Re: [PATCH v2 13/18] uaccess: generalize access_ok()

Dinh Nguyen
2022-02-25T04:31:45Z

On 2/16/22 07:13, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> There are many different ways that access_ok() is defined across
> architectures, but in the end, they all just compare against the
> user_addr_max() value or they accept anything.
>
> Provide one definition that works for most architectures, checking
> against TASK_SIZE_MAX for user processes or skipping the check inside
> of uaccess_kernel() sections.
>
> For architectures without CONFIG_SET_FS(), this should be the fastest
> check, as it comes down to a single comparison of a pointer against a
> compile-time constant, while the architecture specific versions tend to
> do something more complex for historic reasons or get something wrong.
>
> Type checking for __user annotations is handled inconsistently across
> architectures, but this is easily simplified as well by using an inline
> function that takes a 'const void __user *' argument. A handful of
> callers need an extra __user annotation for this.
>
> Some architectures had trick to use 33-bit or 65-bit arithmetic on the
> addresses to calculate the overflow, however this simpler version uses
> fewer registers, which means it can produce better object code in the
> end despite needing a second (statically predicted) branch.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Mark Rutland <mark.rutland@arm.com> [arm64, asm-generic]
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> arch/Kconfig | 7 ++++
> arch/alpha/include/asm/uaccess.h | 34 +++------------
> arch/arc/include/asm/uaccess.h | 29 -------------
> arch/arm/include/asm/uaccess.h | 20 +--------
> arch/arm64/include/asm/uaccess.h | 11 ++---
> arch/csky/include/asm/uaccess.h | 8 ----
> arch/hexagon/include/asm/uaccess.h | 25 ------------
> arch/ia64/include/asm/uaccess.h | 5 +--
> arch/m68k/Kconfig.cpu | 1 +
> arch/m68k/include/asm/uaccess.h | 19 +--------
> arch/microblaze/include/asm/uaccess.h | 8 +---
> arch/mips/include/asm/uaccess.h | 29 +------------
> arch/nds32/include/asm/uaccess.h | 7 +---
> arch/nios2/include/asm/uaccess.h | 11 +----

Acked-by: Dinh Nguyen <dinguyen@kernel.org>