[PATCH] vdso: randomize the i386 vDSO by moving it into a vma

Move the i386 VDSO down into a vma and thus randomize it.

Besides the security implications, this feature also helps debuggers, which
can COW a vma-backed VDSO just like a normal DSO and can thus do
single-stepping and other debugging features.

It's good for hypervisors (Xen, VMWare) too, which typically live in the same
high-mapped address space as the VDSO, hence whenever the VDSO is used, they
get lots of guest pagefaults and have to fix such guest accesses up - which
slows things down instead of speeding things up (the primary purpose of the
VDSO).

There's a new CONFIG_COMPAT_VDSO (default=y) option, which provides support
for older glibcs that still rely on a prelinked high-mapped VDSO.  Newer
distributions (using glibc 2.3.3 or later) can turn this option off.  Turning
it off is also recommended for security reasons: attackers cannot use the
predictable high-mapped VDSO page as syscall trampoline anymore.

There is a new vdso=[0|1] boot option as well, and a runtime
/proc/sys/vm/vdso_enabled sysctl switch, that allows the VDSO to be turned
on/off.

(This version of the VDSO-randomization patch also has working ELF
coredumping, the previous patch crashed in the coredumping code.)

This code is a combined work of the exec-shield VDSO randomization
code and Gerd Hoffmann's hypervisor-centric VDSO patch. Rusty Russell
started this patch and i completed it.

[[email protected]: cleanups]
[[email protected]: compile fix]
[[email protected]: compile fix 2]
[[email protected]: compile fix 3]
[[email protected]: revernt MAXMEM change]
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Arjan van de Ven <[email protected]>
Cc: Gerd Hoffmann <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Zachary Amsden <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Jan Beulich <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a929ea197e48..ff1fa87df8d0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1065,5 +1065,7 @@ void drop_slab(void);
 extern int randomize_va_space;
 #endif
 
+const char *arch_vma_name(struct vm_area_struct *vma);
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_MM_H */
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 349ef908a222..bee12a7a0576 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -189,6 +189,7 @@ enum
 	VM_ZONE_RECLAIM_MODE=31, /* reclaim local zone memory before going off node */
 	VM_ZONE_RECLAIM_INTERVAL=32, /* time period to wait after reclaim failure */
 	VM_PANIC_ON_OOM=33,	/* panic at out-of-memory */
+	VM_VDSO_ENABLED=34,	/* map VDSO into new processes? */
 };