// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2000 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
*/
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/sched/debug.h>
#include <asm/current.h>
#include <asm/tlbflush.h>
#include <arch.h>
#include <as-layout.h>
#include <kern_util.h>
#include <os.h>
#include <skas.h>
/*
* Note this is constrained to return 0, -EFAULT, -EACCES, -ENOMEM by
* segv().
*/
int handle_page_fault(unsigned long address, unsigned long ip,
int is_write, int is_user, int *code_out)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
pmd_t *pmd;
pte_t *pte;
int err = -EFAULT;
unsigned int flags = FAULT_FLAG_DEFAULT;
*code_out = SEGV_MAPERR;
/*
* If the fault was with pagefaults disabled, don't take the fault, just
* fail.
*/
if (faulthandler_disabled())
goto out_nosemaphore;
if (is_user)
flags |= FAULT_FLAG_USER;
retry:
mmap_read_lock(mm);
vma = find_vma(mm, address);
if (!vma)
goto out;
if (vma->vm_start <= address)
goto good_area;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto out;
if (is_user && !ARCH_IS_STACKGROW(address))
goto out;
vma = expand_stack(mm, address);
if (!vma)
goto out_nosemaphore;
good_area:
*code_out = SEGV_ACCERR;
if (is_write) {
if (!(vma->vm_flags & VM_WRITE))
goto out;
flags |= FAULT_FLAG_WRITE;
} else {
/* Don't require VM_READ|VM_EXEC for write faults! */
if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
goto out;
}
do {
vm_fault_t fault;
fault = handle_mm_fault(vma, address, flags, NULL);
if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
goto out_nosemaphore;
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
return 0;
if (unlikely(fault & VM_FAULT_ERROR)) {
if (fault & VM_FAULT_OOM) {
goto out_of_memory;
} else if (fault & VM_FAULT_SIGSEGV) {
goto out;
} else if (fault & VM_FAULT_SIGBUS) {
err = -EACCES;
goto out;
}
BUG();
}
if (fault & VM_FAULT_RETRY) {
flags |= FAULT_FLAG_TRIED;
goto retry;
}
pmd = pmd_off(mm, address);
pte = pte_offset_kernel(pmd, address);
} while (!pte_present(*pte));
err = 0;
/*
* The below warning was added in place of
* pte_mkyoung(); if (is_write) pte_mkdirty();
* If it's triggered, we'd see normally a hang here (a clean pte is
* marked read-only to emulate the dirty bit).
* However, the generic code can mark a PTE writable but clean on a
* concurrent read fault, triggering this harmlessly. So comment it out.
*/
#if 0
WARN_ON(!pte_young(*pte) || (is_write && !pte_dirty(*pte)));
#endif
out:
mmap_read_unlock(mm);
out_nosemaphore:
return err;
out_of_memory:
/*
* We ran out of memory, call the OOM killer, and return the userspace
* (which will retry the fault, or kill us if we got oom-killed).
*/
mmap_read_unlock(mm);
if (!is_user)
goto out_nosemaphore;
pagefault_out_of_memory();
return 0;
}
static void show_segv_info(struct uml_pt_regs *regs)
{
struct task_struct *tsk = current;
struct faultinfo *fi = UPT_FAULTINFO(regs);
if (!unhandled_signal(tsk, SIGSEGV))
return;
if (!printk_ratelimit())
return;
printk("%s%s[%d]: segfault at %lx ip %px sp %px error %x",
task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
tsk->comm, task_pid_nr(tsk), FAULT_ADDRESS(*fi),
(void *)UPT_IP(regs), (void *)UPT_SP(regs),
fi->error_code);
print_vma_addr(KERN_CONT " in ", UPT_IP(regs));
printk(KERN_CONT "\n");
}
static void bad_segv(struct faultinfo fi, unsigned long ip)
{
current->thread.arch.faultinfo = fi;
force_sig_fault(SIGSEGV, SEGV_ACCERR, (void __user *) FAULT_ADDRESS(fi));
}
void fatal_sigsegv(void)
{
force_fatal_sig(SIGSEGV);
do_signal(¤t->thread.regs);
/*
* This is to tell gcc that we're not returning - do_signal
* can, in general, return, but in this case, it's not, since
* we just got a fatal SIGSEGV queued.
*/
os_dump_core();
}
/**
* segv_handler() - the SIGSEGV handler
* @sig: the signal number
* @unused_si: the signal info struct; unused in this handler
* @regs: the ptrace register information
*
* The handler first extracts the faultinfo from the UML ptrace regs struct.
* If the userfault did not happen in an UML userspace process, bad_segv is called.
* Otherwise the signal did happen in a cloned userspace process, handle it.
*/
void segv_handler(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
struct faultinfo * fi = UPT_FAULTINFO(regs);
if (UPT_IS_USER(regs) && !SEGV_IS_FIXABLE(fi)) {
show_segv_info(regs);
bad_segv(*fi, UPT_IP(regs));
return;
}
segv(*fi, UPT_IP(regs), UPT_IS_USER(regs), regs);
}
/*
* We give a *copy* of the faultinfo in the regs to segv.
* This must be done, since nesting SEGVs could overwrite
* the info in the regs. A pointer to the info then would
* give us bad data!
*/
unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
struct uml_pt_regs *regs)
{
jmp_buf *catcher;
int si_code;
int err;
int is_write = FAULT_WRITE(fi);
unsigned long address = FAULT_ADDRESS(fi);
if (!is_user && regs)
current->thread.segv_regs = container_of(regs, struct pt_regs, regs);
if (!is_user && init_mm.context.sync_tlb_range_to) {
/*
* Kernel has pending updates from set_ptes that were not
* flushed yet. Syncing them should fix the pagefault (if not
* we'll get here again and panic).
*/
err = um_tlb_sync(&init_mm);
if (err == -ENOMEM)
report_enomem();
if (err)
panic("Failed to sync kernel TLBs: %d", err);
goto out;
}
else if (current->mm == NULL) {
show_regs(container_of(regs, struct pt_regs, regs));
panic("Segfault with no mm");
}
else if (!is_user && address > PAGE_SIZE && address < TASK_SIZE) {
show_regs(container_of(regs, struct pt_regs, regs));
panic("Kernel tried to access user memory at addr 0x%lx, ip 0x%lx",
address, ip);
}
if (SEGV_IS_FIXABLE(&fi))
err = handle_page_fault(address, ip, is_write, is_user,
&si_code);
else {
err = -EFAULT;
/*
* A thread accessed NULL, we get a fault, but CR2 is invalid.
* This code is used in __do_copy_from_user() of TT mode.
* XXX tt mode is gone, so maybe this isn't needed any more
*/
address = 0;
}
catcher = current->thread.fault_catcher;
if (!err)
goto out;
else if (catcher != NULL) {
current->thread.fault_addr = (void *) address;
UML_LONGJMP(catcher, 1);
}
else if (current->thread.fault_addr != NULL)
panic("fault_addr set but no fault catcher");
else if (!is_user && arch_fixup(ip, regs))
goto out;
if (!is_user) {
show_regs(container_of(regs, struct pt_regs, regs));
panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
address, ip);
}
show_segv_info(regs);
if (err == -EACCES) {
current->thread.arch.faultinfo = fi;
force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
} else {
BUG_ON(err != -EFAULT);
current->thread.arch.faultinfo = fi;
force_sig_fault(SIGSEGV, si_code, (void __user *) address);
}
out:
if (regs)
current->thread.segv_regs = NULL;
return 0;
}
void relay_signal(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
int code, err;
if (!UPT_IS_USER(regs)) {
if (sig == SIGBUS)
printk(KERN_ERR "Bus error - the host /dev/shm or /tmp "
"mount likely just ran out of space\n");
panic("Kernel mode signal %d", sig);
}
arch_examine_signal(sig, regs);
/* Is the signal layout for the signal known?
* Signal data must be scrubbed to prevent information leaks.
*/
code = si->si_code;
err = si->si_errno;
if ((err == 0) && (siginfo_layout(sig, code) == SIL_FAULT)) {
struct faultinfo *fi = UPT_FAULTINFO(regs);
current->thread.arch.faultinfo = *fi;
force_sig_fault(sig, code, (void __user *)FAULT_ADDRESS(*fi));
} else {
printk(KERN_ERR "Attempted to relay unknown signal %d (si_code = %d) with errno %d\n",
sig, code, err);
force_sig(sig);
}
}
void bus_handler(int sig, struct siginfo *si, struct uml_pt_regs *regs)
{
if (current->thread.fault_catcher != NULL)
UML_LONGJMP(current->thread.fault_catcher, 1);
else
relay_signal(sig, si, regs);
}
void winch(int sig, struct siginfo *unused_si, struct uml_pt_regs *regs)
{
do_IRQ(WINCH_IRQ, regs);
}
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