Re: [PATCH v4 10/20] powerpc: Use common syscall handler type

["Nicholas Piggin" <npiggin@gmail.com>]

On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:
> Cause syscall handlers to be typed as follows when called indirectly
> throughout the kernel.
>
> typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
>                            unsigned long, unsigned long, unsigned long);

The point is... better type checking?

>
> Since both 32 and 64-bit abis allow for at least the first six
> machine-word length parameters to a function to be passed by registers,
> even handlers which admit fewer than six parameters may be viewed as
> having the above type.
>
> Fixup comparisons in VDSO to avoid pointer-integer comparison. Introduce
> explicit cast on systems with SPUs.
>
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> V1 -> V2: New patch.
> V2 -> V3: Remove unnecessary cast from const syscall_fn to syscall_fn
> ---
>  arch/powerpc/include/asm/syscall.h          | 7 +++++--
>  arch/powerpc/include/asm/syscalls.h         | 1 +
>  arch/powerpc/kernel/systbl.c                | 6 +++---
>  arch/powerpc/kernel/vdso.c                  | 4 ++--
>  arch/powerpc/platforms/cell/spu_callbacks.c | 6 +++---
>  5 files changed, 14 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
> index 25fc8ad9a27a..d2a8dfd5de33 100644
> --- a/arch/powerpc/include/asm/syscall.h
> +++ b/arch/powerpc/include/asm/syscall.h
> @@ -14,9 +14,12 @@
>  #include <linux/sched.h>
>  #include <linux/thread_info.h>
>  
> +typedef long (*syscall_fn)(unsigned long, unsigned long, unsigned long,
> +			   unsigned long, unsigned long, unsigned long);
> +
>  /* ftrace syscalls requires exporting the sys_call_table */
> -extern const unsigned long sys_call_table[];
> -extern const unsigned long compat_sys_call_table[];
> +extern const syscall_fn sys_call_table[];
> +extern const syscall_fn compat_sys_call_table[];

Ah you constify it in this patch. I think the previous patch should have
kept the const, and it should keep the unsigned long type rather than
use void *. Either that or do this patch first.

>  static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
>  {
> diff --git a/arch/powerpc/include/asm/syscalls.h b/arch/powerpc/include/asm/syscalls.h
> index 91417dee534e..e979b7593d2b 100644
> --- a/arch/powerpc/include/asm/syscalls.h
> +++ b/arch/powerpc/include/asm/syscalls.h
> @@ -8,6 +8,7 @@
>  #include <linux/types.h>
>  #include <linux/compat.h>
>  
> +#include <asm/syscall.h>
>  #ifdef CONFIG_PPC64
>  #include <asm/syscalls_32.h>
>  #endif

Is this necessary or should be in another patch?

> diff --git a/arch/powerpc/kernel/systbl.c b/arch/powerpc/kernel/systbl.c
> index 99ffdfef6b9c..b88a9c2a1f50 100644
> --- a/arch/powerpc/kernel/systbl.c
> +++ b/arch/powerpc/kernel/systbl.c
> @@ -21,10 +21,10 @@
>  #define __SYSCALL(nr, entry) [nr] = __powerpc_##entry,
>  #define __powerpc_sys_ni_syscall	sys_ni_syscall
>  #else
> -#define __SYSCALL(nr, entry) [nr] = entry,
> +#define __SYSCALL(nr, entry) [nr] = (void *) entry,
>  #endif

Also perhaps this should have been in the prior pach and this pach
should change the cast from void to syscall_fn ?

>  
> -void *sys_call_table[] = {
> +const syscall_fn sys_call_table[] = {
>  #ifdef CONFIG_PPC64
>  #include <asm/syscall_table_64.h>
>  #else
> @@ -35,7 +35,7 @@ void *sys_call_table[] = {
>  #ifdef CONFIG_COMPAT
>  #undef __SYSCALL_WITH_COMPAT
>  #define __SYSCALL_WITH_COMPAT(nr, native, compat)	__SYSCALL(nr, compat)
> -void *compat_sys_call_table[] = {
> +const syscall_fn compat_sys_call_table[] = {
>  #include <asm/syscall_table_32.h>
>  };
>  #endif /* CONFIG_COMPAT */
> diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
> index 0da287544054..080c9e7de0c0 100644
> --- a/arch/powerpc/kernel/vdso.c
> +++ b/arch/powerpc/kernel/vdso.c
> @@ -313,10 +313,10 @@ static void __init vdso_setup_syscall_map(void)
>  	unsigned int i;
>  
>  	for (i = 0; i < NR_syscalls; i++) {
> -		if (sys_call_table[i] != (unsigned long)&sys_ni_syscall)
> +		if (sys_call_table[i] != (void *)&sys_ni_syscall)
>  			vdso_data->syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
>  		if (IS_ENABLED(CONFIG_COMPAT) &&
> -		    compat_sys_call_table[i] != (unsigned long)&sys_ni_syscall)
> +		    compat_sys_call_table[i] != (void *)&sys_ni_syscall)

Also these.

Thanks,
Nick

>  			vdso_data->compat_syscall_map[i >> 5] |= 0x80000000UL >> (i & 0x1f);
>  	}
>  }
> diff --git a/arch/powerpc/platforms/cell/spu_callbacks.c b/arch/powerpc/platforms/cell/spu_callbacks.c
> index fe0d8797a00a..e780c14c5733 100644
> --- a/arch/powerpc/platforms/cell/spu_callbacks.c
> +++ b/arch/powerpc/platforms/cell/spu_callbacks.c
> @@ -34,15 +34,15 @@
>   *	mbind, mq_open, ipc, ...
>   */
>  
> -static void *spu_syscall_table[] = {
> +static const syscall_fn spu_syscall_table[] = {
>  #define __SYSCALL_WITH_COMPAT(nr, entry, compat) __SYSCALL(nr, entry)
> -#define __SYSCALL(nr, entry) [nr] = entry,
> +#define __SYSCALL(nr, entry) [nr] = (void *) entry,
>  #include <asm/syscall_table_spu.h>
>  };
>  
>  long spu_sys_callback(struct spu_syscall_block *s)
>  {
> -	long (*syscall)(u64 a1, u64 a2, u64 a3, u64 a4, u64 a5, u64 a6);
> +	syscall_fn syscall;
>  
>  	if (s->nr_ret >= ARRAY_SIZE(spu_syscall_table)) {
>  		pr_debug("%s: invalid syscall #%lld", __func__, s->nr_ret);
> -- 
> 2.34.1