linux-kernel - [RFC PATCH v2 3/6] arm64: untag user addresses in copy_from

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Message-Id: <22d41e0e1439ed0d13b2a2ca4b7c8317131f7ea9.1522169685.git.andreyknvl@google.com>
Date:   Tue, 27 Mar 2018 18:57:39 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Jonathan Corbet <corbet@....net>,
        Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        James Morse <james.morse@....com>,
        Kees Cook <keescook@...omium.org>,
        Bart Van Assche <bart.vanassche@....com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>
Subject: [RFC PATCH v2 3/6] arm64: untag user addresses in copy_from_user and others

copy_from_user (and a few other similar functions) are used to copy data
from user memory into the kernel memory or vice versa. Since a user can
provided a tagged pointer to one of the syscalls that use copy_from_user,
we need to correctly handle such pointers.

Do this by untagging user pointers in access_ok and in __uaccess_mask_ptr.

Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 arch/arm64/include/asm/uaccess.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 2d6451cbaa86..24a221678fe3 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -105,7 +105,8 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
 #define untagged_addr(addr)		\
 	((__typeof__(addr))sign_extend64((__u64)(addr), 55))
 
-#define access_ok(type, addr, size)	__range_ok(addr, size)
+#define access_ok(type, addr, size)	\
+	__range_ok(untagged_addr(addr), size)
 #define user_addr_max			get_fs
 
 #define _ASM_EXTABLE(from, to)						\
@@ -238,12 +239,15 @@ static inline void uaccess_enable_not_uao(void)
 /*
  * Sanitise a uaccess pointer such that it becomes NULL if above the
  * current addr_limit.
+ * Also untag user pointers that have the top byte tag set.
  */
 #define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
 static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
 {
 	void __user *safe_ptr;
 
+	ptr = untagged_addr(ptr);
+
 	asm volatile(
 	"	bics	xzr, %1, %2\n"
 	"	csel	%0, %1, xzr, eq\n"
-- 
2.17.0.rc0.231.g781580f067-goog