On 7/8/2026 3:06 AM, Thomas Gleixner wrote:
> These functions integrate the stack randomization.
>
> syscall_enter_from_user_mode_randomize_stack() has the advantage that the
> randomization happens early right after enter_from_user_mode().
>
> In both cases also the overhead of get/put_cpu_var() in
> add_random_kstack_offset() is avoided.
>
> No functional change.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> Cc: [email protected]
> ---
> arch/x86/entry/syscall_32.c | 19 +++++--------------
> arch/x86/entry/syscall_64.c | 3 +--
> arch/x86/include/asm/entry-common.h | 1 -
> 3 files changed, 6 insertions(+), 17 deletions(-)
Reviewed-by: Jinjie Ruan <[email protected]>
>
> --- a/arch/x86/entry/syscall_32.c
> +++ b/arch/x86/entry/syscall_32.c
> @@ -142,10 +142,9 @@ static __always_inline bool int80_is_ext
> * int80_is_external() below which calls into the APIC driver.
> * Identical for soft and external interrupts.
> */
> - enter_from_user_mode(regs);
> + enter_from_user_mode_randomize_stack(regs);
>
> instrumentation_begin();
> - add_random_kstack_offset();
>
> /* Validate that this is a soft interrupt to the extent possible */
> if (unlikely(int80_is_external()))
> @@ -210,11 +209,9 @@ DEFINE_FREDENTRY_RAW(int80_emulation)
> {
> int nr;
>
> - enter_from_user_mode(regs);
> + enter_from_user_mode_randomize_stack(regs);
>
> instrumentation_begin();
> - add_random_kstack_offset();
> -
> /*
> * FRED pushed 0 into regs::orig_ax and regs::ax contains the
> * syscall number.
> @@ -252,10 +249,10 @@ DEFINE_FREDENTRY_RAW(int80_emulation)
> * orig_ax, the int return value truncates it. This matches
> * the semantics of syscall_get_nr().
> */
> - nr = syscall_enter_from_user_mode(regs, nr);
> + nr = syscall_enter_from_user_mode_randomize_stack(regs, nr);
> +
> instrumentation_begin();
>
> - add_random_kstack_offset();
> do_syscall_32_irqs_on(regs, nr);
>
> instrumentation_end();
> @@ -268,15 +265,9 @@ static noinstr bool __do_fast_syscall_32
> int nr = syscall_32_enter(regs);
> int res;
>
> - /*
> - * This cannot use syscall_enter_from_user_mode() as it has to
> - * fetch EBP before invoking any of the syscall entry work
> - * functions.
> - */
> - enter_from_user_mode(regs);
> + enter_from_user_mode_randomize_stack(regs);
>
> instrumentation_begin();
> - add_random_kstack_offset();
> local_irq_enable();
> /* Fetch EBP from where the vDSO stashed it. */
> if (IS_ENABLED(CONFIG_X86_64)) {
> --- a/arch/x86/entry/syscall_64.c
> +++ b/arch/x86/entry/syscall_64.c
> @@ -86,10 +86,9 @@ static __always_inline bool do_syscall_x
> /* Returns true to return using SYSRET, or false to use IRET */
> __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
> {
> - nr = syscall_enter_from_user_mode(regs, nr);
> + nr = syscall_enter_from_user_mode_randomize_stack(regs, nr);
>
> instrumentation_begin();
> - add_random_kstack_offset();
>
> if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1)
> {
> /* Invalid system call, but still a system call. */
> --- a/arch/x86/include/asm/entry-common.h
> +++ b/arch/x86/include/asm/entry-common.h
> @@ -2,7 +2,6 @@
> #ifndef _ASM_X86_ENTRY_COMMON_H
> #define _ASM_X86_ENTRY_COMMON_H
>
> -#include <linux/randomize_kstack.h>
> #include <linux/user-return-notifier.h>
>
> #include <asm/nospec-branch.h>
>
