[PATCH 2/3] UML - Host VDSO fix

From: Jeff Dike
Date: Tue Feb 20 2007 - 12:05:56 EST

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@xxxxxxxxxxx>
arch/um/os-Linux/elf_aux.c | 3 +++
1 file changed, 3 insertions(+)

Index: linux-2.6.17/arch/um/os-Linux/elf_aux.c
--- linux-2.6.17.orig/arch/um/os-Linux/elf_aux.c 2006-06-17 21:49:35.000000000 -0400
+++ linux-2.6.17/arch/um/os-Linux/elf_aux.c 2007-02-20 10:57:52.000000000 -0500
@@ -40,6 +40,9 @@ __init void scan_elf_aux( char **envp)
switch ( auxv->a_type ) {
__kernel_vsyscall = auxv->a_un.a_val;
+ /* See if the page is under TASK_SIZE */
+ if (__kernel_vsyscall < (unsigned long) envp)
+ __kernel_vsyscall = 0;
vsyscall_ehdr = auxv->a_un.a_val;

Work email - jdike at linux dot intel dot com
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