On 7/8/2026 3:06 AM, Thomas Gleixner wrote:
> Randomizing the syscall stack can only happen after state is established
> via enter_from_user_mode() or syscall_enter_from_user_mode(). The earlier
> it happens the better.
>
> Provide two new macros to consolidate that:
>
> - enter_from_user_mode_randomize_stack()
> enter_from_user_mode();
> add_random_kstack_offset_irqsoff();
>
> - syscall_enter_from_user_mode_randomize_stack()
> enter_from_user_mode_randomize_stack();
> syscall_enter_from_user_mode_work();
>
> to reduce boiler plate code.
>
> Those are macros and not inline functions as the latter would limit the
> stack randomization scope to the inline function itself.
>
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
> include/linux/entry-common.h | 56
> +++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 56 insertions(+)
>
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -6,6 +6,7 @@
> #include <linux/irq-entry-common.h>
> #include <linux/livepatch.h>
> #include <linux/ptrace.h>
> +#include <linux/randomize_kstack.h>
> #include <linux/resume_user_mode.h>
> #include <linux/seccomp.h>
> #include <linux/sched.h>
> @@ -150,6 +151,61 @@ static __always_inline long syscall_ente
> }
>
> /**
> + * enter_from_user_mode_randomize_stack - Establish state and add stack
> randomization
> + * before invoking
> syscall_enter_from_user_mode_work()
> + * @regs: Pointer to currents pt_regs
> + *
> + * 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 still disabled and the
> + * subsequent functions can be instrumented.
> + *
> + * Implemented as a macro so that the stack randomization is effective
> + * throughout the function in which it is invoked. An inline would only make
> it
> + * effective in the scope of the inline function.
> + */
> +#define enter_from_user_mode_randomize_stack(regs) \
> +do { \
> + enter_from_user_mode(regs); \
> + instrumentation_begin(); \
> + add_random_kstack_offset_irqsoff(); \
> + instrumentation_end(); \
> +} while (0)
Perhaps this new function can also be reused when the ARM64 is switched
to the generic entry as the irq also disabled now.
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -64,7 +64,7 @@ static void noinstr arm64_exit_to_kernel_mode(struct
pt_regs *regs,
static __always_inline void arm64_syscall_enter_from_user_mode(struct
pt_regs *regs)
{
- enter_from_user_mode(regs);
+ enter_from_user_mode_randomize_stack(regs);
mte_disable_tco_entry(current);
sme_enter_from_user_mode();
}
diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c
index e0a98fac3b85..42ac02573b66 100644
--- a/arch/arm64/kernel/syscall.c
+++ b/arch/arm64/kernel/syscall.c
@@ -6,7 +6,6 @@
#include <linux/errno.h>
#include <linux/nospec.h>
#include <linux/ptrace.h>
-#include <linux/randomize_kstack.h>
#include <linux/syscalls.h>
#include <asm/debug-monitors.h>
@@ -42,8 +41,6 @@ static void invoke_syscall(struct pt_regs *regs,
unsigned int scno,
{
long ret;
- add_random_kstack_offset();
-
if (likely(scno < sc_nr)) {
syscall_fn_t syscall_fn;
syscall_fn = syscall_table[array_index_nospec(scno, sc_nr)];
> +
> +/**
> + * syscall_enter_from_user_mode_randomize_stack - 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_randomize_stack() 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.
> + *
> + * Implemented as a macro to make stack randomization effective in the
> calling
> + * scope.
> + */
> +#define syscall_enter_from_user_mode_randomize_stack(regs, syscall) \
> +({ \
> + enter_from_user_mode_randomize_stack(regs); \
> + \
> + instrumentation_begin(); \
> + local_irq_enable(); \
> + long _ret = syscall_enter_from_user_mode_work(regs, syscall); \
> + instrumentation_end(); \
> + \
> + _ret; \
> +})
> +
> +/**
> * syscall_enter_from_user_mode - Establish state and check and handle work
> * before invoking a syscall
> * @regs: Pointer to currents pt_regs
>
