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linux/arch/sparc/mm/fault_64.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

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// SPDX-License-Identifier: GPL-2.0
/*
* arch/sparc64/mm/fault.c: Page fault handlers for the 64-bit Sparc.
*
* Copyright (C) 1996, 2008 David S. Miller (davem@davemloft.net)
* Copyright (C) 1997, 1999 Jakub Jelinek (jj@ultra.linux.cz)
*/
#include <asm/head.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/signal.h>
#include <linux/mm.h>
#include <linux/extable.h>
#include <linux/init.h>
#include <linux/perf_event.h>
#include <linux/interrupt.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/percpu.h>
#include <linux/context_tracking.h>
#include <linux/uaccess.h>
#include <asm/page.h>
#include <asm/openprom.h>
#include <asm/oplib.h>
#include <asm/asi.h>
#include <asm/lsu.h>
#include <asm/sections.h>
#include <asm/mmu_context.h>
#include <asm/setup.h>
int show_unhandled_signals = 1;
static void __kprobes unhandled_fault(unsigned long address,
struct task_struct *tsk,
struct pt_regs *regs)
{
if ((unsigned long) address < PAGE_SIZE) {
printk(KERN_ALERT "Unable to handle kernel NULL "
"pointer dereference\n");
} else {
printk(KERN_ALERT "Unable to handle kernel paging request "
"at virtual address %016lx\n", (unsigned long)address);
}
printk(KERN_ALERT "tsk->{mm,active_mm}->context = %016lx\n",
(tsk->mm ?
CTX_HWBITS(tsk->mm->context) :
CTX_HWBITS(tsk->active_mm->context)));
printk(KERN_ALERT "tsk->{mm,active_mm}->pgd = %016lx\n",
(tsk->mm ? (unsigned long) tsk->mm->pgd :
(unsigned long) tsk->active_mm->pgd));
die_if_kernel("Oops", regs);
}
static void __kprobes bad_kernel_pc(struct pt_regs *regs, unsigned long vaddr)
{
printk(KERN_CRIT "OOPS: Bogus kernel PC [%016lx] in fault handler\n",
regs->tpc);
printk(KERN_CRIT "OOPS: RPC [%016lx]\n", regs->u_regs[15]);
printk("OOPS: RPC <%pS>\n", (void *) regs->u_regs[15]);
printk(KERN_CRIT "OOPS: Fault was to vaddr[%lx]\n", vaddr);
dump_stack();
unhandled_fault(regs->tpc, current, regs);
}
/*
* We now make sure that mmap_lock is held in all paths that call
* this. Additionally, to prevent kswapd from ripping ptes from
* under us, raise interrupts around the time that we look at the
* pte, kswapd will have to wait to get his smp ipi response from
* us. vmtruncate likewise. This saves us having to get pte lock.
*/
static unsigned int get_user_insn(unsigned long tpc)
{
pgd_t *pgdp = pgd_offset(current->mm, tpc);
p4d_t *p4dp;
pud_t *pudp;
pmd_t *pmdp;
pte_t *ptep, pte;
unsigned long pa;
u32 insn = 0;
if (pgd_none(*pgdp) || unlikely(pgd_bad(*pgdp)))
goto out;
p4dp = p4d_offset(pgdp, tpc);
if (p4d_none(*p4dp) || unlikely(p4d_bad(*p4dp)))
goto out;
pudp = pud_offset(p4dp, tpc);
if (pud_none(*pudp) || unlikely(pud_bad(*pudp)))
goto out;
/* This disables preemption for us as well. */
local_irq_disable();
pmdp = pmd_offset(pudp, tpc);
again:
if (pmd_none(*pmdp) || unlikely(pmd_bad(*pmdp)))
goto out_irq_enable;
#if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)
if (is_hugetlb_pmd(*pmdp)) {
pa = pmd_pfn(*pmdp) << PAGE_SHIFT;
pa += tpc & ~HPAGE_MASK;
/* Use phys bypass so we don't pollute dtlb/dcache. */
__asm__ __volatile__("lduwa [%1] %2, %0"
: "=r" (insn)
: "r" (pa), "i" (ASI_PHYS_USE_EC));
} else
#endif
{
ptep = pte_offset_map(pmdp, tpc);
if (!ptep)
goto again;
pte = *ptep;
if (pte_present(pte)) {
pa = (pte_pfn(pte) << PAGE_SHIFT);
pa += (tpc & ~PAGE_MASK);
/* Use phys bypass so we don't pollute dtlb/dcache. */
__asm__ __volatile__("lduwa [%1] %2, %0"
: "=r" (insn)
: "r" (pa), "i" (ASI_PHYS_USE_EC));
}
pte_unmap(ptep);
}
out_irq_enable:
local_irq_enable();
out:
return insn;
}
static inline void
show_signal_msg(struct pt_regs *regs, int sig, int code,
unsigned long address, struct task_struct *tsk)
{
if (!unhandled_signal(tsk, sig))
return;
if (!printk_ratelimit())
return;
printk("%s%s[%d]: segfault at %lx ip %px (rpc %px) sp %px error %x",
task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
tsk->comm, task_pid_nr(tsk), address,
(void *)regs->tpc, (void *)regs->u_regs[UREG_I7],
(void *)regs->u_regs[UREG_FP], code);
print_vma_addr(KERN_CONT " in ", regs->tpc);
printk(KERN_CONT "\n");
}
static void do_fault_siginfo(int code, int sig, struct pt_regs *regs,
unsigned long fault_addr, unsigned int insn,
int fault_code)
{
unsigned long addr;
if (fault_code & FAULT_CODE_ITLB) {
addr = regs->tpc;
} else {
/* If we were able to probe the faulting instruction, use it
* to compute a precise fault address. Otherwise use the fault
* time provided address which may only have page granularity.
*/
if (insn)
addr = compute_effective_address(regs, insn, 0);
else
addr = fault_addr;
}
if (unlikely(show_unhandled_signals))
show_signal_msg(regs, sig, code, addr, current);
force_sig_fault(sig, code, (void __user *) addr);
}
static unsigned int get_fault_insn(struct pt_regs *regs, unsigned int insn)
{
if (!insn) {
if (!regs->tpc || (regs->tpc & 0x3))
return 0;
if (regs->tstate & TSTATE_PRIV) {
insn = *(unsigned int *) regs->tpc;
} else {
insn = get_user_insn(regs->tpc);
}
}
return insn;
}
static void __kprobes do_kernel_fault(struct pt_regs *regs, int si_code,
int fault_code, unsigned int insn,
unsigned long address)
{
unsigned char asi = ASI_P;
if ((!insn) && (regs->tstate & TSTATE_PRIV))
goto cannot_handle;
/* If user insn could be read (thus insn is zero), that
* is fine. We will just gun down the process with a signal
* in that case.
*/
if (!(fault_code & (FAULT_CODE_WRITE|FAULT_CODE_ITLB)) &&
(insn & 0xc0800000) == 0xc0800000) {
if (insn & 0x2000)
asi = (regs->tstate >> 24);
else
asi = (insn >> 5);
if ((asi & 0xf2) == 0x82) {
if (insn & 0x1000000) {
handle_ldf_stq(insn, regs);
} else {
/* This was a non-faulting load. Just clear the
* destination register(s) and continue with the next
* instruction. -jj
*/
handle_ld_nf(insn, regs);
}
return;
}
}
/* Is this in ex_table? */
if (regs->tstate & TSTATE_PRIV) {
const struct exception_table_entry *entry;
entry = search_exception_tables(regs->tpc);
if (entry) {
regs->tpc = entry->fixup;
regs->tnpc = regs->tpc + 4;
return;
}
} else {
/* The si_code was set to make clear whether
* this was a SEGV_MAPERR or SEGV_ACCERR fault.
*/
do_fault_siginfo(si_code, SIGSEGV, regs, address, insn, fault_code);
return;
}
cannot_handle:
unhandled_fault (address, current, regs);
}
static void noinline __kprobes bogus_32bit_fault_tpc(struct pt_regs *regs)
{
static int times;
if (times++ < 10)
printk(KERN_ERR "FAULT[%s:%d]: 32-bit process reports "
"64-bit TPC [%lx]\n",
current->comm, current->pid,
regs->tpc);
show_regs(regs);
}
asmlinkage void __kprobes do_sparc64_fault(struct pt_regs *regs)
{
enum ctx_state prev_state = exception_enter();
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
unsigned int insn = 0;
int si_code, fault_code;
vm_fault_t fault;
unsigned long address, mm_rss;
unsigned int flags = FAULT_FLAG_DEFAULT;
fault_code = get_thread_fault_code();
if (kprobe_page_fault(regs, 0))
goto exit_exception;
si_code = SEGV_MAPERR;
address = current_thread_info()->fault_address;
if ((fault_code & FAULT_CODE_ITLB) &&
(fault_code & FAULT_CODE_DTLB))
BUG();
if (test_thread_flag(TIF_32BIT)) {
if (!(regs->tstate & TSTATE_PRIV)) {
if (unlikely((regs->tpc >> 32) != 0)) {
bogus_32bit_fault_tpc(regs);
goto intr_or_no_mm;
}
}
if (unlikely((address >> 32) != 0))
goto intr_or_no_mm;
}
if (regs->tstate & TSTATE_PRIV) {
unsigned long tpc = regs->tpc;
/* Sanity check the PC. */
if ((tpc >= KERNBASE && tpc < (unsigned long) __init_end) ||
(tpc >= MODULES_VADDR && tpc < MODULES_END)) {
/* Valid, no problems... */
} else {
bad_kernel_pc(regs, address);
goto exit_exception;
}
} else
flags |= FAULT_FLAG_USER;
/*
* If we're in an interrupt or have no user
* context, we must not take the fault..
*/
if (faulthandler_disabled() || !mm)
goto intr_or_no_mm;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
if (!mmap_read_trylock(mm)) {
if ((regs->tstate & TSTATE_PRIV) &&
!search_exception_tables(regs->tpc)) {
insn = get_fault_insn(regs, insn);
goto handle_kernel_fault;
}
retry:
mmap_read_lock(mm);
}
if (fault_code & FAULT_CODE_BAD_RA)
goto do_sigbus;
vma = find_vma(mm, address);
if (!vma)
goto bad_area;
/* Pure DTLB misses do not tell us whether the fault causing
* load/store/atomic was a write or not, it only says that there
* was no match. So in such a case we (carefully) read the
* instruction to try and figure this out. It's an optimization
* so it's ok if we can't do this.
*
* Special hack, window spill/fill knows the exact fault type.
*/
if (((fault_code &
(FAULT_CODE_DTLB | FAULT_CODE_WRITE | FAULT_CODE_WINFIXUP)) == FAULT_CODE_DTLB) &&
(vma->vm_flags & VM_WRITE) != 0) {
insn = get_fault_insn(regs, 0);
if (!insn)
goto continue_fault;
/* All loads, stores and atomics have bits 30 and 31 both set
* in the instruction. Bit 21 is set in all stores, but we
* have to avoid prefetches which also have bit 21 set.
*/
if ((insn & 0xc0200000) == 0xc0200000 &&
(insn & 0x01780000) != 0x01680000) {
/* Don't bother updating thread struct value,
* because update_mmu_cache only cares which tlb
* the access came from.
*/
fault_code |= FAULT_CODE_WRITE;
}
}
continue_fault:
if (vma->vm_start <= address)
goto good_area;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto bad_area;
if (!(fault_code & FAULT_CODE_WRITE)) {
/* Non-faulting loads shouldn't expand stack. */
insn = get_fault_insn(regs, insn);
if ((insn & 0xc0800000) == 0xc0800000) {
unsigned char asi;
if (insn & 0x2000)
asi = (regs->tstate >> 24);
else
asi = (insn >> 5);
if ((asi & 0xf2) == 0x82)
goto bad_area;
}
}
vma = expand_stack(mm, address);
if (!vma)
goto bad_area_nosemaphore;
/*
* Ok, we have a good vm_area for this memory access, so
* we can handle it..
*/
good_area:
si_code = SEGV_ACCERR;
/* If we took a ITLB miss on a non-executable page, catch
* that here.
*/
if ((fault_code & FAULT_CODE_ITLB) && !(vma->vm_flags & VM_EXEC)) {
WARN(address != regs->tpc,
"address (%lx) != regs->tpc (%lx)\n", address, regs->tpc);
WARN_ON(regs->tstate & TSTATE_PRIV);
goto bad_area;
}
if (fault_code & FAULT_CODE_WRITE) {
if (!(vma->vm_flags & VM_WRITE))
goto bad_area;
/* Spitfire has an icache which does not snoop
* processor stores. Later processors do...
*/
if (tlb_type == spitfire &&
(vma->vm_flags & VM_EXEC) != 0 &&
vma->vm_file != NULL)
set_thread_fault_code(fault_code |
FAULT_CODE_BLKCOMMIT);
flags |= FAULT_FLAG_WRITE;
} else {
/* Allow reads even for write-only mappings */
if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
goto bad_area;
}
fault = handle_mm_fault(vma, address, flags, regs);
if (fault_signal_pending(fault, regs)) {
if (regs->tstate & TSTATE_PRIV) {
insn = get_fault_insn(regs, insn);
goto handle_kernel_fault;
}
goto exit_exception;
}
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
goto lock_released;
if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM)
goto out_of_memory;
else if (fault & VM_FAULT_SIGSEGV)
goto bad_area;
else if (fault & VM_FAULT_SIGBUS)
goto do_sigbus;
BUG();
}
if (fault & VM_FAULT_RETRY) {
flags |= FAULT_FLAG_TRIED;
/* No need to mmap_read_unlock(mm) as we would
* have already released it in __lock_page_or_retry
* in mm/filemap.c.
*/
goto retry;
}
mmap_read_unlock(mm);
lock_released:
mm_rss = get_mm_rss(mm);
#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
mm_rss -= (mm->context.thp_pte_count * (HPAGE_SIZE / PAGE_SIZE));
#endif
if (unlikely(mm_rss >
mm->context.tsb_block[MM_TSB_BASE].tsb_rss_limit))
tsb_grow(mm, MM_TSB_BASE, mm_rss);
#if defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)
mm_rss = mm->context.hugetlb_pte_count + mm->context.thp_pte_count;
mm_rss *= REAL_HPAGE_PER_HPAGE;
if (unlikely(mm_rss >
mm->context.tsb_block[MM_TSB_HUGE].tsb_rss_limit)) {
if (mm->context.tsb_block[MM_TSB_HUGE].tsb)
tsb_grow(mm, MM_TSB_HUGE, mm_rss);
else
hugetlb_setup(regs);
}
#endif
exit_exception:
exception_exit(prev_state);
return;
/*
* Something tried to access memory that isn't in our memory map..
* Fix it, but check if it's kernel or user first..
*/
bad_area:
mmap_read_unlock(mm);
bad_area_nosemaphore:
insn = get_fault_insn(regs, insn);
handle_kernel_fault:
do_kernel_fault(regs, si_code, fault_code, insn, address);
goto exit_exception;
/*
* We ran out of memory, or some other thing happened to us that made
* us unable to handle the page fault gracefully.
*/
out_of_memory:
insn = get_fault_insn(regs, insn);
mmap_read_unlock(mm);
if (!(regs->tstate & TSTATE_PRIV)) {
pagefault_out_of_memory();
goto exit_exception;
}
goto handle_kernel_fault;
intr_or_no_mm:
insn = get_fault_insn(regs, 0);
goto handle_kernel_fault;
do_sigbus:
insn = get_fault_insn(regs, insn);
mmap_read_unlock(mm);
/*
* Send a sigbus, regardless of whether we were in kernel
* or user mode.
*/
do_fault_siginfo(BUS_ADRERR, SIGBUS, regs, address, insn, fault_code);
/* Kernel mode? Handle exceptions or die */
if (regs->tstate & TSTATE_PRIV)
goto handle_kernel_fault;
}
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