// SPDX-License-Identifier: GPL-2.0-only /* * Copyright (C) 2020 ARM Ltd. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include static DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred); #ifdef CONFIG_KASAN_HW_TAGS /* Whether the MTE asynchronous mode is enabled. */ DEFINE_STATIC_KEY_FALSE(mte_async_mode); EXPORT_SYMBOL_GPL(mte_async_mode); #endif static void mte_sync_page_tags(struct page *page, pte_t old_pte, bool check_swap, bool pte_is_tagged) { if (check_swap && is_swap_pte(old_pte)) { swp_entry_t entry = pte_to_swp_entry(old_pte); if (!non_swap_entry(entry) && mte_restore_tags(entry, page)) return; } if (!pte_is_tagged) return; page_kasan_tag_reset(page); /* * We need smp_wmb() in between setting the flags and clearing the * tags because if another thread reads page->flags and builds a * tagged address out of it, there is an actual dependency to the * memory access, but on the current thread we do not guarantee that * the new page->flags are visible before the tags were updated. */ smp_wmb(); /* * Test PG_mte_tagged again in case it was racing with another * set_pte_at(). */ if (!test_and_set_bit(PG_mte_tagged, &page->flags)) mte_clear_page_tags(page_address(page)); } void mte_sync_tags(pte_t old_pte, pte_t pte) { struct page *page = pte_page(pte); long i, nr_pages = compound_nr(page); bool check_swap = nr_pages == 1; bool pte_is_tagged = pte_tagged(pte); /* Early out if there's nothing to do */ if (!check_swap && !pte_is_tagged) return; /* if PG_mte_tagged is set, tags have already been initialised */ for (i = 0; i < nr_pages; i++, page++) { if (!test_bit(PG_mte_tagged, &page->flags)) mte_sync_page_tags(page, old_pte, check_swap, pte_is_tagged); } /* ensure the tags are visible before the PTE is set */ smp_wmb(); } int memcmp_pages(struct page *page1, struct page *page2) { char *addr1, *addr2; int ret; addr1 = page_address(page1); addr2 = page_address(page2); ret = memcmp(addr1, addr2, PAGE_SIZE); if (!system_supports_mte() || ret) return ret; /* * If the page content is identical but at least one of the pages is * tagged, return non-zero to avoid KSM merging. If only one of the * pages is tagged, set_pte_at() may zero or change the tags of the * other page via mte_sync_tags(). */ if (test_bit(PG_mte_tagged, &page1->flags) || test_bit(PG_mte_tagged, &page2->flags)) return addr1 != addr2; return ret; } static inline void __mte_enable_kernel(const char *mode, unsigned long tcf) { /* Enable MTE Sync Mode for EL1. */ sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf); isb(); pr_info_once("MTE: enabled in %s mode at EL1\n", mode); } #ifdef CONFIG_KASAN_HW_TAGS void mte_enable_kernel_sync(void) { /* * Make sure we enter this function when no PE has set * async mode previously. */ WARN_ONCE(system_uses_mte_async_mode(), "MTE async mode enabled system wide!"); __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC); } void mte_enable_kernel_async(void) { __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC); /* * MTE async mode is set system wide by the first PE that * executes this function. * * Note: If in future KASAN acquires a runtime switching * mode in between sync and async, this strategy needs * to be reviewed. */ if (!system_uses_mte_async_mode()) static_branch_enable(&mte_async_mode); } #endif #ifdef CONFIG_KASAN_HW_TAGS void mte_check_tfsr_el1(void) { u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1); if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) { /* * Note: isb() is not required after this direct write * because there is no indirect read subsequent to it * (per ARM DDI 0487F.c table D13-1). */ write_sysreg_s(0, SYS_TFSR_EL1); kasan_report_async(); } } #endif static void mte_update_sctlr_user(struct task_struct *task) { /* * This must be called with preemption disabled and can only be called * on the current or next task since the CPU must match where the thread * is going to run. The caller is responsible for calling * update_sctlr_el1() later in the same preemption disabled block. */ unsigned long sctlr = task->thread.sctlr_user; unsigned long mte_ctrl = task->thread.mte_ctrl; unsigned long pref, resolved_mte_tcf; pref = __this_cpu_read(mte_tcf_preferred); resolved_mte_tcf = (mte_ctrl & pref) ? pref : mte_ctrl; sctlr &= ~SCTLR_EL1_TCF0_MASK; if (resolved_mte_tcf & MTE_CTRL_TCF_ASYNC) sctlr |= SCTLR_EL1_TCF0_ASYNC; else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC) sctlr |= SCTLR_EL1_TCF0_SYNC; task->thread.sctlr_user = sctlr; } void mte_thread_init_user(void) { if (!system_supports_mte()) return; /* clear any pending asynchronous tag fault */ dsb(ish); write_sysreg_s(0, SYS_TFSRE0_EL1); clear_thread_flag(TIF_MTE_ASYNC_FAULT); /* disable tag checking and reset tag generation mask */ set_mte_ctrl(current, 0); } void mte_thread_switch(struct task_struct *next) { if (!system_supports_mte()) return; mte_update_sctlr_user(next); /* * Check if an async tag exception occurred at EL1. * * Note: On the context switch path we rely on the dsb() present * in __switch_to() to guarantee that the indirect writes to TFSR_EL1 * are synchronized before this point. */ isb(); mte_check_tfsr_el1(); } void mte_cpu_setup(void) { u64 rgsr; /* * CnP must be enabled only after the MAIR_EL1 register has been set * up. Inconsistent MAIR_EL1 between CPUs sharing the same TLB may * lead to the wrong memory type being used for a brief window during * CPU power-up. * * CnP is not a boot feature so MTE gets enabled before CnP, but let's * make sure that is the case. */ BUG_ON(read_sysreg(ttbr0_el1) & TTBR_CNP_BIT); BUG_ON(read_sysreg(ttbr1_el1) & TTBR_CNP_BIT); /* Normal Tagged memory type at the corresponding MAIR index */ sysreg_clear_set(mair_el1, MAIR_ATTRIDX(MAIR_ATTR_MASK, MT_NORMAL_TAGGED), MAIR_ATTRIDX(MAIR_ATTR_NORMAL_TAGGED, MT_NORMAL_TAGGED)); write_sysreg_s(KERNEL_GCR_EL1, SYS_GCR_EL1); /* * If GCR_EL1.RRND=1 is implemented the same way as RRND=0, then * RGSR_EL1.SEED must be non-zero for IRG to produce * pseudorandom numbers. As RGSR_EL1 is UNKNOWN out of reset, we * must initialize it. */ rgsr = (read_sysreg(CNTVCT_EL0) & SYS_RGSR_EL1_SEED_MASK) << SYS_RGSR_EL1_SEED_SHIFT; if (rgsr == 0) rgsr = 1 << SYS_RGSR_EL1_SEED_SHIFT; write_sysreg_s(rgsr, SYS_RGSR_EL1); /* clear any pending tag check faults in TFSR*_EL1 */ write_sysreg_s(0, SYS_TFSR_EL1); write_sysreg_s(0, SYS_TFSRE0_EL1); local_flush_tlb_all(); } void mte_suspend_enter(void) { if (!system_supports_mte()) return; /* * The barriers are required to guarantee that the indirect writes * to TFSR_EL1 are synchronized before we report the state. */ dsb(nsh); isb(); /* Report SYS_TFSR_EL1 before suspend entry */ mte_check_tfsr_el1(); } void mte_suspend_exit(void) { if (!system_supports_mte()) return; mte_cpu_setup(); } long set_mte_ctrl(struct task_struct *task, unsigned long arg) { u64 mte_ctrl = (~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) & SYS_GCR_EL1_EXCL_MASK) << MTE_CTRL_GCR_USER_EXCL_SHIFT; if (!system_supports_mte()) return 0; if (arg & PR_MTE_TCF_ASYNC) mte_ctrl |= MTE_CTRL_TCF_ASYNC; if (arg & PR_MTE_TCF_SYNC) mte_ctrl |= MTE_CTRL_TCF_SYNC; task->thread.mte_ctrl = mte_ctrl; if (task == current) { preempt_disable(); mte_update_sctlr_user(task); update_sctlr_el1(task->thread.sctlr_user); preempt_enable(); } return 0; } long get_mte_ctrl(struct task_struct *task) { unsigned long ret; u64 mte_ctrl = task->thread.mte_ctrl; u64 incl = (~mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) & SYS_GCR_EL1_EXCL_MASK; if (!system_supports_mte()) return 0; ret = incl << PR_MTE_TAG_SHIFT; if (mte_ctrl & MTE_CTRL_TCF_ASYNC) ret |= PR_MTE_TCF_ASYNC; if (mte_ctrl & MTE_CTRL_TCF_SYNC) ret |= PR_MTE_TCF_SYNC; return ret; } /* * Access MTE tags in another process' address space as given in mm. Update * the number of tags copied. Return 0 if any tags copied, error otherwise. * Inspired by __access_remote_vm(). */ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, struct iovec *kiov, unsigned int gup_flags) { struct vm_area_struct *vma; void __user *buf = kiov->iov_base; size_t len = kiov->iov_len; int ret; int write = gup_flags & FOLL_WRITE; if (!access_ok(buf, len)) return -EFAULT; if (mmap_read_lock_killable(mm)) return -EIO; while (len) { unsigned long tags, offset; void *maddr; struct page *page = NULL; ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page, &vma, NULL); if (ret <= 0) break; /* * Only copy tags if the page has been mapped as PROT_MTE * (PG_mte_tagged set). Otherwise the tags are not valid and * not accessible to user. Moreover, an mprotect(PROT_MTE) * would cause the existing tags to be cleared if the page * was never mapped with PROT_MTE. */ if (!(vma->vm_flags & VM_MTE)) { ret = -EOPNOTSUPP; put_page(page); break; } WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); /* limit access to the end of the page */ offset = offset_in_page(addr); tags = min(len, (PAGE_SIZE - offset) / MTE_GRANULE_SIZE); maddr = page_address(page); if (write) { tags = mte_copy_tags_from_user(maddr + offset, buf, tags); set_page_dirty_lock(page); } else { tags = mte_copy_tags_to_user(buf, maddr + offset, tags); } put_page(page); /* error accessing the tracer's buffer */ if (!tags) break; len -= tags; buf += tags; addr += tags * MTE_GRANULE_SIZE; } mmap_read_unlock(mm); /* return an error if no tags copied */ kiov->iov_len = buf - kiov->iov_base; if (!kiov->iov_len) { /* check for error accessing the tracee's address space */ if (ret <= 0) return -EIO; else return -EFAULT; } return 0; } /* * Copy MTE tags in another process' address space at 'addr' to/from tracer's * iovec buffer. Return 0 on success. Inspired by ptrace_access_vm(). */ static int access_remote_tags(struct task_struct *tsk, unsigned long addr, struct iovec *kiov, unsigned int gup_flags) { struct mm_struct *mm; int ret; mm = get_task_mm(tsk); if (!mm) return -EPERM; if (!tsk->ptrace || (current != tsk->parent) || ((get_dumpable(mm) != SUID_DUMP_USER) && !ptracer_capable(tsk, mm->user_ns))) { mmput(mm); return -EPERM; } ret = __access_remote_tags(mm, addr, kiov, gup_flags); mmput(mm); return ret; } int mte_ptrace_copy_tags(struct task_struct *child, long request, unsigned long addr, unsigned long data) { int ret; struct iovec kiov; struct iovec __user *uiov = (void __user *)data; unsigned int gup_flags = FOLL_FORCE; if (!system_supports_mte()) return -EIO; if (get_user(kiov.iov_base, &uiov->iov_base) || get_user(kiov.iov_len, &uiov->iov_len)) return -EFAULT; if (request == PTRACE_POKEMTETAGS) gup_flags |= FOLL_WRITE; /* align addr to the MTE tag granule */ addr &= MTE_GRANULE_MASK; ret = access_remote_tags(child, addr, &kiov, gup_flags); if (!ret) ret = put_user(kiov.iov_len, &uiov->iov_len); return ret; } static ssize_t mte_tcf_preferred_show(struct device *dev, struct device_attribute *attr, char *buf) { switch (per_cpu(mte_tcf_preferred, dev->id)) { case MTE_CTRL_TCF_ASYNC: return sysfs_emit(buf, "async\n"); case MTE_CTRL_TCF_SYNC: return sysfs_emit(buf, "sync\n"); default: return sysfs_emit(buf, "???\n"); } } static ssize_t mte_tcf_preferred_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { u64 tcf; if (sysfs_streq(buf, "async")) tcf = MTE_CTRL_TCF_ASYNC; else if (sysfs_streq(buf, "sync")) tcf = MTE_CTRL_TCF_SYNC; else return -EINVAL; device_lock(dev); per_cpu(mte_tcf_preferred, dev->id) = tcf; device_unlock(dev); return count; } static DEVICE_ATTR_RW(mte_tcf_preferred); static int register_mte_tcf_preferred_sysctl(void) { unsigned int cpu; if (!system_supports_mte()) return 0; for_each_possible_cpu(cpu) { per_cpu(mte_tcf_preferred, cpu) = MTE_CTRL_TCF_ASYNC; device_create_file(get_cpu_device(cpu), &dev_attr_mte_tcf_preferred); } return 0; } subsys_initcall(register_mte_tcf_preferred_sysctl);