uaccess: generalize access_ok()
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]
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Stafford Horne <shorne@gmail.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2022-02-15 17:55:04 +01:00
/* SPDX-License-Identifier: GPL-2.0 */
# ifndef __ASM_GENERIC_ACCESS_OK_H__
# define __ASM_GENERIC_ACCESS_OK_H__
/*
* Checking whether a pointer is valid for user space access .
* These definitions work on most architectures , but overrides can
* be used where necessary .
*/
/*
* architectures with compat tasks have a variable TASK_SIZE and should
* override this to a constant .
*/
# ifndef TASK_SIZE_MAX
# define TASK_SIZE_MAX TASK_SIZE
# endif
# ifndef __access_ok
/*
* ' size ' is a compile - time constant for most callers , so optimize for
* this case to turn the check into a single comparison against a constant
* limit and catch all possible overflows .
* On architectures with separate user address space ( m68k , s390 , parisc ,
* sparc64 ) or those without an MMU , this should always return true .
*
* This version was originally contributed by Jonas Bonn for the
* OpenRISC architecture , and was found to be the most efficient
* for constant ' size ' and ' limit ' values .
*/
static inline int __access_ok ( const void __user * ptr , unsigned long size )
{
2022-02-11 21:42:45 +01:00
unsigned long limit = TASK_SIZE_MAX ;
uaccess: generalize access_ok()
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]
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Stafford Horne <shorne@gmail.com>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
2022-02-15 17:55:04 +01:00
unsigned long addr = ( unsigned long ) ptr ;
if ( IS_ENABLED ( CONFIG_ALTERNATE_USER_ADDRESS_SPACE ) | |
! IS_ENABLED ( CONFIG_MMU ) )
return true ;
return ( size < = limit ) & & ( addr < = ( limit - size ) ) ;
}
# endif
# ifndef access_ok
# define access_ok(addr, size) likely(__access_ok(addr, size))
# endif
# endif
