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-rw-r--r--arch/arm64/kernel/mte.c634
1 files changed, 634 insertions, 0 deletions
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
new file mode 100644
index 000000000..e20af03b4
--- /dev/null
+++ b/arch/arm64/kernel/mte.c
@@ -0,0 +1,634 @@
+// 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/uaccess.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 DEFINE_PER_CPU_READ_MOSTLY(u64, mte_tcf_preferred);
+
+#ifdef CONFIG_KASAN_HW_TAGS
+/*
+ * The asynchronous and asymmetric MTE modes have the same behavior for
+ * store operations. This flag is set when either of these modes is enabled.
+ */
+DEFINE_STATIC_KEY_FALSE(mte_async_or_asymm_mode);
+EXPORT_SYMBOL_GPL(mte_async_or_asymm_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)) {
+ set_page_mte_tagged(page);
+ return;
+ }
+ }
+
+ if (!pte_is_tagged)
+ return;
+
+ /*
+ * Test PG_mte_tagged again in case it was racing with another
+ * set_pte_at().
+ */
+ if (!page_mte_tagged(page)) {
+ mte_clear_page_tags(page_address(page));
+ set_page_mte_tagged(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 (!page_mte_tagged(page))
+ 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 (page_mte_tagged(page1) || page_mte_tagged(page2))
+ 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_EL1_TCF_MASK,
+ SYS_FIELD_PREP(SCTLR_EL1, TCF, 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_or_asymm_mode(),
+ "MTE async mode enabled system wide!");
+
+ __mte_enable_kernel("synchronous", SCTLR_EL1_TCF_SYNC);
+}
+
+void mte_enable_kernel_async(void)
+{
+ __mte_enable_kernel("asynchronous", SCTLR_EL1_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_or_asymm_mode())
+ static_branch_enable(&mte_async_or_asymm_mode);
+}
+
+void mte_enable_kernel_asymm(void)
+{
+ if (cpus_have_cap(ARM64_MTE_ASYMM)) {
+ __mte_enable_kernel("asymmetric", SCTLR_EL1_TCF_ASYMM);
+
+ /*
+ * MTE asymm mode behaves as async mode for store
+ * operations. The 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_or_asymm_mode())
+ static_branch_enable(&mte_async_or_asymm_mode);
+ } else {
+ /*
+ * If the CPU does not support MTE asymmetric mode the
+ * kernel falls back on synchronous mode which is the
+ * default for kasan=on.
+ */
+ mte_enable_kernel_sync();
+ }
+}
+#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
+
+/*
+ * This is where we actually resolve the system and process MTE mode
+ * configuration into an actual value in SCTLR_EL1 that affects
+ * userspace.
+ */
+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);
+ /*
+ * If there is no overlap between the system preferred and
+ * program requested values go with what was requested.
+ */
+ resolved_mte_tcf = (mte_ctrl & pref) ? pref : mte_ctrl;
+ sctlr &= ~SCTLR_EL1_TCF0_MASK;
+ /*
+ * Pick an actual setting. The order in which we check for
+ * set bits and map into register values determines our
+ * default order.
+ */
+ if (resolved_mte_tcf & MTE_CTRL_TCF_ASYMM)
+ sctlr |= SYS_FIELD_PREP_ENUM(SCTLR_EL1, TCF0, ASYMM);
+ else if (resolved_mte_tcf & MTE_CTRL_TCF_ASYNC)
+ sctlr |= SYS_FIELD_PREP_ENUM(SCTLR_EL1, TCF0, ASYNC);
+ else if (resolved_mte_tcf & MTE_CTRL_TCF_SYNC)
+ sctlr |= SYS_FIELD_PREP_ENUM(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);
+}
+
+#ifdef CONFIG_KASAN_HW_TAGS
+/* Only called from assembly, silence sparse */
+void __init kasan_hw_tags_enable(struct alt_instr *alt, __le32 *origptr,
+ __le32 *updptr, int nr_inst);
+
+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());
+}
+#endif
+
+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);
+
+ /* TCO may not have been disabled on exception entry for the current task. */
+ mte_disable_tco_entry(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;
+
+ /*
+ * If the system supports it and both sync and async modes are
+ * specified then implicitly enable asymmetric mode.
+ * Userspace could see a mix of both sync and async anyway due
+ * to differing or changing defaults on CPUs.
+ */
+ if (cpus_have_cap(ARM64_MTE_ASYMM) &&
+ (arg & PR_MTE_TCF_ASYNC) &&
+ (arg & PR_MTE_TCF_SYNC))
+ mte_ctrl |= MTE_CTRL_TCF_ASYMM;
+
+ 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(!page_mte_tagged(page));
+
+ /* 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");
+ case MTE_CTRL_TCF_ASYMM:
+ return sysfs_emit(buf, "asymm\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 if (cpus_have_cap(ARM64_MTE_ASYMM) && sysfs_streq(buf, "asymm"))
+ tcf = MTE_CTRL_TCF_ASYMM;
+ 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);
+
+/*
+ * Return 0 on success, the number of bytes not probed otherwise.
+ */
+size_t mte_probe_user_range(const char __user *uaddr, size_t size)
+{
+ const char __user *end = uaddr + size;
+ int err = 0;
+ char val;
+
+ __raw_get_user(val, uaddr, err);
+ if (err)
+ return size;
+
+ uaddr = PTR_ALIGN(uaddr, MTE_GRANULE_SIZE);
+ while (uaddr < end) {
+ /*
+ * A read is sufficient for mte, the caller should have probed
+ * for the pte write permission if required.
+ */
+ __raw_get_user(val, uaddr, err);
+ if (err)
+ return end - uaddr;
+ uaddr += MTE_GRANULE_SIZE;
+ }
+ (void)val;
+
+ return 0;
+}