linux-kernel - [RFC PATCH v4 25/27] mm/mmap: Prevent Shadow Stack VMA merges

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Message-Id: <20180921150351.20898-26-yu-cheng.yu@intel.com>
Date:   Fri, 21 Sep 2018 08:03:49 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: [RFC PATCH v4 25/27] mm/mmap: Prevent Shadow Stack VMA merges

Function returns could unwind stacks beyond its allocated area.
We do not merge shadow stack areas.

This and VMA guards prevent shadow stack underflow.

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
---
 mm/mmap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index de2d0faa1c61..fa581ced3f56 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1123,6 +1123,12 @@ struct vm_area_struct *vma_merge(struct mm_struct *mm,
 	if (vm_flags & VM_SPECIAL)
 		return NULL;
 
+	/*
+	 * Do not merge shadow stack areas.
+	 */
+	if (vm_flags & VM_SHSTK)
+		return NULL;
+
 	if (prev)
 		next = prev->vm_next;
 	else
-- 
2.17.1