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kernel/arch/powerpc/mm/fault.c

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/*
* PowerPC version
* Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org)
*
* 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 (engebret@ibm.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#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 <asm/firmware.h>
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/tlbflush.h>
#include <asm/siginfo.h>
#include <asm/debug.h>
#include <asm/inst.h>
static inline bool notify_page_fault(struct pt_regs *regs)
{
bool ret = false;
#ifdef CONFIG_KPROBES
/* kprobe_running() needs smp_processor_id() */
if (!user_mode(regs)) {
preempt_disable();
if (kprobe_running() && kprobe_fault_handler(regs, 11))
ret = true;
preempt_enable();
}
#endif /* CONFIG_KPROBES */
if (unlikely(debugger_fault_handler(regs)))
ret = true;
return ret;
}
/*
* Check whether the instruction inst is a store using
* an update addressing form which will update r1.
*/
static bool store_updates_sp(struct ppc_inst inst)
{
/* check for 1 in the rA field */
if (((ppc_inst_val(inst) >> 16) & 0x1f) != 1)
return false;
/* check major opcode */
switch (ppc_inst_primary_opcode(inst)) {
case OP_STWU:
case OP_STBU:
case OP_STHU:
case OP_STFSU:
case OP_STFDU:
return true;
case OP_STD: /* std or stdu */
return (ppc_inst_val(inst) & 3) == 1;
case OP_31:
/* check minor opcode */
switch ((ppc_inst_val(inst) >> 1) & 0x3ff) {
case OP_31_XOP_STDUX:
case OP_31_XOP_STWUX:
case OP_31_XOP_STBUX:
case OP_31_XOP_STHUX:
case OP_31_XOP_STFSUX:
case OP_31_XOP_STFDUX:
return true;
}
}
return false;
}
/*
* 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 = current->mm;
/*
* Something tried to access memory that isn't in our memory map..
* Fix it, but check if it's kernel or user first..
*/
mmap_read_unlock(mm);
return __bad_area_nosemaphore(regs, address, si_code);
}
static noinline int bad_area(struct pt_regs *regs, unsigned long address)
{
return __bad_area(regs, address, SEGV_MAPERR);
}
#ifdef CONFIG_PPC_MEM_KEYS
static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
struct vm_area_struct *vma)
{
struct mm_struct *mm = current->mm;
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);
mmap_read_unlock(mm);
/*
* 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;
}
#endif
static noinline int bad_access(struct pt_regs *regs, unsigned long address)
{
return __bad_area(regs, address, SEGV_ACCERR);
}
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,
current);
return 0;
}
#endif
force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address, current);
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(bool is_exec, unsigned long error_code,
unsigned long address)
{
if (is_exec) {
printk_ratelimited(KERN_CRIT "kernel tried to execute"
" exec-protected page (%lx) -"
"exploit attempt? (uid: %d)\n",
address, from_kuid(&init_user_ns,
current_uid()));
}
return is_exec || (address >= TASK_SIZE);
}
// This comes from 64-bit struct rt_sigframe + __SIGNAL_FRAMESIZE
#define SIGFRAME_MAX_SIZE (4096 + 128)
static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
struct vm_area_struct *vma, unsigned int flags,
bool *must_retry)
{
/*
* N.B. The POWER/Open ABI allows programs to access up to
* 288 bytes below the stack pointer.
* The kernel signal delivery code writes a bit over 4KB
* below the stack pointer (r1) before decrementing it.
* The exec code can write slightly over 640kB to the stack
* before setting the user r1. Thus we allow the stack to
* expand to 1MB without further checks.
*/
if (address + 0x100000 < vma->vm_end) {
struct ppc_inst __user *nip = (struct ppc_inst __user *)regs->nip;
/* get user regs even if this fault is in kernel mode */
struct pt_regs *uregs = current->thread.regs;
if (uregs == NULL)
return true;
/*
* A user-mode access to an address a long way below
* the stack pointer is only valid if the instruction
* is one which would update the stack pointer to the
* address accessed if the instruction completed,
* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
* (or the byte, halfword, float or double forms).
*
* If we don't check this then any write to the area
* between the last mapped region and the stack will
* expand the stack rather than segfaulting.
*/
if (address + SIGFRAME_MAX_SIZE >= uregs->gpr[1])
return false;
if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
access_ok(nip, sizeof(*nip))) {
struct ppc_inst inst;
if (!probe_user_read_inst(&inst, nip))
return !store_updates_sp(inst);
*must_retry = true;
}
return true;
}
return false;
}
#ifdef CONFIG_PPC_MEM_KEYS
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;
}
#endif
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;
}
if (unlikely(!vma_is_accessible(vma)))
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) {
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
*/
#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
#define page_fault_is_write(__err) ((__err) & ESR_DST)
#define page_fault_is_bad(__err) (0)
#else
#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
#if 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 § 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
#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 non-SLB data access fault,
* - SRR1 & 0x08000000 for a non-SLB instruction access fault
* - 0 any SLB 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) == 0x400;
int is_user = user_mode(regs);
int is_write = page_fault_is_write(error_code);
vm_fault_t fault, major = 0;
bool must_retry = false;
if (notify_page_fault(regs))
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.
*/
if (unlikely(!is_user && bad_kernel_fault(is_exec, error_code, address)))
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);
}
/* We restore the interrupt state now */
if (!arch_irq_disabled_regs(regs))
local_irq_enable();
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;
/* 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.
*
* As the vast majority of faults will be valid we will only perform
* the source reference check when there is a possibility of a deadlock.
* Attempt to lock the address space, if we cannot we then validate the
* source. If this is invalid we can skip the address space check,
* thus avoiding the deadlock.
*/
if (unlikely(!mmap_read_trylock(mm))) {
if (!is_user && !search_exception_tables(regs->nip))
return bad_area_nosemaphore(regs, address);
retry:
mmap_read_lock(mm);
} else {
/*
* The above down_read_trylock() might have succeeded in
* which case we'll have missed the might_sleep() from
* down_read():
*/
might_sleep();
}
vma = find_vma(mm, address);
if (unlikely(!vma))
return bad_area(regs, address);
if (likely(vma->vm_start <= address))
goto good_area;
if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
return bad_area(regs, address);
/* The stack is being expanded, check if it's valid */
if (unlikely(bad_stack_expansion(regs, address, vma, flags,
&must_retry))) {
if (!must_retry)
return bad_area(regs, address);
mmap_read_unlock(mm);
if (fault_in_readable((const char __user *)regs->nip,
sizeof(unsigned int)))
return bad_area_nosemaphore(regs, address);
goto retry;
}
/* Try to expand it */
if (unlikely(expand_stack(vma, address)))
return bad_area(regs, address);
good_area:
#ifdef CONFIG_PPC_MEM_KEYS
if (unlikely(access_pkey_error(is_write, is_exec,
(error_code & DSISR_KEYFAULT), vma)))
return bad_access_pkey(regs, address, vma);
#endif /* CONFIG_PPC_MEM_KEYS */
if (unlikely(access_error(is_write, is_exec, vma)))
return bad_access(regs, address);
/*
* 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);
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);
int do_page_fault(struct pt_regs *regs, unsigned long address,
unsigned long error_code)
{
enum ctx_state prev_state = exception_enter();
int rc = __do_page_fault(regs, address, error_code);
exception_exit(prev_state);
return rc;
}
NOKPROBE_SYMBOL(do_page_fault);
/*
* 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.
*/
void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
{
const struct exception_table_entry *entry;
/* Are we prepared to handle this fault? */
if ((entry = search_exception_tables(regs->nip)) != NULL) {
regs->nip = extable_fixup(entry);
return;
}
/* kernel has accessed a bad area */
switch (TRAP(regs)) {
case 0x300:
case 0x380:
case 0xe00:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"data at address 0x%08lx\n", regs->dar);
break;
case 0x400:
case 0x480:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"instruction fetch\n");
break;
case 0x600:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"unaligned access at address 0x%08lx\n", regs->dar);
break;
default:
printk(KERN_ALERT "Unable to handle kernel paging request for "
"unknown fault\n");
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);
}
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