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kernel-fxtec-pro1x/arch/avr32/mm/fault.c
Linus Torvalds 33692f2759 vm: add VM_FAULT_SIGSEGV handling support 
The core VM already knows about VM_FAULT_SIGBUS, but cannot return a
"you should SIGSEGV" error, because the SIGSEGV case was generally
handled by the caller - usually the architecture fault handler.

That results in lots of duplication - all the architecture fault
handlers end up doing very similar "look up vma, check permissions, do
retries etc" - but it generally works.  However, there are cases where
the VM actually wants to SIGSEGV, and applications _expect_ SIGSEGV.

In particular, when accessing the stack guard page, libsigsegv expects a
SIGSEGV.  And it usually got one, because the stack growth is handled by
that duplicated architecture fault handler.

However, when the generic VM layer started propagating the error return
from the stack expansion in commit fee7e49d45 ("mm: propagate error
from stack expansion even for guard page"), that now exposed the
existing VM_FAULT_SIGBUS result to user space.  And user space really
expected SIGSEGV, not SIGBUS.

To fix that case, we need to add a VM_FAULT_SIGSEGV, and teach all those
duplicate architecture fault handlers about it.  They all already have
the code to handle SIGSEGV, so it's about just tying that new return
value to the existing code, but it's all a bit annoying.

This is the mindless minimal patch to do this.  A more extensive patch
would be to try to gather up the mostly shared fault handling logic into
one generic helper routine, and long-term we really should do that
cleanup.

Just from this patch, you can generally see that most architectures just
copied (directly or indirectly) the old x86 way of doing things, but in
the meantime that original x86 model has been improved to hold the VM
semaphore for shorter times etc and to handle VM_FAULT_RETRY and other
"newer" things, so it would be a good idea to bring all those
improvements to the generic case and teach other architectures about
them too.

Reported-and-tested-by: Takashi Iwai <tiwai@suse.de>
Tested-by: Jan Engelhardt <jengelh@inai.de>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # "s390 still compiles and boots"
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-01-29 10:51:32 -08:00

268 lines
6.2 KiB
C
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/*
* Copyright (C) 2004-2006 Atmel Corporation
*
* Based on linux/arch/sh/mm/fault.c:
* Copyright (C) 1999 Niibe Yutaka
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/pagemap.h>
#include <linux/kdebug.h>
#include <linux/kprobes.h>
#include <asm/mmu_context.h>
#include <asm/sysreg.h>
#include <asm/tlb.h>
#include <asm/uaccess.h>
#ifdef CONFIG_KPROBES
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
int ret = 0;
if (!user_mode(regs)) {
if (kprobe_running() && kprobe_fault_handler(regs, trap))
ret = 1;
}
return ret;
}
#else
static inline int notify_page_fault(struct pt_regs *regs, int trap)
{
return 0;
}
#endif
int exception_trace = 1;
/*
* This routine handles page faults. It determines the address and the
* problem, and then passes it off to one of the appropriate routines.
*
* ecr is the Exception Cause Register. Possible values are:
* 6: Protection fault (instruction access)
* 15: Protection fault (read access)
* 16: Protection fault (write access)
* 20: Page not found (instruction access)
* 24: Page not found (read access)
* 28: Page not found (write access)
*/
asmlinkage void do_page_fault(unsigned long ecr, struct pt_regs *regs)
{
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct *vma;
const struct exception_table_entry *fixup;
unsigned long address;
unsigned long page;
long signr;
int code;
int fault;
unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
if (notify_page_fault(regs, ecr))
return;
address = sysreg_read(TLBEAR);
tsk = current;
mm = tsk->mm;
signr = SIGSEGV;
code = SEGV_MAPERR;
/*
* If we're in an interrupt or have no user context, we must
* not take the fault...
*/
if (in_atomic() || !mm || regs->sr & SYSREG_BIT(GM))
goto no_context;
local_irq_enable();
if (user_mode(regs))
flags |= FAULT_FLAG_USER;
retry:
down_read(&mm->mmap_sem);
vma = find_vma(mm, address);
if (!vma)
goto bad_area;
if (vma->vm_start <= address)
goto good_area;
if (!(vma->vm_flags & VM_GROWSDOWN))
goto bad_area;
if (expand_stack(vma, address))
goto bad_area;
/*
* Ok, we have a good vm_area for this memory access, so we
* can handle it...
*/
good_area:
code = SEGV_ACCERR;
switch (ecr) {
case ECR_PROTECTION_X:
case ECR_TLB_MISS_X:
if (!(vma->vm_flags & VM_EXEC))
goto bad_area;
break;
case ECR_PROTECTION_R:
case ECR_TLB_MISS_R:
if (!(vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)))
goto bad_area;
break;
case ECR_PROTECTION_W:
case ECR_TLB_MISS_W:
if (!(vma->vm_flags & VM_WRITE))
goto bad_area;
flags |= FAULT_FLAG_WRITE;
break;
default:
panic("Unhandled case %lu in do_page_fault!", ecr);
}
/*
* 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(mm, vma, address, flags);
if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current))
return;
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 (flags & FAULT_FLAG_ALLOW_RETRY) {
if (fault & VM_FAULT_MAJOR)
tsk->maj_flt++;
else
tsk->min_flt++;
if (fault & VM_FAULT_RETRY) {
flags &= ~FAULT_FLAG_ALLOW_RETRY;
flags |= FAULT_FLAG_TRIED;
/*
* No need to up_read(&mm->mmap_sem) as we would have
* already released it in __lock_page_or_retry() in
* mm/filemap.c.
*/
goto retry;
}
}
up_read(&mm->mmap_sem);
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:
up_read(&mm->mmap_sem);
if (user_mode(regs)) {
if (exception_trace && printk_ratelimit())
printk("%s%s[%d]: segfault at %08lx pc %08lx "
"sp %08lx ecr %lu\n",
is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
tsk->comm, tsk->pid, address, regs->pc,
regs->sp, ecr);
_exception(SIGSEGV, regs, code, address);
return;
}
no_context:
/* Are we prepared to handle this kernel fault? */
fixup = search_exception_tables(regs->pc);
if (fixup) {
regs->pc = fixup->fixup;
return;
}
/*
* Oops. The kernel tried to access some bad page. We'll have
* to terminate things with extreme prejudice.
*/
if (address < PAGE_SIZE)
printk(KERN_ALERT
"Unable to handle kernel NULL pointer dereference");
else
printk(KERN_ALERT
"Unable to handle kernel paging request");
printk(" at virtual address %08lx\n", address);
page = sysreg_read(PTBR);
printk(KERN_ALERT "ptbr = %08lx", page);
if (address >= TASK_SIZE)
page = (unsigned long)swapper_pg_dir;
if (page) {
page = ((unsigned long *)page)[address >> 22];
printk(" pgd = %08lx", page);
if (page & _PAGE_PRESENT) {
page &= PAGE_MASK;
address &= 0x003ff000;
page = ((unsigned long *)__va(page))[address >> PAGE_SHIFT];
printk(" pte = %08lx", page);
}
}
printk("\n");
die("Kernel access of bad area", regs, signr);
return;
/*
* 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:
up_read(&mm->mmap_sem);
if (!user_mode(regs))
goto no_context;
pagefault_out_of_memory();
return;
do_sigbus:
up_read(&mm->mmap_sem);
/* Kernel mode? Handle exceptions or die */
signr = SIGBUS;
code = BUS_ADRERR;
if (!user_mode(regs))
goto no_context;
if (exception_trace)
printk("%s%s[%d]: bus error at %08lx pc %08lx "
"sp %08lx ecr %lu\n",
is_global_init(tsk) ? KERN_EMERG : KERN_INFO,
tsk->comm, tsk->pid, address, regs->pc,
regs->sp, ecr);
_exception(SIGBUS, regs, BUS_ADRERR, address);
}
asmlinkage void do_bus_error(unsigned long addr, int write_access,
struct pt_regs *regs)
{
printk(KERN_ALERT
"Bus error at physical address 0x%08lx (%s access)\n",
addr, write_access ? "write" : "read");
printk(KERN_INFO "DTLB dump:\n");
dump_dtlb();
die("Bus Error", regs, SIGKILL);
}
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