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@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/um/os-Linux/elf_aux.c b/arch/um/os-Linux/elf_aux.c
index 5a99dd3fbed0477bb7443eba1324e70f0dc4bcf4..13c6cb56e315d83a36975f0837cc9f162752fdfd 100644 (file)
--- a/arch/um/os-Linux/elf_aux.c
+++ b/arch/um/os-Linux/elf_aux.c
@@ -40,6 +40,9 @@ __init void scan_elf_aux( char **envp)
                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;