terminate the process if a syscall is issued within a restartable * sequence. */ void rseq_syscall(struct pt_regs *regs) { unsigned long ip = instruction_pointer(regs); struct task_struct *t = current; struct rseq_cs rseq_cs; if (!t->rseq) return; if (!access_ok(t->rseq, sizeof(*t->rseq)) || rseq_get_rseq_cs(t, &rseq_cs) || in_rseq_cs(ip, &rseq_cs)) force_sig(SIGSEGV); } #endif /* * sys_rseq - setup restartable sequences for caller thread. */ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32, sig) { int ret; if (flags & RSEQ_FLAG_UNREGISTER) { if (flags & ~RSEQ_FLAG_UNREGISTER) return -EINVAL; /* Unregister rseq for current thread. */ if (current->rseq != rseq || !current->rseq) return -EINVAL; if (rseq_len != sizeof(*rseq)) return -EINVAL; if (current->rseq_sig != sig) return -EPERM; ret = rseq_reset_rseq_cpu_id(current); if (ret) return ret; current->rseq


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