Re: [PATCH 10/10] powerpc: remove address space overrides using set_fs()

Christophe Leroy
2020-09-02T06:15:26Z

Le 27/08/2020 à 17:00, Christoph Hellwig a écrit :
> Stop providing the possibility to override the address space using
> set_fs() now that there is no need for that any more.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/powerpc/Kconfig | 1 -
> arch/powerpc/include/asm/processor.h | 7 ---
> arch/powerpc/include/asm/thread_info.h | 5 +--
> arch/powerpc/include/asm/uaccess.h | 62 ++++++++------------------
> arch/powerpc/kernel/signal.c | 3 --
> arch/powerpc/lib/sstep.c | 6 +--
> 6 files changed, 22 insertions(+), 62 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 7fe3531ad36a77..39727537d39701 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -8,62 +8,36 @@
> #include <asm/extable.h>
> #include <asm/kup.h>
>
> -/*
> - * The fs value determines whether argument validity checking should be
> - * performed or not. If get_fs() == USER_DS, checking is performed, with
> - * get_fs() == KERNEL_DS, checking is bypassed.
> - *
> - * For historical reasons, these macros are grossly misnamed.
> - *
> - * The fs/ds values are now the highest legal address in the "segment".
> - * This simplifies the checking in the routines below.
> - */
> -
> -#define MAKE_MM_SEG(s) ((mm_segment_t) { (s) })
> -
> -#define KERNEL_DS MAKE_MM_SEG(~0UL)
> #ifdef __powerpc64__
> /* We use TASK_SIZE_USER64 as TASK_SIZE is not constant */
> -#define USER_DS MAKE_MM_SEG(TASK_SIZE_USER64 - 1)
> -#else
> -#define USER_DS MAKE_MM_SEG(TASK_SIZE - 1)
> -#endif
> -
> -#define get_fs() (current->thread.addr_limit)
> +#define TASK_SIZE_MAX TASK_SIZE_USER64
>
> -static inline void set_fs(mm_segment_t fs)
> +static inline bool __access_ok(unsigned long addr, unsigned long size)
> {
> - current->thread.addr_limit = fs;
> - /* On user-mode return check addr_limit (fs) is correct */
> - set_thread_flag(TIF_FSCHECK);
> + if (addr >= TASK_SIZE_MAX)
> + return false;
> + /*
> + * This check is sufficient because there is a large enough gap between
> + * user addresses and the kernel addresses.
> + */
> + return size <= TASK_SIZE_MAX;
> }
> -
> -#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
> -#define user_addr_max() (get_fs().seg)
> -
> -#ifdef __powerpc64__
> -/*
> - * This check is sufficient because there is a large enough
> - * gap between user addresses and the kernel addresses
> - */
> -#define __access_ok(addr, size, segment) \
> - (((addr) <= (segment).seg) && ((size) <= (segment).seg))
> -
> #else
> +#define TASK_SIZE_MAX TASK_SIZE
>
> -static inline int __access_ok(unsigned long addr, unsigned long size,
> - mm_segment_t seg)
> +static inline bool __access_ok(unsigned long addr, unsigned long size)
> {
> - if (addr > seg.seg)
> - return 0;
> - return (size == 0 || size - 1 <= seg.seg - addr);
> + if (addr >= TASK_SIZE_MAX)
> + return false;
> + if (size == 0)
> + return false;

__access_ok() was returning true when size == 0 up to now. Any reason to
return false now ?

> + return size <= TASK_SIZE_MAX - addr;
> }
> -
> -#endif
> +#endif /* __powerpc64__ */
>
> #define access_ok(addr, size) \
> (__chk_user_ptr(addr), \
> - __access_ok((__force unsigned long)(addr), (size), get_fs()))
> + __access_ok((unsigned long)(addr), (size)))
>
> /*
> * These are the main single-value transfer routines. They automatically

Christophe