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[Backport v4.2-branch] arch: arm: start threads on privileged stack #97306

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[Backport v4.2-branch] arch: arm: start threads on privileged stack #97306

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73 changes: 50 additions & 23 deletions arch/arm/core/cortex_a_r/thread.c
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
/*
* Copyright (c) 2013-2014 Wind River Systems, Inc.
* Copyright (c) 2021 Lexmark International, Inc.
* Copyright 2025 Arm Limited and/or its affiliates <[email protected]>
*
* SPDX-License-Identifier: Apache-2.0
*/
Expand Down Expand Up @@ -37,6 +38,34 @@
*/
#define DEFAULT_EXC_RETURN 0xFD;

#ifdef CONFIG_USERSPACE
static void setup_priv_stack(struct k_thread *thread)
{
/* Set up privileged stack before entering user mode */
thread->arch.priv_stack_start = (uint32_t)z_priv_stack_find(thread->stack_obj);

/* CONFIG_PRIVILEGED_STACK_SIZE does not account for MPU_GUARD_ALIGN_AND_SIZE or
* MPU_GUARD_ALIGN_AND_SIZE_FLOAT. Therefore, we must compute priv_stack_end here before
* adjusting priv_stack_start for the mpu guard alignment
*/
thread->arch.priv_stack_end = thread->arch.priv_stack_start + CONFIG_PRIVILEGED_STACK_SIZE;

#if defined(CONFIG_MPU_STACK_GUARD)
/* Stack guard area reserved at the bottom of the thread's
* privileged stack. Adjust the available (writable) stack
* buffer area accordingly.
*/
#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
thread->arch.priv_stack_start +=
((thread->arch.mode & Z_ARM_MODE_MPU_GUARD_FLOAT_Msk) != 0) ?
MPU_GUARD_ALIGN_AND_SIZE_FLOAT : MPU_GUARD_ALIGN_AND_SIZE;
#else
thread->arch.priv_stack_start += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */
#endif /* CONFIG_MPU_STACK_GUARD */
}
#endif

/* An initial context, to be "restored" by z_arm_pendsv(), is put at the other
* end of the stack, and thus reusable by the stack when not needed anymore.
*
Expand Down Expand Up @@ -80,7 +109,10 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,

iframe = Z_STACK_PTR_TO_FRAME(struct __basic_sf, stack_ptr);
#if defined(CONFIG_USERSPACE)
thread->arch.priv_stack_start = 0;
if ((thread->base.user_options & K_USER) != 0) {
setup_priv_stack(thread);
iframe = Z_STACK_PTR_TO_FRAME(struct __basic_sf, thread->arch.priv_stack_end);
iframe->pc = (uint32_t)arch_user_mode_enter;
} else {
iframe->pc = (uint32_t)z_thread_entry;
Expand Down Expand Up @@ -122,9 +154,6 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
thread->arch.mode |= Z_ARM_MODE_MPU_GUARD_FLOAT_Msk;
}
#endif
#if defined(CONFIG_USERSPACE)
thread->arch.priv_stack_start = 0;
#endif
#endif
/*
* initial values in all other registers/thread entries are
Expand Down Expand Up @@ -196,10 +225,8 @@ static inline void z_arm_thread_stack_info_adjust(struct k_thread *thread,
FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
void *p1, void *p2, void *p3)
{
uint32_t sp_is_priv = 1;

/* Set up privileged stack before entering user mode */
_current->arch.priv_stack_start =
(uint32_t)z_priv_stack_find(_current->stack_obj);
#if defined(CONFIG_MPU_STACK_GUARD)
#if defined(CONFIG_THREAD_STACK_INFO)
/* We're dropping to user mode which means the guard area is no
Expand All @@ -216,29 +243,29 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
_current->stack_info.start -= MPU_GUARD_ALIGN_AND_SIZE;
_current->stack_info.size += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_THREAD_STACK_INFO */

/* Stack guard area reserved at the bottom of the thread's
* privileged stack. Adjust the available (writable) stack
* buffer area accordingly.
*/
#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
_current->arch.priv_stack_start +=
((_current->arch.mode & Z_ARM_MODE_MPU_GUARD_FLOAT_Msk) != 0) ?
MPU_GUARD_ALIGN_AND_SIZE_FLOAT : MPU_GUARD_ALIGN_AND_SIZE;
#else
_current->arch.priv_stack_start += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */
#endif /* CONFIG_MPU_STACK_GUARD */

#if defined(CONFIG_CPU_AARCH32_CORTEX_R)
_current->arch.priv_stack_end =
_current->arch.priv_stack_start + CONFIG_PRIVILEGED_STACK_SIZE;
#endif
/* 2 ways how arch_user_mode_enter is called:
* - called as part of context switch from z_arm_pendsv, in this case privileged stack is
* already setup and stack pointer points to privileged stack.
* - called directly from k_thread_user_mode_enter, in this case privileged stack is not
* setup and stack pointer points to user stack.
*
* When called from k_thread_user_mode_enter, we need to check and setup the privileged
* stack and then instruct z_arm_userspace_enter to change the PSP to the privileged stack.
* Note that we do not change the PSP in this function to avoid any conflict with compiler's
* sequence which has already pushed stuff on the user stack.
*/
if (0 == _current->arch.priv_stack_start) {
setup_priv_stack(_current);
sp_is_priv = 0;
}

z_arm_userspace_enter(user_entry, p1, p2, p3,
(uint32_t)_current->stack_info.start,
_current->stack_info.size -
_current->stack_info.delta);
_current->stack_info.delta,
sp_is_priv);
CODE_UNREACHABLE;
}

Expand Down
67 changes: 49 additions & 18 deletions arch/arm/core/cortex_m/thread.c
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,35 @@
K_THREAD_STACK_DECLARE(z_main_stack, CONFIG_MAIN_STACK_SIZE);
#endif

#ifdef CONFIG_USERSPACE
static void setup_priv_stack(struct k_thread *thread)
{
/* Set up privileged stack before entering user mode */
thread->arch.priv_stack_start = (uint32_t)z_priv_stack_find(thread->stack_obj);

/* CONFIG_PRIVILEGED_STACK_SIZE does not account for MPU_GUARD_ALIGN_AND_SIZE or
* MPU_GUARD_ALIGN_AND_SIZE_FLOAT. Therefore, we must compute priv_stack_end here before
* adjusting priv_stack_start for the mpu guard alignment
*/
thread->arch.priv_stack_end = thread->arch.priv_stack_start + CONFIG_PRIVILEGED_STACK_SIZE;

#if defined(CONFIG_MPU_STACK_GUARD)
/* Stack guard area reserved at the bottom of the thread's
* privileged stack. Adjust the available (writable) stack
* buffer area accordingly.
*/
#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
thread->arch.priv_stack_start +=
((thread->arch.mode & Z_ARM_MODE_MPU_GUARD_FLOAT_Msk) != 0)
? MPU_GUARD_ALIGN_AND_SIZE_FLOAT
: MPU_GUARD_ALIGN_AND_SIZE;
#else
thread->arch.priv_stack_start += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */
#endif /* CONFIG_MPU_STACK_GUARD */
}
#endif

/* An initial context, to be "restored" by z_arm_pendsv(), is put at the other
* end of the stack, and thus reusable by the stack when not needed anymore.
*
Expand Down Expand Up @@ -87,7 +116,10 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack, char *sta

iframe = Z_STACK_PTR_TO_FRAME(struct __basic_sf, stack_ptr);
#if defined(CONFIG_USERSPACE)
thread->arch.priv_stack_start = 0;
if ((thread->base.user_options & K_USER) != 0) {
setup_priv_stack(thread);
iframe = Z_STACK_PTR_TO_FRAME(struct __basic_sf, thread->arch.priv_stack_end);
iframe->pc = (uint32_t)arch_user_mode_enter;
} else {
iframe->pc = (uint32_t)z_thread_entry;
Expand Down Expand Up @@ -118,9 +150,6 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack, char *sta
thread->arch.mode |= Z_ARM_MODE_MPU_GUARD_FLOAT_Msk;
}
#endif
#if defined(CONFIG_USERSPACE)
thread->arch.priv_stack_start = 0;
#endif
#endif
/*
* initial values in all other registers/thread entries are
Expand Down Expand Up @@ -215,9 +244,8 @@ uint32_t z_arm_mpu_stack_guard_and_fpu_adjust(struct k_thread *thread)
#ifdef CONFIG_USERSPACE
FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry, void *p1, void *p2, void *p3)
{
uint32_t sp_is_priv = 1;

/* Set up privileged stack before entering user mode */
_current->arch.priv_stack_start = (uint32_t)z_priv_stack_find(_current->stack_obj);
#if defined(CONFIG_MPU_STACK_GUARD)
#if defined(CONFIG_THREAD_STACK_INFO)
/* We're dropping to user mode which means the guard area is no
Expand All @@ -234,23 +262,26 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry, void *p1, v
_current->stack_info.start -= MPU_GUARD_ALIGN_AND_SIZE;
_current->stack_info.size += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_THREAD_STACK_INFO */
#endif /* CONFIG_MPU_STACK_GUARD */

/* Stack guard area reserved at the bottom of the thread's
* privileged stack. Adjust the available (writable) stack
* buffer area accordingly.
/* 2 ways how arch_user_mode_enter is called:
* - called as part of context switch from z_arm_pendsv, in this case privileged stack is
* already setup and stack pointer points to privileged stack.
* - called directly from k_thread_user_mode_enter, in this case privileged stack is not
* setup and stack pointer points to user stack.
*
* When called from k_thread_user_mode_enter, we need to check and setup the privileged
* stack and then instruct z_arm_userspace_enter to change the PSP to the privileged stack.
* Note that we do not change the PSP in this function to avoid any conflict with compiler's
* sequence which has already pushed stuff on the user stack.
*/
#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
_current->arch.priv_stack_start +=
((_current->arch.mode & Z_ARM_MODE_MPU_GUARD_FLOAT_Msk) != 0)
? MPU_GUARD_ALIGN_AND_SIZE_FLOAT
: MPU_GUARD_ALIGN_AND_SIZE;
#else
_current->arch.priv_stack_start += MPU_GUARD_ALIGN_AND_SIZE;
#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */
#endif /* CONFIG_MPU_STACK_GUARD */
if (0 == _current->arch.priv_stack_start) {
setup_priv_stack(_current);
sp_is_priv = 0;
}

z_arm_userspace_enter(user_entry, p1, p2, p3, (uint32_t)_current->stack_info.start,
_current->stack_info.size - _current->stack_info.delta);
_current->stack_info.size - _current->stack_info.delta, sp_is_priv);
CODE_UNREACHABLE;
}

Expand Down
3 changes: 2 additions & 1 deletion arch/arm/core/offsets/offsets_aarch32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -45,8 +45,9 @@ GEN_OFFSET_SYM(_thread_arch_t, mode_exc_return);
#endif
#if defined(CONFIG_USERSPACE)
GEN_OFFSET_SYM(_thread_arch_t, priv_stack_start);
#if defined(CONFIG_CPU_AARCH32_CORTEX_R)
GEN_OFFSET_SYM(_thread_arch_t, priv_stack_end);

#if defined(CONFIG_CPU_AARCH32_CORTEX_R)
GEN_OFFSET_SYM(_thread_arch_t, sp_usr);
#endif
#endif
Expand Down
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