From e6e5494cb23d1933735ee47cc674ffe1c4afed6f Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Tue, 27 Jun 2006 02:53:50 -0700 Subject: [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. [akpm@osdl.org: cleanups] [akpm@osdl.org: compile fix] [akpm@osdl.org: compile fix 2] [akpm@osdl.org: compile fix 3] [akpm@osdl.org: revernt MAXMEM change] Signed-off-by: Ingo Molnar Signed-off-by: Arjan van de Ven Cc: Gerd Hoffmann Cc: Rusty Russell Cc: Zachary Amsden Cc: Andi Kleen Cc: Jan Beulich Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/vsyscall.lds.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/i386/kernel/vsyscall.lds.S') diff --git a/arch/i386/kernel/vsyscall.lds.S b/arch/i386/kernel/vsyscall.lds.S index 98699ca..e26975f 100644 --- a/arch/i386/kernel/vsyscall.lds.S +++ b/arch/i386/kernel/vsyscall.lds.S @@ -7,7 +7,7 @@ SECTIONS { - . = VSYSCALL_BASE + SIZEOF_HEADERS; + . = VDSO_PRELINK + SIZEOF_HEADERS; .hash : { *(.hash) } :text .dynsym : { *(.dynsym) } @@ -20,7 +20,7 @@ SECTIONS For the layouts to match, we need to skip more than enough space for the dynamic symbol table et al. If this amount is insufficient, ld -shared will barf. Just increase it here. */ - . = VSYSCALL_BASE + 0x400; + . = VDSO_PRELINK + 0x400; .text : { *(.text) } :text =0x90909090 .note : { *(.note.*) } :text :note -- cgit v1.1