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arm64: untag user pointers in access_ok and __uaccess_mask_ptr 

This patch is a part of a series that extends 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: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
[will: Add __force to casting in untagged_addr() to kill sparse warning]
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Andrey Konovalov 2019-07-23 19:58:38 +02:00 committed by Will Deacon
parent e21a712a96
commit 2b835e24b5
2 changed files with 8 additions and 4 deletions
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2
arch/arm64/include/asm/memory.h
View File

@ -201,7 +201,7 @@ extern u64 vabits_user;
* pass on to access_ok(), for instance.
*/
#define untagged_addr(addr) \
((__typeof__(addr))sign_extend64((u64)(addr), 55))
((__typeof__(addr))sign_extend64((__force u64)(addr), 55))
#ifdef CONFIG_KASAN_SW_TAGS
#define __tag_shifted(tag) ((u64)(tag) << 56)

10
arch/arm64/include/asm/uaccess.h
View File

@ -62,6 +62,8 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
{
unsigned long ret, limit = current_thread_info()->addr_limit;
addr = untagged_addr(addr);
__chk_user_ptr(addr);
asm volatile(
// A + B <= C + 1 for all A,B,C, in four easy steps:
@ -215,7 +217,8 @@ 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)
@ -223,10 +226,11 @@ 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();