Le 12/10/2024 à 05:56, Luming Yu a écrit :

quoted

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 <redacted>
---
  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(-)

...

quoted

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 ?

I assume the common entry would take over th details.
So I just made the switch from the high level call.

As you said as the subtle ABI requirement about regs->r3 needs to
be restored, I'm wondering which test can capture the lost
ABI feature. As simple Boot test is insufficient, what is the test set
that can capture it?

I will look into the details late this week.

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 ?

quoted

  		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;
  }