um: Implement probe_kernel_read()

UML needs it's own probe_kernel_read() to handle kernel
mode faults correctly.
The implementation uses mincore() on the host side to detect
whether a page is owned by the UML kernel process.

This fixes also a possible crash when sysrq-t is used.
Starting with 3.10 sysrq-t calls probe_kernel_read() to
read details from the kernel workers. As kernel worker are
completely async pointers may turn NULL while reading them.

Cc: <stian@nixia.no>
Cc: <tj@kernel.org>
Cc: <stable@vger.kernel.org> # 3.10.x
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Richard Weinberger 2013-08-17 18:46:00 +02:00
parent 65984ff9d2
commit f75b1b1bed
4 changed files with 78 additions and 1 deletions

View File

@ -200,6 +200,7 @@ extern int os_unmap_memory(void *addr, int len);
extern int os_drop_memory(void *addr, int length);
extern int can_drop_memory(void);
extern void os_flush_stdout(void);
extern int os_mincore(void *addr, unsigned long len);
/* execvp.c */
extern int execvp_noalloc(char *buf, const char *file, char *const argv[]);

View File

@ -13,7 +13,7 @@ clean-files :=
obj-y = config.o exec.o exitcode.o irq.o ksyms.o mem.o \
physmem.o process.o ptrace.o reboot.o sigio.o \
signal.o smp.o syscall.o sysrq.o time.o tlb.o trap.o \
um_arch.o umid.o skas/
um_arch.o umid.o maccess.o skas/
obj-$(CONFIG_BLK_DEV_INITRD) += initrd.o
obj-$(CONFIG_GPROF) += gprof_syms.o

24
arch/um/kernel/maccess.c Normal file
View File

@ -0,0 +1,24 @@
/*
* Copyright (C) 2013 Richard Weinberger <richrd@nod.at>
*
* 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/uaccess.h>
#include <linux/kernel.h>
#include <os.h>
long probe_kernel_read(void *dst, const void *src, size_t size)
{
void *psrc = (void *)rounddown((unsigned long)src, PAGE_SIZE);
if ((unsigned long)src < PAGE_SIZE || size <= 0)
return -EFAULT;
if (os_mincore(psrc, size + src - psrc) <= 0)
return -EFAULT;
return __probe_kernel_read(dst, src, size);
}

View File

@ -4,6 +4,7 @@
*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>
@ -232,6 +233,57 @@ out:
return ok;
}
static int os_page_mincore(void *addr)
{
char vec[2];
int ret;
ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
if (ret < 0) {
if (errno == ENOMEM || errno == EINVAL)
return 0;
else
return -errno;
}
return vec[0] & 1;
}
int os_mincore(void *addr, unsigned long len)
{
char *vec;
int ret, i;
if (len <= UM_KERN_PAGE_SIZE)
return os_page_mincore(addr);
vec = calloc(1, (len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE);
if (!vec)
return -ENOMEM;
ret = mincore(addr, UM_KERN_PAGE_SIZE, vec);
if (ret < 0) {
if (errno == ENOMEM || errno == EINVAL)
ret = 0;
else
ret = -errno;
goto out;
}
for (i = 0; i < ((len + UM_KERN_PAGE_SIZE - 1) / UM_KERN_PAGE_SIZE); i++) {
if (!(vec[i] & 1)) {
ret = 0;
goto out;
}
}
ret = 1;
out:
free(vec);
return ret;
}
void init_new_thread_signals(void)
{
set_handler(SIGSEGV);