Re: x86/kaslr: Expose and use the end of the physical memory address space

[Guenter Roeck <linux@roeck-us.net>]

On Wed, Aug 14, 2024 at 12:29:36AM +0200, Thomas Gleixner wrote:
> iounmap() on x86 occasionally fails to unmap because the provided valid
> ioremap address is not below high_memory. It turned out that this
> happens due to KASLR.
> 
[ ... ]
>  
> --- a/kernel/resource.c
> +++ b/kernel/resource.c
> @@ -1826,8 +1826,7 @@ static resource_size_t gfr_start(struct
>  	if (flags & GFR_DESCENDING) {
>  		resource_size_t end;
>  
> -		end = min_t(resource_size_t, base->end,
> -			    (1ULL << MAX_PHYSMEM_BITS) - 1);
> +		end = min_t(resource_size_t, base->end, PHYSMEM_END);
>  		return end - size + 1;
>  	}

When trying to build arm:allmodconfig or mips:allmodconfig (and probably
others):

Building arm:allmodconfig ... failed
--------------
Error log:
In file included from include/linux/ioport.h:15,
                 from kernel/resource.c:15:
kernel/resource.c: In function 'gfr_start':
include/linux/minmax.h:93:37: error: conversion from 'long long unsigned int' to 'resource_size_t' {aka 'unsigned int'} changes value from '18446744073709551615' to '4294967295' [-Werror=overflow]
   93 |         ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
      |                                     ^
include/linux/minmax.h:96:9: note: in expansion of macro '__cmp_once_unique'
   96 |         __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
      |         ^~~~~~~~~~~~~~~~~
include/linux/minmax.h:213:27: note: in expansion of macro '__cmp_once'
  213 | #define min_t(type, x, y) __cmp_once(min, type, x, y)
      |                           ^~~~~~~~~~
kernel/resource.c:1874:23: note: in expansion of macro 'min_t'
 1874 |                 end = min_t(resource_size_t, base->end, PHYSMEM_END);
      |                       ^~~~~
kernel/resource.c: In function 'gfr_continue':
include/linux/minmax.h:93:37: error: conversion from 'long long unsigned int' to 'resource_size_t' {aka 'unsigned int'} changes value from '18446744073709551615' to '4294967295' [-Werror=overflow]
   93 |         ({ type ux = (x); type uy = (y); __cmp(op, ux, uy); })
      |                                     ^
include/linux/minmax.h:96:9: note: in expansion of macro '__cmp_once_unique'
   96 |         __cmp_once_unique(op, type, x, y, __UNIQUE_ID(x_), __UNIQUE_ID(y_))
      |         ^~~~~~~~~~~~~~~~~
include/linux/minmax.h:213:27: note: in expansion of macro '__cmp_once'
  213 | #define min_t(type, x, y) __cmp_once(min, type, x, y)
      |                           ^~~~~~~~~~
kernel/resource.c:1891:24: note: in expansion of macro 'min_t'
 1891 |                addr <= min_t(resource_size_t, base->end, PHYSMEM_END);
      |                        ^~~~~

Guenter