linux-kernel - [RFC 6/9] x86/uaccess: Remove tags from the address before checking

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Date:   Fri,  5 Feb 2021 18:16:27 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [RFC 6/9] x86/uaccess: Remove tags from the address before checking

The tags must not be included into check whether it's okay to access the
userspace address.

__chk_range_not_ok() is at the core or access_ok() and it's handly to
strip tags there.

get_user() and put_user() don't use access_ok(), but check access
against TASK_SIZE direcly in assembly. Strip tags, before calling into
the assembly helper.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/include/asm/uaccess.h | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index c9fa7be3df82..ee0a482b2f1f 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -18,6 +18,9 @@
  */
 static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit)
 {
+	/* Remove tags from the address before comparing to the limit */
+	addr = untagged_addr(addr);
+
 	/*
 	 * If we have used "sizeof()" for the size,
 	 * we know it won't overflow the limit (but
@@ -152,7 +155,12 @@ extern int __get_user_bad(void);
  * Return: zero on success, or -EFAULT on error.
  * On error, the variable @x is set to zero.
  */
-#define get_user(x,ptr) ({ might_fault(); do_get_user_call(get_user,x,ptr); })
+#define get_user(x,ptr)							\
+({									\
+	__typeof__(*(ptr)) *__ptr_clean = untagged_ptr(ptr);		\
+	might_fault();							\
+	do_get_user_call(get_user,x,__ptr_clean);			\
+})
 
 /**
  * __get_user - Get a simple variable from user space, with less checking.
@@ -249,7 +257,11 @@ extern void __put_user_nocheck_8(void);
  *
  * Return: zero on success, or -EFAULT on error.
  */
-#define put_user(x, ptr) ({ might_fault(); do_put_user_call(put_user,x,ptr); })
+#define put_user(x, ptr) ({						\
+	__typeof__(*(ptr)) *__ptr_clean = untagged_ptr(ptr);		\
+	might_fault();							\
+	do_put_user_call(put_user,x,__ptr_clean);			\
+})
 
 /**
  * __put_user - Write a simple value into user space, with less checking.
-- 
2.26.2