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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:

  b5a5a01d8e ("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
This commit is contained in:
Mark Rutland 2023-08-21 17:35:26 +01:00 committed by Thomas Gleixner
parent 6eaae19807
commit 1dfe3a5a7c
2 changed files with 1 additions and 18 deletions
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16
include/linux/syscalls.h
View File

@ -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,

3
kernel/entry/common.c
View File

@ -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();