Re: [PATCH 1/7] powerpc/entry: convert to common and generic entry

[Christophe Leroy]

Le 12/10/2024 à 05:56, Luming Yu a écrit :
convert powerpc entry code in syscall and fault to use syscall_work
and irqentry_state as well as common calls implemented in generic
entry infrastructure.

Signed-off-by: Luming Yu <luming...@shingroup.cn>
---
  arch/powerpc/Kconfig                   | 1 +
  arch/powerpc/include/asm/hw_irq.h      | 5 +++++
  arch/powerpc/include/asm/processor.h   | 6 ++++++
  arch/powerpc/include/asm/syscall.h     | 5 +++++
  arch/powerpc/include/asm/thread_info.h | 1 +
  arch/powerpc/kernel/syscall.c          | 5 ++++-
  arch/powerpc/mm/fault.c                | 3 +++
  7 files changed, 25 insertions(+), 1 deletion(-)


...

diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c
index 77fedb190c93..e0338bd8d383 100644
--- a/arch/powerpc/kernel/syscall.c
+++ b/arch/powerpc/kernel/syscall.c
@@ -3,6 +3,7 @@
  #include <linux/compat.h>
  #include <linux/context_tracking.h>
  #include <linux/randomize_kstack.h>
+#include <linux/entry-common.h>
  
  #include <asm/interrupt.h>
  #include <asm/kup.h>
@@ -131,7 +132,7 @@ notrace long system_call_exception(struct pt_regs *regs, 
unsigned long r0)
                 * and the test against NR_syscalls will fail and the return
                 * value to be used is in regs->gpr[3].
                 */
-               r0 = do_syscall_trace_enter(regs);
+               r0 = syscall_enter_from_user_mode(regs, r0);

Can you provide details on how this works ?

For instance, do_syscall_trace_enter() was calling do_seccomp().
do_seccomp() sets regs->r3 to -ENOSYS then calls __secure_computing().

Now you call syscall_enter_from_user_mode() instead which calls 
syscall_enter_from_user_mode_work() which calls syscall_trace_enter() 
which calls  __secure_computing() but without seting regs->r3 to -ENOSYS.

So what will be returned by the below return when 
syscall_enter_from_user_mode returns -1 ?

                if (unlikely(r0 >= NR_syscalls))
                        return regs->gpr[3];
  
@@ -184,6 +185,8 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0)
         * So the resulting 6 or 7 bits of entropy is seen in SP[9:4] or 
SP[9:3].
         */
        choose_random_kstack_offset(mftb());
+       /*common entry*/
+       syscall_exit_to_user_mode(regs);
  
  	return ret;
  }