Re: [PATCH v2] fs/hugetlbfs/inode.c: Ensure generic_hugetlb_get_unmapped_area() returns higher address than mmap_min_addr

[Kirill A . Shutemov]

On Tue, Jul 09, 2024 at 04:21:22AM -0500, Donet Tom wrote:
> generic_hugetlb_get_unmapped_area() was returning an address less
> than mmap_min_addr if the mmap argument addr, after alignment, was
> less than mmap_min_addr, causing mmap to fail.
> 
> This is because current generic_hugetlb_get_unmapped_area() code does
> not take into account mmap_min_addr.
> 
> This patch ensures that generic_hugetlb_get_unmapped_area() always returns
> an address that is greater than mmap_min_addr. Additionally, similar to
> generic_get_unmapped_area(), vm_end_gap() checks are included to ensure
> that the address is within the limit.

checks are included to maintain stack gap.

> 
> How to reproduce
> ================
> 
>  #include <stdio.h>
>  #include <stdlib.h>
>  #include <sys/mman.h>
>  #include <unistd.h>
> 
>  #define HUGEPAGE_SIZE (16 * 1024 * 1024)
> 
>  int main() {
> 
>     void *addr = mmap((void *)-1, HUGEPAGE_SIZE,
>                  PROT_READ | PROT_WRITE,
>                  MAP_SHARED | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
>     if (addr == MAP_FAILED) {
>         perror("mmap");
>         exit(EXIT_FAILURE);
>     }
> 
>     snprintf((char *)addr, HUGEPAGE_SIZE, "Hello, Huge Pages!");
> 
>     printf("%s\n", (char *)addr);
> 
>     if (munmap(addr, HUGEPAGE_SIZE) == -1) {
>         perror("munmap");
>         exit(EXIT_FAILURE);
>     }
> 
>     return 0;
>  }
> 
> Result without fix
> ==================
>  # cat /proc/meminfo |grep -i HugePages_Free
>  HugePages_Free:       20
>  # ./test
>  mmap: Permission denied
>  #
> 
> Result with fix
> ===============
>  # cat /proc/meminfo |grep -i HugePages_Free
>  HugePages_Free:       20
>  # ./test
>  Hello, Huge Pages!
>  #
> 
> V2:
> Added vm_end_gap() check.
> 
> V1:
> https://lore.kernel.org/all/20240705071150.84972-1-donettom@xxxxxxxxxxxxx/
> 
> Reported-by Pavithra Prakash <pavrampu@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Donet Tom <donettom@xxxxxxxxxxxxx>

Please use "hugetlbfs:" as subject prefix. No need to spell out full path.

Otherwise,

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov