linux-kernel - [PATCH v15 02/17] arm64: untag user pointers in access_ok and __uaccess_mask

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Message-Id: <02e1242715cc1bf23a139e5e8152fb4feaa4b41d.1557160186.git.andreyknvl@google.com>
Date:   Mon,  6 May 2019 18:30:48 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-rdma@...r.kernel.org,
        linux-media@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Felix Kuehling <Felix.Kuehling@....com>,
        Alexander Deucher <Alexander.Deucher@....com>,
        Christian Koenig <Christian.Koenig@....com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        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>,
        Robin Murphy <robin.murphy@....com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Dave Martin <Dave.Martin@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: [PATCH v15 02/17] arm64: untag user pointers in access_ok and __uaccess_mask_ptr

This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.

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,
before performing access validity checks.

Note, that this patch only temporarily untags the pointers to perform the
checks, but then passes them as is into the kernel internals.

Reviewed-by: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
---
 arch/arm64/include/asm/uaccess.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index e5d5f31c6d36..9164ecb5feca 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -94,7 +94,7 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
 	return ret;
 }
 
-#define access_ok(addr, size)	__range_ok(addr, size)
+#define access_ok(addr, size)	__range_ok(untagged_addr(addr), size)
 #define user_addr_max			get_fs
 
 #define _ASM_EXTABLE(from, to)						\
@@ -226,7 +226,8 @@ static inline void uaccess_enable_not_uao(void)
 
 /*
  * Sanitise a uaccess pointer such that it becomes NULL if above the
- * current addr_limit.
+ * current addr_limit. In case the pointer is tagged (has the top byte set),
+ * untag the pointer before checking.
  */
 #define uaccess_mask_ptr(ptr) (__typeof__(ptr))__uaccess_mask_ptr(ptr)
 static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
@@ -234,10 +235,11 @@ static inline void __user *__uaccess_mask_ptr(const void __user *ptr)
 	void __user *safe_ptr;
 
 	asm volatile(
-	"	bics	xzr, %1, %2\n"
+	"	bics	xzr, %3, %2\n"
 	"	csel	%0, %1, xzr, eq\n"
 	: "=&r" (safe_ptr)
-	: "r" (ptr), "r" (current_thread_info()->addr_limit)
+	: "r" (ptr), "r" (current_thread_info()->addr_limit),
+	  "r" (untagged_addr(ptr))
 	: "cc");
 
 	csdb();
-- 
2.21.0.1020.gf2820cf01a-goog