Commit 1dfe3a5a authored by Mark Rutland's avatar Mark Rutland Committed by Thomas Gleixner
Browse files

entry: Remove empty addr_limit_user_check() 



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:

  b5a5a01d ("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: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230821163526.2319443-1-mark.rutland@arm.com
parent 6eaae198

include/linux/syscalls.h

+0 −16
Original line number Diff line number Diff line
@@ -283,22 +283,6 @@ static inline int is_syscall_trace_event(struct trace_event_call *tp_event) 
#define SYSCALL32_DEFINE6 SYSCALL_DEFINE6

#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,

kernel/entry/common.c

+1 −2
Original line number Diff line number Diff line
@@ -205,8 +205,7 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs) 


	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();