[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>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/um/os-Linux/elf_aux.c b/arch/um/os-Linux/elf_aux.c
index 3a8d7e3aae0a..608784d4ec57 100644
--- a/arch/um/os-Linux/elf_aux.c
+++ b/arch/um/os-Linux/elf_aux.c
@@ -39,6 +39,9 @@ __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;