2017-04-10 15:18:31

by Thomas Gleixner

Subject: [patch 2/3] x86/vdso: Plug race between mapping and ELF header setup

The vsyscall32 sysctl can racy against a concurrent fork when it switches
from disabled to enabled:

arch_setup_additional_pages()
if (vdso32_enabled)
--> No mapping
sysctl.vsysscall32()
--> vdso32_enabled = true
create_elf_tables()
ARCH_DLINFO_IA32
if (vdso32_enabled) {
--> Add VDSO entry with NULL pointer

Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for
the newly forked process or not.

Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Mathias Krause <[email protected]>
Cc: [email protected]
---
arch/x86/include/asm/elf.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -287,7 +287,7 @@ struct task_struct;

#define ARCH_DLINFO_IA32 \
do { \
- if (vdso32_enabled) { \
+ if (VDSO_CURRENT_BASE) { \
NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \
} \

2017-04-10 15:56:34

by Andy Lutomirski

Subject: Re: [patch 2/3] x86/vdso: Plug race between mapping and ELF header setup

On Mon, Apr 10, 2017 at 8:14 AM, Thomas Gleixner <[email protected]> wrote:
> The vsyscall32 sysctl can racy against a concurrent fork when it switches
> from disabled to enabled:
>
> arch_setup_additional_pages()
> if (vdso32_enabled)
> --> No mapping
> sysctl.vsysscall32()
> --> vdso32_enabled = true
> create_elf_tables()
> ARCH_DLINFO_IA32
> if (vdso32_enabled) {
> --> Add VDSO entry with NULL pointer
>
> Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for
> the newly forked process or not.

Acked-by: Andy Lutomirski <[email protected]>

2017-04-10 17:58:41

by tip-bot for Vasyl Gomonovych

Subject: [tip:x86/urgent] x86/vdso: Plug race between mapping and ELF header setup

Commit-ID: 6fdc6dd90272ce7e75d744f71535cfbd8d77da81
Gitweb: http://git.kernel.org/tip/6fdc6dd90272ce7e75d744f71535cfbd8d77da81
Author: Thomas Gleixner <[email protected]>
AuthorDate: Mon, 10 Apr 2017 17:14:28 +0200
Committer: Thomas Gleixner <[email protected]>
CommitDate: Mon, 10 Apr 2017 18:31:41 +0200

x86/vdso: Plug race between mapping and ELF header setup

The vsyscall32 sysctl can racy against a concurrent fork when it switches
from disabled to enabled:

arch_setup_additional_pages()
if (vdso32_enabled)
--> No mapping
sysctl.vsysscall32()
--> vdso32_enabled = true
create_elf_tables()
ARCH_DLINFO_IA32
if (vdso32_enabled) {
--> Add VDSO entry with NULL pointer

Make ARCH_DLINFO_IA32 check whether the VDSO mapping has been set up for
the newly forked process or not.

Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Mathias Krause <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

---
arch/x86/include/asm/elf.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
index 9d49c18..3762536 100644
--- a/arch/x86/include/asm/elf.h
+++ b/arch/x86/include/asm/elf.h
@@ -287,7 +287,7 @@ struct task_struct;

#define ARCH_DLINFO_IA32 \
do { \
- if (vdso32_enabled) { \
+ if (VDSO_CURRENT_BASE) { \
NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY); \
NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_CURRENT_BASE); \
} \