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linux/arch/arm/mm/fault.c
Linus Torvalds 9471f1f2f5 Merge branch 'expand-stack' 
This modifies our user mode stack expansion code to always take the
mmap_lock for writing before modifying the VM layout.

It's actually something we always technically should have done, but
because we didn't strictly need it, we were being lazy ("opportunistic"
sounds so much better, doesn't it?) about things, and had this hack in
place where we would extend the stack vma in-place without doing the
proper locking.

And it worked fine.  We just needed to change vm_start (or, in the case
of grow-up stacks, vm_end) and together with some special ad-hoc locking
using the anon_vma lock and the mm->page_table_lock, it all was fairly
straightforward.

That is, it was all fine until Ruihan Li pointed out that now that the
vma layout uses the maple tree code, we *really* don't just change
vm_start and vm_end any more, and the locking really is broken.  Oops.

It's not actually all _that_ horrible to fix this once and for all, and
do proper locking, but it's a bit painful.  We have basically three
different cases of stack expansion, and they all work just a bit
differently:

 - the common and obvious case is the page fault handling. It's actually
   fairly simple and straightforward, except for the fact that we have
   something like 24 different versions of it, and you end up in a maze
   of twisty little passages, all alike.

 - the simplest case is the execve() code that creates a new stack.
   There are no real locking concerns because it's all in a private new
   VM that hasn't been exposed to anybody, but lockdep still can end up
   unhappy if you get it wrong.

 - and finally, we have GUP and page pinning, which shouldn't really be
   expanding the stack in the first place, but in addition to execve()
   we also use it for ptrace(). And debuggers do want to possibly access
   memory under the stack pointer and thus need to be able to expand the
   stack as a special case.

None of these cases are exactly complicated, but the page fault case in
particular is just repeated slightly differently many many times.  And
ia64 in particular has a fairly complicated situation where you can have
both a regular grow-down stack _and_ a special grow-up stack for the
register backing store.

So to make this slightly more manageable, the bulk of this series is to
first create a helper function for the most common page fault case, and
convert all the straightforward architectures to it.

Thus the new 'lock_mm_and_find_vma()' helper function, which ends up
being used by x86, arm, powerpc, mips, riscv, alpha, arc, csky, hexagon,
loongarch, nios2, sh, sparc32, and xtensa.  So we not only convert more
than half the architectures, we now have more shared code and avoid some
of those twisty little passages.

And largely due to this common helper function, the full diffstat of
this series ends up deleting more lines than it adds.

That still leaves eight architectures (ia64, m68k, microblaze, openrisc,
parisc, s390, sparc64 and um) that end up doing 'expand_stack()'
manually because they are doing something slightly different from the
normal pattern.  Along with the couple of special cases in execve() and
GUP.

So there's a couple of patches that first create 'locked' helper
versions of the stack expansion functions, so that there's a obvious
path forward in the conversion.  The execve() case is then actually
pretty simple, and is a nice cleanup from our old "grow-up stackls are
special, because at execve time even they grow down".

The #ifdef CONFIG_STACK_GROWSUP in that code just goes away, because
it's just more straightforward to write out the stack expansion there
manually, instead od having get_user_pages_remote() do it for us in some
situations but not others and have to worry about locking rules for GUP.

And the final step is then to just convert the remaining odd cases to a
new world order where 'expand_stack()' is called with the mmap_lock held
for reading, but where it might drop it and upgrade it to a write, only
to return with it held for reading (in the success case) or with it
completely dropped (in the failure case).

In the process, we remove all the stack expansion from GUP (where
dropping the lock wouldn't be ok without special rules anyway), and add
it in manually to __access_remote_vm() for ptrace().

Thanks to Adrian Glaubitz and Frank Scheiner who tested the ia64 cases.
Everything else here felt pretty straightforward, but the ia64 rules for
stack expansion are really quite odd and very different from everything
else.  Also thanks to Vegard Nossum who caught me getting one of those
odd conditions entirely the wrong way around.

Anyway, I think I want to actually move all the stack expansion code to
a whole new file of its own, rather than have it split up between
mm/mmap.c and mm/memory.c, but since this will have to be backported to
the initial maple tree vma introduction anyway, I tried to keep the
patches _fairly_ minimal.

Also, while I don't think it's valid to expand the stack from GUP, the
final patch in here is a "warn if some crazy GUP user wants to try to
expand the stack" patch.  That one will be reverted before the final
release, but it's left to catch any odd cases during the merge window
and release candidates.

Reported-by: Ruihan Li <lrh2000@pku.edu.cn>

* branch 'expand-stack':
  gup: add warning if some caller would seem to want stack expansion
  mm: always expand the stack with the mmap write lock held
  execve: expand new process stack manually ahead of time
  mm: make find_extend_vma() fail if write lock not held
  powerpc/mm: convert coprocessor fault to lock_mm_and_find_vma()
  mm/fault: convert remaining simple cases to lock_mm_and_find_vma()
  arm/mm: Convert to using lock_mm_and_find_vma()
  riscv/mm: Convert to using lock_mm_and_find_vma()
  mips/mm: Convert to using lock_mm_and_find_vma()
  powerpc/mm: Convert to using lock_mm_and_find_vma()
  arm64/mm: Convert to using lock_mm_and_find_vma()
  mm: make the page fault mmap locking killable
  mm: introduce new 'lock_mm_and_find_vma()' page fault helper
2023-06-28 20:35:21 -07:00

612 lines
14 KiB
C
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// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/arch/arm/mm/fault.c
*
* Copyright (C) 1995 Linus Torvalds
* Modifications for ARM processor (c) 1995-2004 Russell King
*/
#include <linux/extable.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/hardirq.h>
#include <linux/init.h>
#include <linux/kprobes.h>
#include <linux/uaccess.h>
#include <linux/page-flags.h>
#include <linux/sched/signal.h>
#include <linux/sched/debug.h>
#include <linux/highmem.h>
#include <linux/perf_event.h>
#include <linux/kfence.h>
#include <asm/system_misc.h>
#include <asm/system_info.h>
#include <asm/tlbflush.h>
#include "fault.h"
#ifdef CONFIG_MMU
/*
* This is useful to dump out the page tables associated with
* 'addr' in mm 'mm'.
*/
void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
{
pgd_t *pgd;
if (!mm)
mm = &init_mm;
pgd = pgd_offset(mm, addr);
printk("%s[%08lx] *pgd=%08llx", lvl, addr, (long long)pgd_val(*pgd));
do {
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
p4d = p4d_offset(pgd, addr);
if (p4d_none(*p4d))
break;
if (p4d_bad(*p4d)) {
pr_cont("(bad)");
break;
}
pud = pud_offset(p4d, addr);
if (PTRS_PER_PUD != 1)
pr_cont(", *pud=%08llx", (long long)pud_val(*pud));
if (pud_none(*pud))
break;
if (pud_bad(*pud)) {
pr_cont("(bad)");
break;
}
pmd = pmd_offset(pud, addr);
if (PTRS_PER_PMD != 1)
pr_cont(", *pmd=%08llx", (long long)pmd_val(*pmd));
if (pmd_none(*pmd))
break;
if (pmd_bad(*pmd)) {
pr_cont("(bad)");
break;
}
/* We must not map this if we have highmem enabled */
if (PageHighMem(pfn_to_page(pmd_val(*pmd) >> PAGE_SHIFT)))
break;
pte = pte_offset_map(pmd, addr);
if (!pte)
break;
pr_cont(", *pte=%08llx", (long long)pte_val(*pte));
#ifndef CONFIG_ARM_LPAE
pr_cont(", *ppte=%08llx",
(long long)pte_val(pte[PTE_HWTABLE_PTRS]));
#endif
pte_unmap(pte);
} while(0);
pr_cont("\n");
}
#else /* CONFIG_MMU */
void show_pte(const char *lvl, struct mm_struct *mm, unsigned long addr)
{ }
#endif /* CONFIG_MMU */
static inline bool is_write_fault(unsigned int fsr)
{
return (fsr & FSR_WRITE) && !(fsr & FSR_CM);
}
static inline bool is_translation_fault(unsigned int fsr)
{
int fs = fsr_fs(fsr);
#ifdef CONFIG_ARM_LPAE
if ((fs & FS_MMU_NOLL_MASK) == FS_TRANS_NOLL)
return true;
#else
if (fs == FS_L1_TRANS || fs == FS_L2_TRANS)
return true;
#endif
return false;
}
static void die_kernel_fault(const char *msg, struct mm_struct *mm,
unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
{
bust_spinlocks(1);
pr_alert("8<--- cut here ---\n");
pr_alert("Unable to handle kernel %s at virtual address %08lx when %s\n",
msg, addr, fsr & FSR_LNX_PF ? "execute" :
fsr & FSR_WRITE ? "write" : "read");
show_pte(KERN_ALERT, mm, addr);
die("Oops", regs, fsr);
bust_spinlocks(0);
make_task_dead(SIGKILL);
}
/*
* Oops. The kernel tried to access some page that wasn't present.
*/
static void
__do_kernel_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
{
const char *msg;
/*
* Are we prepared to handle this kernel fault?
*/
if (fixup_exception(regs))
return;
/*
* No handler, we'll have to terminate things with extreme prejudice.
*/
if (addr < PAGE_SIZE) {
msg = "NULL pointer dereference";
} else {
if (is_translation_fault(fsr) &&
kfence_handle_page_fault(addr, is_write_fault(fsr), regs))
return;
msg = "paging request";
}
die_kernel_fault(msg, mm, addr, fsr, regs);
}
/*
* Something tried to access memory that isn't in our memory map..
* User mode accesses just cause a SIGSEGV
*/
static void
__do_user_fault(unsigned long addr, unsigned int fsr, unsigned int sig,
int code, struct pt_regs *regs)
{
struct task_struct *tsk = current;
if (addr > TASK_SIZE)
harden_branch_predictor();
#ifdef CONFIG_DEBUG_USER
if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
((user_debug & UDBG_BUS) && (sig == SIGBUS))) {
pr_err("8<--- cut here ---\n");
pr_err("%s: unhandled page fault (%d) at 0x%08lx, code 0x%03x\n",
tsk->comm, sig, addr, fsr);
show_pte(KERN_ERR, tsk->mm, addr);
show_regs(regs);
}
#endif
#ifndef CONFIG_KUSER_HELPERS
if ((sig == SIGSEGV) && ((addr & PAGE_MASK) == 0xffff0000))
printk_ratelimited(KERN_DEBUG
"%s: CONFIG_KUSER_HELPERS disabled at 0x%08lx\n",
tsk->comm, addr);
#endif
tsk->thread.address = addr;
tsk->thread.error_code = fsr;
tsk->thread.trap_no = 14;
force_sig_fault(sig, code, (void __user *)addr);
}
void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
struct task_struct *tsk = current;
struct mm_struct *mm = tsk->active_mm;
/*
* If we are in kernel mode at this point, we
* have no context to handle this fault with.
*/
if (user_mode(regs))
__do_user_fault(addr, fsr, SIGSEGV, SEGV_MAPERR, regs);
else
__do_kernel_fault(mm, addr, fsr, regs);
}
#ifdef CONFIG_MMU
#define VM_FAULT_BADMAP ((__force vm_fault_t)0x010000)
#define VM_FAULT_BADACCESS ((__force vm_fault_t)0x020000)
static inline bool is_permission_fault(unsigned int fsr)
{
int fs = fsr_fs(fsr);
#ifdef CONFIG_ARM_LPAE
if ((fs & FS_MMU_NOLL_MASK) == FS_PERM_NOLL)
return true;
#else
if (fs == FS_L1_PERM || fs == FS_L2_PERM)
return true;
#endif
return false;
}
static int __kprobes
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
int sig, code;
vm_fault_t fault;
unsigned int flags = FAULT_FLAG_DEFAULT;
unsigned long vm_flags = VM_ACCESS_FLAGS;
if (kprobe_page_fault(regs, fsr))
return 0;
/* Enable interrupts if they were enabled in the parent context. */
if (interrupts_enabled(regs))
local_irq_enable();
/*
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
if (faulthandler_disabled() || !mm)
goto no_context;
if (user_mode(regs))
flags |= FAULT_FLAG_USER;
if (is_write_fault(fsr)) {
flags |= FAULT_FLAG_WRITE;
vm_flags = VM_WRITE;
}
if (fsr & FSR_LNX_PF) {
vm_flags = VM_EXEC;
if (is_permission_fault(fsr) && !user_mode(regs))
die_kernel_fault("execution of memory",
mm, addr, fsr, regs);
}
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
retry:
vma = lock_mm_and_find_vma(mm, addr, regs);
if (unlikely(!vma)) {
fault = VM_FAULT_BADMAP;
goto bad_area;
}
/*
* ok, we have a good vm_area for this memory access, check the
* permissions on the VMA allow for the fault which occurred.
*/
if (!(vma->vm_flags & vm_flags))
fault = VM_FAULT_BADACCESS;
else
fault = handle_mm_fault(vma, addr & PAGE_MASK, flags, regs);
/* If we need to retry but a fatal signal is pending, handle the
* signal first. We do not need to release the mmap_lock because
* it would already be released in __lock_page_or_retry in
* mm/filemap.c. */
if (fault_signal_pending(fault, regs)) {
if (!user_mode(regs))
goto no_context;
return 0;
}
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
return 0;
if (!(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_RETRY) {
flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
mmap_read_unlock(mm);
/*
* Handle the "normal" case first - VM_FAULT_MAJOR
*/
if (likely(!(fault & (VM_FAULT_ERROR | VM_FAULT_BADMAP | VM_FAULT_BADACCESS))))
return 0;
bad_area:
/*
* If we are in kernel mode at this point, we
* have no context to handle this fault with.
*/
if (!user_mode(regs))
goto no_context;
if (fault & VM_FAULT_OOM) {
/*
* We ran out of memory, call the OOM killer, and return to
* userspace (which will retry the fault, or kill us if we
* got oom-killed)
*/
pagefault_out_of_memory();
return 0;
}
if (fault & VM_FAULT_SIGBUS) {
/*
* We had some memory, but were unable to
* successfully fix up this page fault.
*/
sig = SIGBUS;
code = BUS_ADRERR;
} else {
/*
* Something tried to access memory that
* isn't in our memory map..
*/
sig = SIGSEGV;
code = fault == VM_FAULT_BADACCESS ?
SEGV_ACCERR : SEGV_MAPERR;
}
__do_user_fault(addr, fsr, sig, code, regs);
return 0;
no_context:
__do_kernel_fault(mm, addr, fsr, regs);
return 0;
}
#else /* CONFIG_MMU */
static int
do_page_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
return 0;
}
#endif /* CONFIG_MMU */
/*
* First Level Translation Fault Handler
*
* We enter here because the first level page table doesn't contain
* a valid entry for the address.
*
* If the address is in kernel space (>= TASK_SIZE), then we are
* probably faulting in the vmalloc() area.
*
* If the init_task's first level page tables contains the relevant
* entry, we copy the it to this task. If not, we send the process
* a signal, fixup the exception, or oops the kernel.
*
* NOTE! We MUST NOT take any locks for this case. We may be in an
* interrupt or a critical region, and should only copy the information
* from the master page table, nothing more.
*/
#ifdef CONFIG_MMU
static int __kprobes
do_translation_fault(unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
{
unsigned int index;
pgd_t *pgd, *pgd_k;
p4d_t *p4d, *p4d_k;
pud_t *pud, *pud_k;
pmd_t *pmd, *pmd_k;
if (addr < TASK_SIZE)
return do_page_fault(addr, fsr, regs);
if (user_mode(regs))
goto bad_area;
index = pgd_index(addr);
pgd = cpu_get_pgd() + index;
pgd_k = init_mm.pgd + index;
p4d = p4d_offset(pgd, addr);
p4d_k = p4d_offset(pgd_k, addr);
if (p4d_none(*p4d_k))
goto bad_area;
if (!p4d_present(*p4d))
set_p4d(p4d, *p4d_k);
pud = pud_offset(p4d, addr);
pud_k = pud_offset(p4d_k, addr);
if (pud_none(*pud_k))
goto bad_area;
if (!pud_present(*pud))
set_pud(pud, *pud_k);
pmd = pmd_offset(pud, addr);
pmd_k = pmd_offset(pud_k, addr);
#ifdef CONFIG_ARM_LPAE
/*
* Only one hardware entry per PMD with LPAE.
*/
index = 0;
#else
/*
* On ARM one Linux PGD entry contains two hardware entries (see page
* tables layout in pgtable.h). We normally guarantee that we always
* fill both L1 entries. But create_mapping() doesn't follow the rule.
* It can create inidividual L1 entries, so here we have to call
* pmd_none() check for the entry really corresponded to address, not
* for the first of pair.
*/
index = (addr >> SECTION_SHIFT) & 1;
#endif
if (pmd_none(pmd_k[index]))
goto bad_area;
copy_pmd(pmd, pmd_k);
return 0;
bad_area:
do_bad_area(addr, fsr, regs);
return 0;
}
#else /* CONFIG_MMU */
static int
do_translation_fault(unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
{
return 0;
}
#endif /* CONFIG_MMU */
/*
* Some section permission faults need to be handled gracefully.
* They can happen due to a __{get,put}_user during an oops.
*/
#ifndef CONFIG_ARM_LPAE
static int
do_sect_fault(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
do_bad_area(addr, fsr, regs);
return 0;
}
#endif /* CONFIG_ARM_LPAE */
/*
* This abort handler always returns "fault".
*/
static int
do_bad(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
return 1;
}
struct fsr_info {
int (*fn)(unsigned long addr, unsigned int fsr, struct pt_regs *regs);
int sig;
int code;
const char *name;
};
/* FSR definition */
#ifdef CONFIG_ARM_LPAE
#include "fsr-3level.c"
#else
#include "fsr-2level.c"
#endif
void __init
hook_fault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
int sig, int code, const char *name)
{
if (nr < 0 || nr >= ARRAY_SIZE(fsr_info))
BUG();
fsr_info[nr].fn = fn;
fsr_info[nr].sig = sig;
fsr_info[nr].code = code;
fsr_info[nr].name = name;
}
/*
* Dispatch a data abort to the relevant handler.
*/
asmlinkage void
do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
{
const struct fsr_info *inf = fsr_info + fsr_fs(fsr);
if (!inf->fn(addr, fsr & ~FSR_LNX_PF, regs))
return;
pr_alert("8<--- cut here ---\n");
pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
inf->name, fsr, addr);
show_pte(KERN_ALERT, current->mm, addr);
arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
fsr, 0);
}
void __init
hook_ifault_code(int nr, int (*fn)(unsigned long, unsigned int, struct pt_regs *),
int sig, int code, const char *name)
{
if (nr < 0 || nr >= ARRAY_SIZE(ifsr_info))
BUG();
ifsr_info[nr].fn = fn;
ifsr_info[nr].sig = sig;
ifsr_info[nr].code = code;
ifsr_info[nr].name = name;
}
asmlinkage void
do_PrefetchAbort(unsigned long addr, unsigned int ifsr, struct pt_regs *regs)
{
const struct fsr_info *inf = ifsr_info + fsr_fs(ifsr);
if (!inf->fn(addr, ifsr | FSR_LNX_PF, regs))
return;
pr_alert("Unhandled prefetch abort: %s (0x%03x) at 0x%08lx\n",
inf->name, ifsr, addr);
arm_notify_die("", regs, inf->sig, inf->code, (void __user *)addr,
ifsr, 0);
}
/*
* Abort handler to be used only during first unmasking of asynchronous aborts
* on the boot CPU. This makes sure that the machine will not die if the
* firmware/bootloader left an imprecise abort pending for us to trip over.
*/
static int __init early_abort_handler(unsigned long addr, unsigned int fsr,
struct pt_regs *regs)
{
pr_warn("Hit pending asynchronous external abort (FSR=0x%08x) during "
"first unmask, this is most likely caused by a "
"firmware/bootloader bug.\n", fsr);
return 0;
}
void __init early_abt_enable(void)
{
fsr_info[FSR_FS_AEA].fn = early_abort_handler;
local_abt_enable();
fsr_info[FSR_FS_AEA].fn = do_bad;
}
#ifndef CONFIG_ARM_LPAE
static int __init exceptions_init(void)
{
if (cpu_architecture() >= CPU_ARCH_ARMv6) {
hook_fault_code(4, do_translation_fault, SIGSEGV, SEGV_MAPERR,
"I-cache maintenance fault");
}
if (cpu_architecture() >= CPU_ARCH_ARMv7) {
/*
* TODO: Access flag faults introduced in ARMv6K.
* Runtime check for 'K' extension is needed
*/
hook_fault_code(3, do_bad, SIGSEGV, SEGV_MAPERR,
"section access flag fault");
hook_fault_code(6, do_bad, SIGSEGV, SEGV_MAPERR,
"section access flag fault");
}
return 0;
}
arch_initcall(exceptions_init);
#endif
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