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

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On 2/16/22 07:13, Arnd Bergmann wrote:
From: Arnd Bergmann <arnd@xxxxxxxx>

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@xxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx> [arm64, asm-generic]
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
  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@xxxxxxxxxx>




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