[PATCH 2/6] powerpc: Provide syscall wrapper

[Arnd Bergmann]

On Wed, Jun 1, 2022 at 7:48 AM Rohan McLure <rmclure at linux.ibm.com> wrote:
>
> Syscall wrapper implemented as per s390, x86, arm64, providing the
> option for gprs to be cleared on entry to the kernel, reducing caller
> influence influence on speculation within syscall routine. The wrapper
> is a macro that emits syscall handler implementations with parameters
> passed by stack pointer.
>
> For platforms supporting this syscall wrapper, emit symbols with usual
> in-register parameters (`sys...`) to support calls to syscall handlers
> from within the kernel.

Nice work!

> Syscalls are wrapped on all platforms except Cell processor. SPUs require
> access syscall prototypes which are omitted with ARCH_HAS_SYSCALL_WRAPPER
> enabled.

Right, I think it's ok to leave out the SPU side. In the long run, I
would like to
go back to requiring the prototypes for everything on all architectures, to
enforce type checking, but that's a separate piece of work.

> +/*
> + * For PowerPC specific syscall implementations, wrapper takes exact name and
> + * return type for a given function.
> + */
> +
> +#ifdef CONFIG_ARCH_HAS_SYSCALL_WRAPPER
> +#define PPC_SYSCALL_DEFINE(x, type, name, ...)                                 \
> +       asmlinkage type __powerpc_##name(const struct pt_regs *regs);           \
> +       ALLOW_ERROR_INJECTION(__powerpc_##name, ERRNO);                         \
> +       type sys_##name(__MAP(x,__SC_DECL,__VA_ARGS__));                        \
> +       static type __se_##name(__MAP(x,__SC_LONG,__VA_ARGS__));                \
> +       static inline type __do_##name(__MAP(x,__SC_DECL,__VA_ARGS__));         \

What is the benefit of having a separate set of macros for this? I think that
adds more complexity than it saves in the end.

> @@ -68,52 +69,63 @@ unsigned long compat_sys_mmap2(unsigned long addr, size_t len,
>  #define merge_64(high, low) ((u64)high << 32) | low
>  #endif
>
> -compat_ssize_t compat_sys_pread64(unsigned int fd, char __user *ubuf, compat_size_t count,
> -                            u32 reg6, u32 pos1, u32 pos2)
> +PPC_SYSCALL_DEFINE(6, compat_ssize_t, compat_sys_pread64,
> +                  unsigned int, fd,
> +                  char __user *, ubuf, compat_size_t, count,
> +                  u32, reg6, u32, pos1, u32, pos2)
>  {
>         return ksys_pread64(fd, ubuf, count, merge_64(pos1, pos2));
>  }

We now have generalized versions of most of these system calls, as of 5.19-rc1
with the addition of the riscv compat support. I think it would be
best to try removing
the powerpc private versions wherever possible and use the common version,
modifying it further where necessary.

If this doesn't work for some of the syscalls, can you use the
COMPAT_SYSCALL_DEFINE for those in place of PPC_SYSCALL_DEFINE?

     Arnd