Re: [patch 09/18] entry: Remove syscall_enter_from_user_mode()

[Radu Rendec <radu@rendec.net>]

On Tue, 2026-07-07 at 21:06 +0200, Thomas Gleixner wrote:
> All architecture use either:
> 
>     nr = enter_from_user_mode_randomize_stack(regs, nr);

You probably mean syscall_enter_from_user_mode_randomize_stack.

> 
> or
> 
>     enter_from_user_mode_randomize_stack(regs);
>     nr = syscall_enter_from_user_mode_work(regs, nr);
> 
> Remove the now unused function.
> 
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> ---
>  Documentation/core-api/entry.rst |   17 +++++++++-------
>  include/linux/entry-common.h     |   40 +++------------------------------------
>  include/linux/irq-entry-common.h |    6 ++---
>  3 files changed, 17 insertions(+), 46 deletions(-)
> 
> --- a/Documentation/core-api/entry.rst
> +++ b/Documentation/core-api/entry.rst
> @@ -68,7 +68,7 @@ low-level C code must not be instrumente
>    noinstr void syscall(struct pt_regs *regs, int nr)
>    {
>  	arch_syscall_enter(regs);
> -	nr = syscall_enter_from_user_mode(regs, nr);
> +	nr = syscall_enter_from_user_mode_randomize_stack(regs, nr);
>  
>  	instrumentation_begin();
>  	if (!invoke_syscall(regs, nr) && nr != -1)
> @@ -78,12 +78,14 @@ low-level C code must not be instrumente
>  	syscall_exit_to_user_mode(regs);
>    }
>  
> -syscall_enter_from_user_mode() first invokes enter_from_user_mode() which
> -establishes state in the following order:
> +syscall_enter_from_user_mode_randomize_stack() first invokes
> +enter_from_user_mode_randomize_stack() which establishes state in the
> +following order:
>  
>    * Lockdep
>    * RCU / Context tracking
>    * Tracing
> +  * Apply stack randomization
>  
>  and then invokes the various entry work functions like ptrace, seccomp, audit,
>  syscall tracing, etc. After all that is done, the instrumentable invoke_syscall
> @@ -99,10 +101,11 @@ that it invokes exit_to_user_mode() whic
>    * RCU / Context tracking
>    * Lockdep
>  
> -syscall_enter_from_user_mode() and syscall_exit_to_user_mode() are also
> -available as fine grained subfunctions in cases where the architecture code
> -has to do extra work between the various steps. In such cases it has to
> -ensure that enter_from_user_mode() is called first on entry and
> +syscall_enter_from_user_mode_randomize_stack() and
> +syscall_exit_to_user_mode() are also available as fine grained subfunctions
> +in cases where the architecture code has to do extra work between the
> +various steps. In such cases it has to ensure that
> +enter_from_user_mode_randomize_stack() is called first on entry and
>  exit_to_user_mode() is called last on exit.
>  
>  Do not nest syscalls. Nested syscalls will cause RCU and/or context tracking
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -19,7 +19,7 @@
>  #endif
>  
>  /*
> - * SYSCALL_WORK flags handled in syscall_enter_from_user_mode()
> + * SYSCALL_WORK flags handled in syscall_enter_from_user_mode_work()
>   */
>  #define SYSCALL_WORK_ENTER	(SYSCALL_WORK_SECCOMP |			\
>  				 SYSCALL_WORK_SYSCALL_TRACEPOINT |	\
> @@ -205,42 +205,10 @@ do {									\
>  	_ret;								\
>  })
>  
> -/**
> - * syscall_enter_from_user_mode - Establish state and check and handle work
> - *				  before invoking a syscall
> - * @regs:	Pointer to currents pt_regs
> - * @syscall:	The syscall number
> - *
> - * Invoked from architecture specific syscall entry code with interrupts
> - * disabled. The calling code has to be non-instrumentable. When the
> - * function returns all state is correct, interrupts are enabled and the
> - * subsequent functions can be instrumented.
> - *
> - * This is the combination of enter_from_user_mode() and
> - * syscall_enter_from_user_mode_work() to be used when there is no
> - * architecture specific work to be done between the two.
> - *
> - * Returns: The original or a modified syscall number. See
> - * syscall_enter_from_user_mode_work() for further explanation.
> - */
> -static __always_inline long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)
> -{
> -	long ret;
> -
> -	enter_from_user_mode(regs);
> -
> -	instrumentation_begin();
> -	local_irq_enable();
> -	ret = syscall_enter_from_user_mode_work(regs, syscall);
> -	instrumentation_end();
> -
> -	return ret;
> -}
> -
>  /*
> - * If SYSCALL_EMU is set, then the only reason to report is when
> - * SINGLESTEP is set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall
> - * instruction has been already reported in syscall_enter_from_user_mode().
> + * If SYSCALL_EMU is set, then the only reason to report is when SINGLESTEP is
> + * set (i.e. PTRACE_SYSEMU_SINGLESTEP).  This syscall instruction has been
> + * already reported in syscall_enter_from_user_mode_work().
>   */
>  static __always_inline bool report_single_step(unsigned long work)
>  {
> --- a/include/linux/irq-entry-common.h
> +++ b/include/linux/irq-entry-common.h
> @@ -49,9 +49,9 @@
>   * Defaults to an empty implementation. Can be replaced by architecture
>   * specific code.
>   *
> - * Invoked from syscall_enter_from_user_mode() in the non-instrumentable
> - * section. Use __always_inline so the compiler cannot push it out of line
> - * and make it instrumentable.
> + * Invoked from enter_from_user_mode_syscall_and_randomize_stack() in the
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Probably syscall_enter_from_user_mode_randomize_stack()? But the
reality is it's only ever invoked from enter_from_user_mode(), which is
below in the same file (include/linux/irq-entry-common.h).

Granted, that's an always inline function, and it's used by both macros
you added (since the second one uses the first one).

> + * non-instrumentable section. Use __always_inline so the compiler cannot push
> + * it out of line and make it instrumentable.
>   */
>  static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs);
>