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Commit f75b1b1b authored by Richard Weinberger's avatar Richard Weinberger
Browse files

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: default avatarRichard Weinberger <richard@nod.at>
parent 65984ff9

arch/um/include/shared/os.h

+1 −0
Original line number Diff line number Diff line
@@ -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[]);

arch/um/kernel/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

arch/um/kernel/maccess.c

0 → 100644
+24 −0
Original line number Diff line number Diff line 
/*

 * 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);

}

arch/um/os-Linux/process.c

+52 −0
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
 */



#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <errno.h>

#include <signal.h>
@@ -232,6 +233,57 @@ int __init can_drop_memory(void) 
	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);