2022-05-11 06:24:36

by Kirill A. Shutemov

Subject: [RFCv2 06/10] 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.

Strip tags in access_ok().

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

Signed-off-by: Kirill A. Shutemov <[email protected]>
---
arch/x86/include/asm/uaccess.h | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index f78e2b3501a1..0f5bf7db4ec9 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -40,7 +40,7 @@ static inline bool pagefault_disabled(void);
#define access_ok(addr, size) \
({ \
WARN_ON_IN_IRQ(); \
- likely(__access_ok(addr, size)); \
+ likely(__access_ok(untagged_addr(addr), size)); \
})

#include <asm-generic/access_ok.h>
@@ -125,7 +125,12 @@ 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)) __user *__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.
@@ -222,7 +227,11 @@ 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)) __user *__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.
--
2.35.1

2022-05-12 15:49:01

by David Laight

Subject: RE: [RFCv2 06/10] x86/uaccess: Remove tags from the address before checking

From: Kirill A. Shutemov
> Sent: 11 May 2022 03:28
>
> The tags must not be included into check whether it's okay to access the
> userspace address.
>
> Strip tags in access_ok().

Why?
Just change the test to check the buffer doesn't cross 1u << 63.


David

-
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