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

[Donet Tom]

On 7/9/24 16:04, Kirill A . Shutemov wrote:
> 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.
Thank you. I will update and send  V3.

-Donet
> > 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>