Back when set_fs() was a generic API for altering the address limit,
addr_limit_user_check() was a safety measure to prevent userspace being
able to issue syscalls with an unbound limit.
With the the removal of set_fs() as a generic API, the last user of
addr_limit_user_check() was removed in commit:
b5a5a01d8e9a44ec ("arm64: uaccess: remove addr_limit_user_check()")
... as since that commit, no architecture defines TIF_FSCHECK, and hence
addr_limit_user_check() always expands to nothing.
Remove addr_limit_user_check(), updating the comment in
exit_to_user_mode_prepare() to no longer refer to it. At the same time,
the comment is reworded to be a little more generic so as to cover
kmap_assert_nomap() in addition to lockdep_sys_exit().
No functional change.
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230821163526.2319443-1-mark.rutland@arm.com
#endif
/*
- * Called before coming back to user-mode. Returning to user-mode with an
- * address limit different than USER_DS can allow to overwrite kernel memory.
- */
-static inline void addr_limit_user_check(void)
-{
-#ifdef TIF_FSCHECK
- if (!test_thread_flag(TIF_FSCHECK))
- return;
-#endif
-
-#ifdef TIF_FSCHECK
- clear_thread_flag(TIF_FSCHECK);
-#endif
-}
-
-/*
* These syscall function prototypes are kept in the same order as
* include/uapi/asm-generic/unistd.h. Architecture specific entries go below,
* followed by deprecated or obsolete system calls.
arch_exit_to_user_mode_prepare(regs, ti_work);
- /* Ensure that the address limit is intact and no locks are held */
- addr_limit_user_check();
+ /* Ensure that kernel state is sane for a return to userspace */
kmap_assert_nomap();
lockdep_assert_irqs_disabled();
lockdep_sys_exit();