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

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Date:   Mon, 10 Apr 2017 09:34:32 -0700
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        minipli@...glemail.com, hpa@...or.com, luto@...capital.net,
        tglx@...utronix.de, mingo@...nel.org
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 <tglx@...utronix.de>
AuthorDate: Mon, 10 Apr 2017 17:14:28 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
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 <tglx@...utronix.de>
Acked-by: Andy Lutomirski <luto@...capital.net>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Mathias Krause <minipli@...glemail.com>
Cc: stable@...r.kernel.org
Link: http://lkml.kernel.org/r/20170410151723.602367196@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 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);	\
 	}								\