[PATCH v2 5/8] powerpc: copy_thread differentiate kthreads and user mode threads
Nicholas Piggin
npiggin at gmail.com
Sat Mar 25 23:29:01 AEDT 2023
When copy_thread is given a kernel function to run in arg->fn, this
does not necessarily mean it is a kernel thread. User threads can be
created this way (e.g., kernel_init, see also x86's copy_thread()).
These threads run a kernel function which may call kernel_execve()
and return, which returns like a userspace exec(2) syscall.
Kernel threads are to be differentiated with PF_KTHREAD, will always
have arg->fn set, and should never return from that function, instead
calling kthread_exit() to exit.
Create separate paths for the kthread and user kernel thread creation
logic. The kthread path will never exit and does not require a user
interrupt frame, so it gets a minimal stack frame.
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/include/asm/thread_info.h | 2 +
arch/powerpc/kernel/process.c | 98 ++++++++++++++++----------
2 files changed, 64 insertions(+), 36 deletions(-)
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index af58f1ed3952..6c9e70402922 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -175,9 +175,11 @@ static inline bool test_thread_local_flags(unsigned int flags)
#ifdef CONFIG_COMPAT
#define is_32bit_task() (test_thread_flag(TIF_32BIT))
#define is_tsk_32bit_task(tsk) (test_tsk_thread_flag(tsk, TIF_32BIT))
+#define clear_tsk_compat_task(tsk) (clear_tsk_thread_flag(p, TIF_32BIT))
#else
#define is_32bit_task() (IS_ENABLED(CONFIG_PPC32))
#define is_tsk_32bit_task(tsk) (IS_ENABLED(CONFIG_PPC32))
+#define clear_tsk_compat_task(tsk) do { } while (0)
#endif
#if defined(CONFIG_PPC64)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index c537bebb5dd2..7b016f958e8b 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1738,10 +1738,7 @@ static void setup_ksp_vsid(struct task_struct *p, unsigned long sp)
*/
int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
{
- unsigned long clone_flags = args->flags;
- unsigned long usp = args->stack;
- unsigned long tls = args->tls;
- struct pt_regs *childregs, *kregs;
+ struct pt_regs *kregs; /* Switch frame regs */
extern void ret_from_fork(void);
extern void ret_from_fork_scv(void);
extern void ret_from_kernel_thread(void);
@@ -1754,45 +1751,76 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
klp_init_thread_info(p);
- /* Create initial stack frame. */
- sp -= STACK_USER_INT_FRAME_SIZE;
- *(unsigned long *)(sp + STACK_INT_FRAME_MARKER) = STACK_FRAME_REGS_MARKER;
-
- /* Copy registers */
- childregs = (struct pt_regs *)(sp + STACK_INT_FRAME_REGS);
- if (unlikely(args->fn)) {
+ if (unlikely(p->flags & PF_KTHREAD)) {
/* kernel thread */
+
+ /* Create initial minimum stack frame. */
+ sp -= STACK_FRAME_MIN_SIZE;
((unsigned long *)sp)[0] = 0;
- memset(childregs, 0, sizeof(struct pt_regs));
- childregs->gpr[1] = sp + STACK_USER_INT_FRAME_SIZE;
-#ifdef CONFIG_PPC64
- clear_tsk_thread_flag(p, TIF_32BIT);
- childregs->softe = IRQS_ENABLED;
-#endif
- p->thread.regs = NULL; /* no user register state */
- ti->flags |= _TIF_RESTOREALL;
+
f = ret_from_kernel_thread;
+ p->thread.regs = NULL; /* no user register state */
+ clear_tsk_compat_task(p);
} else {
/* user thread */
- struct pt_regs *regs = current_pt_regs();
- *childregs = *regs;
- if (usp)
- childregs->gpr[1] = usp;
- ((unsigned long *)sp)[0] = childregs->gpr[1];
- p->thread.regs = childregs;
- if (clone_flags & CLONE_SETTLS) {
- if (!is_32bit_task())
- childregs->gpr[13] = tls;
+ struct pt_regs *childregs;
+
+ /* Create initial user return stack frame. */
+ sp -= STACK_USER_INT_FRAME_SIZE;
+ *(unsigned long *)(sp + STACK_INT_FRAME_MARKER) = STACK_FRAME_REGS_MARKER;
+
+ childregs = (struct pt_regs *)(sp + STACK_INT_FRAME_REGS);
+
+ if (unlikely(args->fn)) {
+ /*
+ * A user space thread, but it first runs a kernel
+ * thread, and then returns as though it had called
+ * execve rather than fork, so user regs will be
+ * filled in (e.g., by kernel_execve()).
+ */
+ ((unsigned long *)sp)[0] = 0;
+ memset(childregs, 0, sizeof(struct pt_regs));
+#ifdef CONFIG_PPC64
+ childregs->softe = IRQS_ENABLED;
+#endif
+ ti->flags |= _TIF_RESTOREALL;
+ f = ret_from_kernel_thread;
+ } else {
+ struct pt_regs *regs = current_pt_regs();
+ unsigned long clone_flags = args->flags;
+ unsigned long usp = args->stack;
+
+ /* Copy registers */
+ *childregs = *regs;
+ if (usp)
+ childregs->gpr[1] = usp;
+ ((unsigned long *)sp)[0] = childregs->gpr[1];
+#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
+ WARN_ON_ONCE(childregs->softe != IRQS_ENABLED);
+#endif
+ if (clone_flags & CLONE_SETTLS) {
+ unsigned long tls = args->tls;
+
+ if (!is_32bit_task())
+ childregs->gpr[13] = tls;
+ else
+ childregs->gpr[2] = tls;
+ }
+
+ if (trap_is_scv(regs))
+ f = ret_from_fork_scv;
else
- childregs->gpr[2] = tls;
+ f = ret_from_fork;
}
- if (trap_is_scv(regs))
- f = ret_from_fork_scv;
- else
- f = ret_from_fork;
+#ifdef CONFIG_PPC64
+ if (cpu_has_feature(CPU_FTR_HAS_PPR))
+ childregs->ppr = DEFAULT_PPR;
+#endif
+
+ childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);
+ p->thread.regs = childregs;
}
- childregs->msr &= ~(MSR_FP|MSR_VEC|MSR_VSX);
/*
* The way this works is that at some point in the future
@@ -1843,8 +1871,6 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
p->thread.dscr_inherit = current->thread.dscr_inherit;
p->thread.dscr = mfspr(SPRN_DSCR);
}
- if (cpu_has_feature(CPU_FTR_HAS_PPR))
- childregs->ppr = DEFAULT_PPR;
p->thread.tidr = 0;
#endif
--
2.37.2
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