// SPDX-License-Identifier: GPL-2.0-or-later
/*
* PowerPC version
* Copyright (C) 1995-1996 Gary Thomas ([email protected])
*
* Derived from "arch/i386/mm/fault.c"
* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
*
* Modified by Cort Dougan and Paul Mackerras.
*
* Modified for PPC64 by Dave Engebretsen ([email protected])
*/
#include <linux/signal.h>
#include <linux/sched.h>
#include <linux/sched/task_stack.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/pagemap.h>
#include <linux/ptrace.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/highmem.h>
#include <linux/extable.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/perf_event.h>
#include <linux/ratelimit.h>
#include <linux/context_tracking.h>
#include <linux/hugetlb.h>
#include <linux/uaccess.h>
#include <linux/kfence.h>
#include <linux/pkeys.h>
#include <asm/firmware.h>
#include <asm/interrupt.h>
#include <asm/page.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/siginfo.h>
#include <asm/debug.h>
#include <asm/kup.h>
#include <asm/inst.h>
/*
* do_page_fault error handling helpers
*/
static int
__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
{
/*
* If we are in kernel mode, bail out with a SEGV, this will
* be caught by the assembly which will restore the non-volatile
* registers before calling bad_page_fault()
*/
if (!user_mode(regs))
return SIGSEGV;
_exception(SIGSEGV, regs, si_code, address);
return 0;
}
static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
{
return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
}
static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code,
struct mm_struct *mm, struct vm_area_struct *vma)
{
/*
* Something tried to access memory that isn't in our memory map..
* Fix it, but check if it's kernel or user first..
*/
if (mm)
mmap_read_unlock(mm);
else
vma_end_read(vma);
return __bad_area_nosemaphore(regs, address, si_code);
}
static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
struct mm_struct *mm,
struct vm_area_struct *vma)
{
int pkey;
/*
* We don't try to fetch the pkey from page table because reading
* page table without locking doesn't guarantee stable pte value.
* Hence the pkey value that we return to userspace can be different
* from the pkey that actually caused access error.
*
* It does *not* guarantee that the VMA we find here
* was the one that we faulted on.
*
* 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
* 2. T1 : set AMR to deny access to pkey=4, touches, page
* 3. T1 : faults...
* 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
* 5. T1 : enters fault handler, takes mmap_lock, etc...
* 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
* faulted on a pte with its pkey=4.
*/
pkey = vma_pkey(vma);
if (mm)
mmap_read_unlock(mm);
else
vma_end_read(vma);
/*
* If we are in kernel mode, bail out with a SEGV, this will
* be caught by the assembly which will restore the non-volatile
* registers before calling bad_page_fault()
*/
if (!user_mode(regs))
return SIGSEGV;
_exception_pkey(regs, address, pkey);
return 0;
}
static noinline int bad_access(struct pt_regs *regs, unsigned long address,
struct mm_struct *mm, struct vm_area_struct *vma)
{
return __bad_area(regs, address, SEGV_ACCERR, mm, vma);
}
static int do_sigbus(struct pt_regs *regs, unsigned long address,
vm_fault_t fault)
{
if (!user_mode(regs))
return SIGBUS;
current->thread.trap_nr = BUS_ADRERR;
#ifdef CONFIG_MEMORY_FAILURE
if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
unsigned int lsb = 0; /* shutup gcc */
pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
current->comm, current->pid, address);
if (fault & VM_FAULT_HWPOISON_LARGE)
lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
if (fault & VM_FAULT_HWPOISON)
lsb = PAGE_SHIFT;
force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
return 0;
}
#endif
force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
return 0;
}
static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
vm_fault_t fault)
{
/*
* Kernel page fault interrupted by SIGKILL. We have no reason to
* continue processing.
*/
if (fatal_signal_pending(current) && !user_mode(regs))
return SIGKILL;
/* Out of memory */
if (fault & VM_FAULT_OOM) {
/*
* We ran out of memory, or some other thing happened to us that
* made us unable to handle the page fault gracefully.
*/
if (!user_mode(regs))
return SIGSEGV;
pagefault_out_of_memory();
} else {
if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
VM_FAULT_HWPOISON_LARGE))
return do_sigbus(regs, addr, fault);
else if (fault & VM_FAULT_SIGSEGV)
return bad_area_nosemaphore(regs, addr);
else
BUG();
}
return 0;
}
/* Is this a bad kernel fault ? */
static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address, bool is_write)
{
int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
if (is_exec) {
pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
address >= TASK_SIZE ? "exec-protected" : "user",
address,
from_kuid(&init_user_ns, current_uid()));
// Kernel exec fault is always bad
return true;
}
// Kernel fault on kernel address is bad
if (address >= TASK_SIZE)
return true;
// Read/write fault blocked by KUAP is bad, it can never succeed.
if (bad_kuap_fault(regs, address, is_write)) {
pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n",
is_write ? "write" : "read", address,
from_kuid(&init_user_ns, current_uid()));
// Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
if (!search_exception_tables(regs->nip))
return true;
// Read/write fault in a valid region (the exception table search passed
// above), but blocked by KUAP is bad, it can never succeed.
return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read");
}
// What's left? Kernel fault on user and allowed by KUAP in the faulting context.
return false;
}
static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey,
struct vm_area_struct *vma)
{
/*
* Make sure to check the VMA so that we do not perform
* faults just to hit a pkey fault as soon as we fill in a
* page. Only called for current mm, hence foreign == 0
*/
if (!arch_vma_access_permitted(vma, is_write, is_exec, 0))
return true;
return false;
}
static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma)
{
/*
* Allow execution from readable areas if the MMU does not
* provide separate controls over reading and executing.
*
* Note: That code used to not be enabled for 4xx/BookE.
* It is now as I/D cache coherency for these is done at
* set_pte_at() time and I see no reason why the test
* below wouldn't be valid on those processors. This -may-
* break programs compiled with a really old ABI though.
*/
if (is_exec) {
return !(vma->vm_flags & VM_EXEC) &&
(cpu_has_feature(CPU_FTR_NOEXECUTE) ||
!(vma->vm_flags & (VM_READ | VM_WRITE)));
}
if (is_write) {
if (unlikely(!(vma->vm_flags & VM_WRITE)))
return true;
return false;
}
/*
* VM_READ, VM_WRITE and VM_EXEC may imply read permissions, as
* defined in protection_map[]. In that case Read faults can only be
* caused by a PROT_NONE mapping. However a non exec access on a
* VM_EXEC only mapping is invalid anyway, so report it as such.
*/
if (unlikely(!vma_is_accessible(vma)))
return true;
if ((vma->vm_flags & VM_ACCESS_FLAGS) == VM_EXEC)
return true;
/*
* We should ideally do the vma pkey access check here. But in the
* fault path, handle_mm_fault() also does the same check. To avoid
* these multiple checks, we skip it here and handle access error due
* to pkeys later.
*/
return false;
}
#ifdef CONFIG_PPC_SMLPAR
static inline void cmo_account_page_fault(void)
{
if (firmware_has_feature(FW_FEATURE_CMO)) {
u32 page_ins;
preempt_disable();
page_ins = be32_to_cpu(get_lppaca()->page_ins);
page_ins += 1 << PAGE_FACTOR;
get_lppaca()->page_ins = cpu_to_be32(page_ins);
preempt_enable();
}
}
#else
static inline void cmo_account_page_fault(void) { }
#endif /* CONFIG_PPC_SMLPAR */
static void sanity_check_fault(bool is_write, bool is_user,
unsigned long error_code, unsigned long address)
{
/*
* Userspace trying to access kernel address, we get PROTFAULT for that.
*/
if (is_user && address >= TASK_SIZE) {
if ((long)address == -1)
return;
pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
current->comm, current->pid, address,
from_kuid(&init_user_ns, current_uid()));
return;
}
if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
return;
/*
* For hash translation mode, we should never get a
* PROTFAULT. Any update to pte to reduce access will result in us
* removing the hash page table entry, thus resulting in a DSISR_NOHPTE
* fault instead of DSISR_PROTFAULT.
*
* A pte update to relax the access will not result in a hash page table
* entry invalidate and hence can result in DSISR_PROTFAULT.
* ptep_set_access_flags() doesn't do a hpte flush. This is why we have
* the special !is_write in the below conditional.
*
* For platforms that doesn't supports coherent icache and do support
* per page noexec bit, we do setup things such that we do the
* sync between D/I cache via fault. But that is handled via low level
* hash fault code (hash_page_do_lazy_icache()) and we should not reach
* here in such case.
*
* For wrong access that can result in PROTFAULT, the above vma->vm_flags
* check should handle those and hence we should fall to the bad_area
* handling correctly.
*
* For embedded with per page exec support that doesn't support coherent
* icache we do get PROTFAULT and we handle that D/I cache sync in
* set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
* is conditional for server MMU.
*
* For radix, we can get prot fault for autonuma case, because radix
* page table will have them marked noaccess for user.
*/
if (radix_enabled() || is_write)
return;
WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
}
/*
* Define the correct "is_write" bit in error_code based
* on the processor family
*/
#ifdef CONFIG_BOOKE
#define page_fault_is_write(__err) ((__err) & ESR_DST)
#else
#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
#endif
#ifdef CONFIG_BOOKE
#define page_fault_is_bad(__err) (0)
#elif defined(CONFIG_PPC_8xx)
#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G)
#elif defined(CONFIG_PPC64)
static int page_fault_is_bad(unsigned long err)
{
unsigned long flag = DSISR_BAD_FAULT_64S;
/*
* PAPR+ v2.11 ยง 14.15.3.4.1 (unreleased)
* If byte 0, bit 3 of pi-attribute-specifier-type in
* ibm,pi-features property is defined, ignore the DSI error
* which is caused by the paste instruction on the
* suspended NX window.
*/
if (mmu_has_feature(MMU_FTR_NX_DSI))
flag &= ~DSISR_BAD_COPYPASTE;
return err & flag;
}
#else
#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
#endif
/*
* For 600- and 800-family processors, the error_code parameter is DSISR
* for a data fault, SRR1 for an instruction fault.
* For 400-family processors the error_code parameter is ESR for a data fault,
* 0 for an instruction fault.
* For 64-bit processors, the error_code parameter is DSISR for a data access
* fault, SRR1 & 0x08000000 for an instruction access fault.
*
* The return value is 0 if the fault was handled, or the signal
* number if this is a kernel fault that can't be handled here.
*/
static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
unsigned long error_code)
{
struct vm_area_struct * vma;
struct mm_struct *mm = current->mm;
unsigned int flags = FAULT_FLAG_DEFAULT;
int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
int is_user = user_mode(regs);
int is_write = page_fault_is_write(error_code);
vm_fault_t fault, major = 0;
bool kprobe_fault = kprobe_page_fault(regs, 11);
if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
return 0;
if (unlikely(page_fault_is_bad(error_code))) {
if (is_user) {
_exception(SIGBUS, regs, BUS_OBJERR, address);
return 0;
}
return SIGBUS;
}
/* Additional sanity check(s) */
sanity_check_fault(is_write, is_user, error_code, address);
/*
* The kernel should never take an execute fault nor should it
* take a page fault to a kernel address or a page fault to a user
* address outside of dedicated places
*/
if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) {
if (kfence_handle_page_fault(address, is_write, regs))
return 0;
return SIGSEGV;
}
/*
* If we're in an interrupt, have no user context or are running
* in a region with pagefaults disabled then we must not take the fault
*/
if (unlikely(faulthandler_disabled() || !mm)) {
if (is_user)
printk_ratelimited(KERN_ERR "Page fault in user mode"
" with faulthandler_disabled()=%d"
" mm=%p\n",
faulthandler_disabled(), mm);
return bad_area_nosemaphore(regs, address);
}
interrupt_cond_local_irq_enable(regs);
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
/*
* We want to do this outside mmap_lock, because reading code around nip
* can result in fault, which will cause a deadlock when called with
* mmap_lock held
*/
if (is_user)
flags |= FAULT_FLAG_USER;
if (is_write)
flags |= FAULT_FLAG_WRITE;
if (is_exec)
flags |= FAULT_FLAG_INSTRUCTION;
if (!(flags & FAULT_FLAG_USER))
goto lock_mmap;
vma = lock_vma_under_rcu(mm, address);
if (!vma)
goto lock_mmap;
if (unlikely(access_pkey_error(is_write, is_exec,
(error_code & DSISR_KEYFAULT), vma))) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
return bad_access_pkey(regs, address, NULL, vma);
}
if (unlikely(access_error(is_write, is_exec, vma))) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
return bad_access(regs, address, NULL, vma);
}
fault = handle_mm_fault(vma, address, flags | FAULT_FLAG_VMA_LOCK, regs);
if (!(fault & (VM_FAULT_RETRY | VM_FAULT_COMPLETED)))
vma_end_read(vma);
if (!(fault & VM_FAULT_RETRY)) {
count_vm_vma_lock_event(VMA_LOCK_SUCCESS);
goto done;
}
count_vm_vma_lock_event(VMA_LOCK_RETRY);
if (fault & VM_FAULT_MAJOR)
flags |= FAULT_FLAG_TRIED;
if (fault_signal_pending(fault, regs))
return user_mode(regs) ? 0 : SIGBUS;
lock_mmap:
/* When running in the kernel we expect faults to occur only to
* addresses in user space. All other faults represent errors in the
* kernel and should generate an OOPS. Unfortunately, in the case of an
* erroneous fault occurring in a code path which already holds mmap_lock
* we will deadlock attempting to validate the fault against the
* address space. Luckily the kernel only validly references user
* space from well defined areas of code, which are listed in the
* exceptions table. lock_mm_and_find_vma() handles that logic.
*/
retry:
vma = lock_mm_and_find_vma(mm, address, regs);
if (unlikely(!vma))
return bad_area_nosemaphore(regs, address);
if (unlikely(access_pkey_error(is_write, is_exec,
(error_code & DSISR_KEYFAULT), vma)))
return bad_access_pkey(regs, address, mm, vma);
if (unlikely(access_error(is_write, is_exec, vma)))
return bad_access(regs, address, mm, vma);
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
* the fault.
*/
fault = handle_mm_fault(vma, address, flags, regs);
major |= fault & VM_FAULT_MAJOR;
if (fault_signal_pending(fault, regs))
return user_mode(regs) ? 0 : SIGBUS;
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
goto out;
/*
* Handle the retry right now, the mmap_lock has been released in that
* case.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
flags |= FAULT_FLAG_TRIED;
goto retry;
}
mmap_read_unlock(current->mm);
done:
if (unlikely(fault & VM_FAULT_ERROR))
return mm_fault_error(regs, address, fault);
out:
/*
* Major/minor page fault accounting.
*/
if (major)
cmo_account_page_fault();
return 0;
}
NOKPROBE_SYMBOL(___do_page_fault);
static __always_inline void __do_page_fault(struct pt_regs *regs)
{
long err;
err = ___do_page_fault(regs, regs->dar, regs->dsisr);
if (unlikely(err))
bad_page_fault(regs, err);
}
DEFINE_INTERRUPT_HANDLER(do_page_fault)
{
__do_page_fault(regs);
}
#ifdef CONFIG_PPC_BOOK3S_64
/* Same as do_page_fault but interrupt entry has already run in do_hash_fault */
void hash__do_page_fault(struct pt_regs *regs)
{
__do_page_fault(regs);
}
NOKPROBE_SYMBOL(hash__do_page_fault);
#endif
/*
* bad_page_fault is called when we have a bad access from the kernel.
* It is called from the DSI and ISI handlers in head.S and from some
* of the procedures in traps.c.
*/
static void __bad_page_fault(struct pt_regs *regs, int sig)
{
int is_write = page_fault_is_write(regs->dsisr);
const char *msg;
/* kernel has accessed a bad area */
if (regs->dar < PAGE_SIZE)
msg = "Kernel NULL pointer dereference";
else
msg = "Unable to handle kernel data access";
switch (TRAP(regs)) {
case INTERRUPT_DATA_STORAGE:
case INTERRUPT_H_DATA_STORAGE:
pr_alert("BUG: %s on %s at 0x%08lx\n", msg,
is_write ? "write" : "read", regs->dar);
break;
case INTERRUPT_DATA_SEGMENT:
pr_alert("BUG: %s at 0x%08lx\n", msg, regs->dar);
break;
case INTERRUPT_INST_STORAGE:
case INTERRUPT_INST_SEGMENT:
pr_alert("BUG: Unable to handle kernel instruction fetch%s",
regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
break;
case INTERRUPT_ALIGNMENT:
pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
regs->dar);
break;
default:
pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
regs->dar);
break;
}
printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
regs->nip);
if (task_stack_end_corrupted(current))
printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
die("Kernel access of bad area", regs, sig);
}
void bad_page_fault(struct pt_regs *regs, int sig)
{
const struct exception_table_entry *entry;
/* Are we prepared to handle this fault? */
entry = search_exception_tables(instruction_pointer(regs));
if (entry)
instruction_pointer_set(regs, extable_fixup(entry));
else
__bad_page_fault(regs, sig);
}
#ifdef CONFIG_PPC_BOOK3S_64
DEFINE_INTERRUPT_HANDLER(do_bad_page_fault_segv)
{
bad_page_fault(regs, SIGSEGV);
}
/*
* In radix, segment interrupts indicate the EA is not addressable by the
* page table geometry, so they are always sent here.
*
* In hash, this is called if do_slb_fault returns error. Typically it is
* because the EA was outside the region allowed by software.
*/
DEFINE_INTERRUPT_HANDLER(do_bad_segment_interrupt)
{
int err = regs->result;
if (err == -EFAULT) {
if (user_mode(regs))
_exception(SIGSEGV, regs, SEGV_BNDERR, regs->dar);
else
bad_page_fault(regs, SIGSEGV);
} else if (err == -EINVAL) {
unrecoverable_exception(regs);
} else {
BUG();
}
}
#endif
Codebase Browser
linux