linux/arch/um/os-Linux/elf_aux.c
Jeff Dike 14251809b1 [PATCH] uml: host VDSO fix
This fixes a problem seen by a number of people running UML on newer host
kernels.  init would hang with an infinite segfault loop.

It turns out that the host kernel was providing a AT_SYSINFO_EHDR of
0xffffe000, which faked UML into believing that the host VDSO page could be
reused.  However, AT_SYSINFO pointed into the middle of the address space, and
was unmapped as a result.  Because UML was providing AT_SYSINFO_EHDR and
AT_SYSINFO to its own processes, these would branch to nowhere when trying to
use the VDSO.

The fix is to also check the location of AT_SYSINFO when deciding whether to
use the host's VDSO.

Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-01 14:53:38 -08:00

80 lines
2.1 KiB
C

/*
* arch/um/kernel/elf_aux.c
*
* Scan the Elf auxiliary vector provided by the host to extract
* information about vsyscall-page, etc.
*
* Copyright (C) 2004 Fujitsu Siemens Computers GmbH
* Author: Bodo Stroesser (bodo.stroesser@fujitsu-siemens.com)
*/
#include <elf.h>
#include <stddef.h>
#include "init.h"
#include "elf_user.h"
#include "mem_user.h"
#include <kern_constants.h>
/* Use the one from the kernel - the host may miss it, if having old headers. */
#if UM_ELF_CLASS == UM_ELFCLASS32
typedef Elf32_auxv_t elf_auxv_t;
#else
typedef Elf64_auxv_t elf_auxv_t;
#endif
/* These are initialized very early in boot and never changed */
char * elf_aux_platform;
long elf_aux_hwcap;
unsigned long vsyscall_ehdr;
unsigned long vsyscall_end;
unsigned long __kernel_vsyscall;
__init void scan_elf_aux( char **envp)
{
long page_size = 0;
elf_auxv_t * auxv;
while ( *envp++ != NULL) ;
for ( auxv = (elf_auxv_t *)envp; auxv->a_type != AT_NULL; auxv++) {
switch ( auxv->a_type ) {
case AT_SYSINFO:
__kernel_vsyscall = auxv->a_un.a_val;
/* See if the page is under TASK_SIZE */
if (__kernel_vsyscall < (unsigned long) envp)
__kernel_vsyscall = 0;
break;
case AT_SYSINFO_EHDR:
vsyscall_ehdr = auxv->a_un.a_val;
/* See if the page is under TASK_SIZE */
if (vsyscall_ehdr < (unsigned long) envp)
vsyscall_ehdr = 0;
break;
case AT_HWCAP:
elf_aux_hwcap = auxv->a_un.a_val;
break;
case AT_PLATFORM:
/* elf.h removed the pointer elements from
* a_un, so we have to use a_val, which is
* all that's left.
*/
elf_aux_platform =
(char *) (long) auxv->a_un.a_val;
break;
case AT_PAGESZ:
page_size = auxv->a_un.a_val;
break;
}
}
if ( ! __kernel_vsyscall || ! vsyscall_ehdr ||
! elf_aux_hwcap || ! elf_aux_platform ||
! page_size || (vsyscall_ehdr % page_size) ) {
__kernel_vsyscall = 0;
vsyscall_ehdr = 0;
elf_aux_hwcap = 0;
elf_aux_platform = "i586";
}
else {
vsyscall_end = vsyscall_ehdr + page_size;
}
}