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[PATCH] uml: more carefully test whether we are in a system call

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For security reasons, UML in is_syscall() needs to have access to code in
vsyscall-page.  The current implementation grants this access by explicitly
allowing access to vsyscall in access_ok_skas().  With this change,
copy_from_user() may be used to read the code.  Ptrace access to vsyscall-page
for debugging already was implemented in get_user_pages() by mainline.  In
i386, copy_from_user can't access vsyscall-page, but returns EFAULT.

To make UML behave as i386 does, I changed is_syscall to use
access_process_vm(current) to read the code from vsyscall-page.  This doesn't
hurt security, but simplifies the code and prepares implementation of
stub-vmas.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Bodo Stroesser 2006-03-27 01:14:34 -08:00 committed by Linus Torvalds
parent f206aabb03
commit 81efcd3300
2 changed files with 33 additions and 4 deletions
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15
arch/um/sys-i386/ptrace.c
View File

@ -6,6 +6,7 @@
#include <linux/config.h>
#include <linux/compiler.h>
#include "linux/sched.h"
#include "linux/mm.h"
#include "asm/elf.h"
#include "asm/ptrace.h"
#include "asm/uaccess.h"
@ -26,9 +27,17 @@ int is_syscall(unsigned long addr)
n = copy_from_user(&instr, (void __user *) addr, sizeof(instr));
if(n){
printk("is_syscall : failed to read instruction from 0x%lx\n",
addr);
return(0);
/* access_process_vm() grants access to vsyscall and stub,
* while copy_from_user doesn't. Maybe access_process_vm is
* slow, but that doesn't matter, since it will be called only
* in case of singlestepping, if copy_from_user failed.
*/
n = access_process_vm(current, addr, &instr, sizeof(instr), 0);
if(n != sizeof(instr)) {
printk("is_syscall : failed to read instruction from "
"0x%lx\n", addr);
return(1);
}
}
/* int 0x80 or sysenter */
return((instr == 0x80cd) || (instr == 0x340f));

22
arch/um/sys-x86_64/ptrace.c
View File

@ -8,6 +8,7 @@
#include <asm/ptrace.h>
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <asm/uaccess.h>
#include <asm/elf.h>
@ -136,9 +137,28 @@ void arch_switch(void)
*/
}
/* XXX Mostly copied from sys-i386 */
int is_syscall(unsigned long addr)
{
panic("is_syscall");
unsigned short instr;
int n;
n = copy_from_user(&instr, (void __user *) addr, sizeof(instr));
if(n){
/* access_process_vm() grants access to vsyscall and stub,
* while copy_from_user doesn't. Maybe access_process_vm is
* slow, but that doesn't matter, since it will be called only
* in case of singlestepping, if copy_from_user failed.
*/
n = access_process_vm(current, addr, &instr, sizeof(instr), 0);
if(n != sizeof(instr)) {
printk("is_syscall : failed to read instruction from "
"0x%lx\n", addr);
return(1);
}
}
/* sysenter */
return(instr == 0x050f);
}
int dump_fpu(struct pt_regs *regs, elf_fpregset_t *fpu )