fully honor vdso_enabled [i386, sh; x86_64?]

John Reiser
2007-02-22T20:38:41Z

Architectures such as i386, sh, x86_64 have a flag /proc/sys/vm/vdso_enabled
to choose whether the kernel should setup a process to use vdso after execve().
Informing the user code via AT_SYSINFO* is controlled by macro ARCH_DLINFO in
fs/binfmt_elf.c and include/asm-$ARCH/elf.h, but the vdso page is established
always via arch_setup_additonal_pages() called from load_elf_binary().
If vdso_enabled is off, then current code wastes kernel time during execve()
and fragments the address space unnecessarily.

This patch changes arch_setup_additonal_pages() to honor vdso_enabled.
For i386 it also allows the option of a fixed addresss to avoid
fragmenting the address space. Compiles and runs on i386.
x86_64 [IA32 support] and sh maintainers also please comment.

For some related history, including interaction with exec-shield, see:
http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=229304
and also 207020 and 162797.

Signed-off-by: John Reiser <jreiser@BitWagon.com>

diff --git a/arch/i386/kernel/sysenter.c b/arch/i386/kernel/sysenter.c
index 13ca54a..f8c4d76 100644
--- a/arch/i386/kernel/sysenter.c
+++ b/arch/i386/kernel/sysenter.c
@@ -22,6 +22,8 @@
#include <asm/msr.h>
#include <asm/pgtable.h>
#include <asm/unistd.h>
+#include <asm/a.out.h>
+#include <asm/mman.h>

/*
* Should the kernel map a VDSO page into processes and pass its
@@ -105,10 +107,25 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
{
struct mm_struct *mm = current->mm;
unsigned long addr;
+ unsigned long flags;
int ret;

+ switch (vdso_enabled) {
+ case 0: /* none */
+ return 0;
+ default:
+ case 1: /* vdso in random available page */
+ addr = 0ul;
+ flags = 0ul;
+ break;
+ case 2: /* out of user's way */
+ addr = STACK_TOP;
+ flags = MAP_FIXED;
+ break;
+ }
+
down_write(&mm->mmap_sem);
- addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+ addr = get_unmapped_area(NULL, addr, PAGE_SIZE, 0, flags);
if (IS_ERR_VALUE(addr)) {
ret = addr;
goto up_fail;
diff --git a/arch/sh/kernel/vsyscall/vsyscall.c b/arch/sh/kernel/vsyscall/vsyscall.c
index 7b0f66f..2b789fb 100644
--- a/arch/sh/kernel/vsyscall/vsyscall.c
+++ b/arch/sh/kernel/vsyscall/vsyscall.c
@@ -64,6 +64,9 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
unsigned long addr;
int ret;

+ if (!vdso_enabled)
+ return 0;
+
down_write(&mm->mmap_sem);
addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
if (IS_ERR_VALUE(addr)) {
diff --git a/include/asm-i386/a.out.h b/include/asm-i386/a.out.h
index ab17bb8..9894f73 100644
--- a/include/asm-i386/a.out.h
+++ b/include/asm-i386/a.out.h
@@ -19,7 +19,7 @@ struct exec

#ifdef __KERNEL__

-#define STACK_TOP TASK_SIZE
+#define STACK_TOP (TASK_SIZE - PAGE_SIZE) /* 1 page optional for vdso */

#endif

--