[PATCH 0/2] x86/vdso: small fixups for map_vdso

[PATCH 0/2] x86/vdso: small fixups for map_vdso

[Dmitry Safonov]

The first one is a fixup for arch_prctl constants uapi visability,
the second is code simplification.

Dmitry Safonov (2):
  x86/prctl/uapi: remove ifdef for CHECKPOINT_RESTORE
  x86/vdso: set vdso pointer only after success

 arch/x86/entry/vdso/vma.c         | 10 +++-------
 arch/x86/include/uapi/asm/prctl.h |  8 +++-----
 2 files changed, 6 insertions(+), 12 deletions(-)

-- 
2.10.1

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[PATCH 1/2] x86/prctl/uapi: remove ifdef for CHECKPOINT_RESTORE

[Dmitry Safonov]

As userspace knows nothing about kernel config, this ifdefs
will make prctl constants invisible to userspace.
Let it be clean'n'simple: remove ifdefs.
If kernel has CONFIG_CHECKPOINT_RESTORE disabled, sys_prctl()
will return -EINVAL for those prctls.

Fixes: 2eefd8789698 ("x86/arch_prctl/vdso: Add ARCH_MAP_VDSO_*")
Cc: 0x7f454c46@gmail.com
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Paul Bolle <pebolle@tiscali.nl>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: oleg@redhat.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-mm@kvack.org
Cc: x86@kernel.org
Reported-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
---
 arch/x86/include/uapi/asm/prctl.h | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index ae135de547f5..835aa51c7f6e 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -6,10 +6,8 @@
 #define ARCH_GET_FS 0x1003
 #define ARCH_GET_GS 0x1004
 
-#ifdef CONFIG_CHECKPOINT_RESTORE
-# define ARCH_MAP_VDSO_X32	0x2001
-# define ARCH_MAP_VDSO_32	0x2002
-# define ARCH_MAP_VDSO_64	0x2003
-#endif
+#define ARCH_MAP_VDSO_X32	0x2001
+#define ARCH_MAP_VDSO_32	0x2002
+#define ARCH_MAP_VDSO_64	0x2003
 
 #endif /* _ASM_X86_PRCTL_H */
-- 
2.10.1

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[PATCH 2/2] x86/vdso: set vdso pointer only after success

[Dmitry Safonov]

Those pointers were initialized before call to _install_special_mapping
after the commit f7b6eb3fa072 ("x86: Set context.vdso before installing
the mapping"). This is not required anymore as special mappings have
their vma name and don't use arch_vma_name() after commit a62c34bd2a8a
("x86, mm: Improve _install_special_mapping and fix x86 vdso naming").
So, this way to init looks less entangled.
I even belive, we can remove null initializers:
- on failure load_elf_binary() will not start a new thread;
- arch_prctl will have the same pointers as before syscall.

Cc: 0x7f454c46@gmail.com
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: oleg@redhat.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-mm@kvack.org
Cc: x86@kernel.org
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
---
 arch/x86/entry/vdso/vma.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index 23c881caabd1..e739002427ed 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -161,8 +161,6 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
 	}
 
 	text_start = addr - image->sym_vvar_start;
-	current->mm->context.vdso = (void __user *)text_start;
-	current->mm->context.vdso_image = image;
 
 	/*
 	 * MAYWRITE to allow gdb to COW and set breakpoints
@@ -189,14 +187,12 @@ static int map_vdso(const struct vdso_image *image, unsigned long addr)
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
 		do_munmap(mm, text_start, image->size);
+	} else {
+		current->mm->context.vdso = (void __user *)text_start;
+		current->mm->context.vdso_image = image;
 	}
 
 up_fail:
-	if (ret) {
-		current->mm->context.vdso = NULL;
-		current->mm->context.vdso_image = NULL;
-	}
-
 	up_write(&mm->mmap_sem);
 	return ret;
 }
-- 
2.10.1

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Re: [PATCH 2/2] x86/vdso: set vdso pointer only after success

[Andy Lutomirski]

On Thu, Oct 27, 2016 at 7:15 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> Those pointers were initialized before call to _install_special_mapping
> after the commit f7b6eb3fa072 ("x86: Set context.vdso before installing
> the mapping"). This is not required anymore as special mappings have
> their vma name and don't use arch_vma_name() after commit a62c34bd2a8a
> ("x86, mm: Improve _install_special_mapping and fix x86 vdso naming").
> So, this way to init looks less entangled.
> I even belive, we can remove null initializers:
> - on failure load_elf_binary() will not start a new thread;
> - arch_prctl will have the same pointers as before syscall.

Acked-by: Andy Lutomirski <luto@kernel.org>

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