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- // SPDX-License-Identifier: GPL-2.0-only
- /*
- * Copyright (C) 2020 ARM Ltd.
- */
- #include <linux/bitops.h>
- #include <linux/cpu.h>
- #include <linux/kernel.h>
- #include <linux/mm.h>
- #include <linux/prctl.h>
- #include <linux/sched.h>
- #include <linux/sched/mm.h>
- #include <linux/string.h>
- #include <linux/swap.h>
- #include <linux/swapops.h>
- #include <linux/thread_info.h>
- #include <linux/types.h>
- #include <linux/uio.h>
- #include <asm/barrier.h>
- #include <asm/cpufeature.h>
- #include <asm/mte.h>
- #include <asm/ptrace.h>
- #include <asm/sysreg.h>
- static bool report_fault_once = true;
- 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 *ptep, bool check_swap)
- {
- pte_t old_pte = READ_ONCE(*ptep);
- 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;
- }
- 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();
- mte_clear_page_tags(page_address(page));
- }
- void mte_sync_tags(pte_t *ptep, pte_t pte)
- {
- struct page *page = pte_page(pte);
- long i, nr_pages = compound_nr(page);
- bool check_swap = nr_pages == 1;
- /* if PG_mte_tagged is set, tags have already been initialised */
- for (i = 0; i < nr_pages; i++, page++) {
- if (!test_and_set_bit(PG_mte_tagged, &page->flags))
- mte_sync_page_tags(page, ptep, check_swap);
- }
- }
- 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
- void mte_set_report_once(bool state)
- {
- WRITE_ONCE(report_fault_once, state);
- }
- bool mte_report_once(void)
- {
- return READ_ONCE(report_fault_once);
- }
- #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;
- }
- static void mte_update_gcr_excl(struct task_struct *task)
- {
- /*
- * SYS_GCR_EL1 will be set to current->thread.mte_ctrl value by
- * mte_set_user_gcr() in kernel_exit, but only if KASAN is enabled.
- */
- if (kasan_hw_tags_enabled())
- return;
- write_sysreg_s(
- ((task->thread.mte_ctrl >> MTE_CTRL_GCR_USER_EXCL_SHIFT) &
- SYS_GCR_EL1_EXCL_MASK) | SYS_GCR_EL1_RRND,
- SYS_GCR_EL1);
- }
- void __init kasan_hw_tags_enable(struct alt_instr *alt, __le32 *origptr,
- __le32 *updptr, int nr_inst)
- {
- BUG_ON(nr_inst != 1); /* Branch -> NOP */
- if (kasan_hw_tags_enabled())
- *updptr = cpu_to_le32(aarch64_insn_gen_nop());
- }
- 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);
- mte_update_gcr_excl(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_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();
- }
- 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);
- mte_update_gcr_excl(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);
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