swh:1:snp:77163734605b0ec556b01d897b7bb4a7e30d46b6
Tip revision: f40ddce88593482919761f74910f42f4b84c004b authored by Linus Torvalds on 14 February 2021, 22:32:24 UTC
Linux 5.11
Linux 5.11
Tip revision: f40ddce
mte.c
// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2020 ARM Ltd.
*/
#include <linux/bitops.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/mte-kasan.h>
#include <asm/ptrace.h>
#include <asm/sysreg.h>
u64 gcr_kernel_excl __ro_after_init;
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;
}
u8 mte_get_mem_tag(void *addr)
{
if (!system_supports_mte())
return 0xFF;
asm(__MTE_PREAMBLE "ldg %0, [%0]"
: "+r" (addr));
return mte_get_ptr_tag(addr);
}
u8 mte_get_random_tag(void)
{
void *addr;
if (!system_supports_mte())
return 0xFF;
asm(__MTE_PREAMBLE "irg %0, %0"
: "+r" (addr));
return mte_get_ptr_tag(addr);
}
void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
{
void *ptr = addr;
if ((!system_supports_mte()) || (size == 0))
return addr;
/* Make sure that size is MTE granule aligned. */
WARN_ON(size & (MTE_GRANULE_SIZE - 1));
/* Make sure that the address is MTE granule aligned. */
WARN_ON((u64)addr & (MTE_GRANULE_SIZE - 1));
tag = 0xF0 | tag;
ptr = (void *)__tag_set(ptr, tag);
mte_assign_mem_tag_range(ptr, size);
return ptr;
}
void mte_init_tags(u64 max_tag)
{
static bool gcr_kernel_excl_initialized;
if (!gcr_kernel_excl_initialized) {
/*
* The format of the tags in KASAN is 0xFF and in MTE is 0xF.
* This conversion extracts an MTE tag from a KASAN tag.
*/
u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
max_tag), 0);
gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
gcr_kernel_excl_initialized = true;
}
/* Enable the kernel exclude mask for random tags generation. */
write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
}
void mte_enable_kernel(void)
{
/* Enable MTE Sync Mode for EL1. */
sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
isb();
}
static void update_sctlr_el1_tcf0(u64 tcf0)
{
/* ISB required for the kernel uaccess routines */
sysreg_clear_set(sctlr_el1, SCTLR_EL1_TCF0_MASK, tcf0);
isb();
}
static void set_sctlr_el1_tcf0(u64 tcf0)
{
/*
* mte_thread_switch() checks current->thread.sctlr_tcf0 as an
* optimisation. Disable preemption so that it does not see
* the variable update before the SCTLR_EL1.TCF0 one.
*/
preempt_disable();
current->thread.sctlr_tcf0 = tcf0;
update_sctlr_el1_tcf0(tcf0);
preempt_enable();
}
static void update_gcr_el1_excl(u64 excl)
{
/*
* Note that the mask controlled by the user via prctl() is an
* include while GCR_EL1 accepts an exclude mask.
* No need for ISB since this only affects EL0 currently, implicit
* with ERET.
*/
sysreg_clear_set_s(SYS_GCR_EL1, SYS_GCR_EL1_EXCL_MASK, excl);
}
static void set_gcr_el1_excl(u64 excl)
{
current->thread.gcr_user_excl = excl;
/*
* SYS_GCR_EL1 will be set to current->thread.gcr_user_excl value
* by mte_set_user_gcr() in kernel_exit,
*/
}
void flush_mte_state(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 */
set_sctlr_el1_tcf0(SCTLR_EL1_TCF0_NONE);
/* reset tag generation mask */
set_gcr_el1_excl(SYS_GCR_EL1_EXCL_MASK);
}
void mte_thread_switch(struct task_struct *next)
{
if (!system_supports_mte())
return;
/* avoid expensive SCTLR_EL1 accesses if no change */
if (current->thread.sctlr_tcf0 != next->thread.sctlr_tcf0)
update_sctlr_el1_tcf0(next->thread.sctlr_tcf0);
}
void mte_suspend_exit(void)
{
if (!system_supports_mte())
return;
update_gcr_el1_excl(gcr_kernel_excl);
}
long set_mte_ctrl(struct task_struct *task, unsigned long arg)
{
u64 tcf0;
u64 gcr_excl = ~((arg & PR_MTE_TAG_MASK) >> PR_MTE_TAG_SHIFT) &
SYS_GCR_EL1_EXCL_MASK;
if (!system_supports_mte())
return 0;
switch (arg & PR_MTE_TCF_MASK) {
case PR_MTE_TCF_NONE:
tcf0 = SCTLR_EL1_TCF0_NONE;
break;
case PR_MTE_TCF_SYNC:
tcf0 = SCTLR_EL1_TCF0_SYNC;
break;
case PR_MTE_TCF_ASYNC:
tcf0 = SCTLR_EL1_TCF0_ASYNC;
break;
default:
return -EINVAL;
}
if (task != current) {
task->thread.sctlr_tcf0 = tcf0;
task->thread.gcr_user_excl = gcr_excl;
} else {
set_sctlr_el1_tcf0(tcf0);
set_gcr_el1_excl(gcr_excl);
}
return 0;
}
long get_mte_ctrl(struct task_struct *task)
{
unsigned long ret;
u64 incl = ~task->thread.gcr_user_excl & SYS_GCR_EL1_EXCL_MASK;
if (!system_supports_mte())
return 0;
ret = incl << PR_MTE_TAG_SHIFT;
switch (task->thread.sctlr_tcf0) {
case SCTLR_EL1_TCF0_NONE:
ret |= PR_MTE_TCF_NONE;
break;
case SCTLR_EL1_TCF0_SYNC:
ret |= PR_MTE_TCF_SYNC;
break;
case SCTLR_EL1_TCF0_ASYNC:
ret |= PR_MTE_TCF_ASYNC;
break;
}
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;
}