linux-kernel - [tip: timers/core] x86/vdso: Restrict splitting VVAR VMA

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Message-ID: <157894256767.19145.15296635824788335791.tip-bot2@tip-bot2>
Date:   Mon, 13 Jan 2020 19:09:27 -0000
From:   "tip-bot2 for Dmitry Safonov" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andrei Vagin <avagin@...nvz.org>, Dmitry Safonov <dima@...sta.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: timers/core] x86/vdso: Restrict splitting VVAR VMA

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     35825d690265b6433faa2ba47fa7669ea7e125eb
Gitweb:        https://git.kernel.org/tip/35825d690265b6433faa2ba47fa7669ea7e125eb
Author:        Dmitry Safonov <dima@...sta.com>
AuthorDate:    Tue, 12 Nov 2019 01:27:08 
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Mon, 13 Jan 2020 08:10:54 +01:00

x86/vdso: Restrict splitting VVAR VMA

Forbid splitting VVAR VMA resulting in a stricter ABI and reducing the
amount of corner-cases to consider while working further on VDSO time
namespace support.

As the offset from timens to VVAR page is computed compile-time, the pages
in VVAR should stay together and not being partically mremap()'ed.

Co-developed-by: Andrei Vagin <avagin@...nvz.org>
Signed-off-by: Andrei Vagin <avagin@...nvz.org>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/r/20191112012724.250792-20-dima@arista.com

---
 arch/x86/entry/vdso/vma.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
index f593774..76cbe54 100644
--- a/arch/x86/entry/vdso/vma.c
+++ b/arch/x86/entry/vdso/vma.c
@@ -84,6 +84,18 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
 	return 0;
 }
 
+static int vvar_mremap(const struct vm_special_mapping *sm,
+		struct vm_area_struct *new_vma)
+{
+	const struct vdso_image *image = new_vma->vm_mm->context.vdso_image;
+	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
+
+	if (new_size != -image->sym_vvar_start)
+		return -EINVAL;
+
+	return 0;
+}
+
 static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
 		      struct vm_area_struct *vma, struct vm_fault *vmf)
 {
@@ -136,6 +148,7 @@ static const struct vm_special_mapping vdso_mapping = {
 static const struct vm_special_mapping vvar_mapping = {
 	.name = "[vvar]",
 	.fault = vvar_fault,
+	.mremap = vvar_mremap,
 };
 
 /*