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

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Message-ID: <e9595d8b-d1e2-4c6a-b097-6f4f08d29866@csgroup.eu>
Date: Tue, 15 Oct 2024 19:43:56 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Luming Yu <luming.yu@...ngroup.cn>, linuxppc-dev@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, mpe@...erman.id.au, npiggin@...il.com,
 jialong.yang@...ngroup.cn, luming.yu@...il.com
Subject: Re: [PATCH 1/7] powerpc/entry: convert to common and generic entry



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.yu@...ngroup.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;
>   }