linux-stable/arch/arm64/kernel/mte.c
Vincenzo Frascino ec0288369f arm64: mte: Add asymmetric mode support
MTE provides an asymmetric mode for detecting tag exceptions. In
particular, when such a mode is present, the CPU triggers a fault
on a tag mismatch during a load operation and asynchronously updates
a register when a tag mismatch is detected during a store operation.

Add support for MTE asymmetric mode.

Note: If the CPU does not support MTE asymmetric mode the kernel falls
back on synchronous mode which is the default for kasan=on.

Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://lore.kernel.org/r/20211006154751.4463-5-vincenzo.frascino@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
2021-10-07 09:30:24 +01:00

511 lines
12 KiB
C

// 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 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))
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();
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_and_set_bit(PG_mte_tagged, &page->flags))
mte_sync_page_tags(page, old_pte, check_swap,
pte_is_tagged);
}
}
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_or_asymm_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_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_ELx_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
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);