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

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

[Donet Tom]

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.

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@linux.ibm.com/

Reported-by Pavithra Prakash <pavrampu@linux.vnet.ibm.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
---
 fs/hugetlbfs/inode.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 412f295acebe..cdd8e53ddd19 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -222,13 +222,13 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 				  unsigned long flags)
 {
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
+	struct vm_area_struct *vma, *prev;
 	struct hstate *h = hstate_file(file);
 	const unsigned long mmap_end = arch_get_mmap_end(addr, len, flags);
 
 	if (len & ~huge_page_mask(h))
 		return -EINVAL;
-	if (len > TASK_SIZE)
+	if (len > mmap_end - mmap_min_addr)
 		return -ENOMEM;
 
 	if (flags & MAP_FIXED) {
@@ -239,9 +239,10 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 
 	if (addr) {
 		addr = ALIGN(addr, huge_page_size(h));
-		vma = find_vma(mm, addr);
-		if (mmap_end - len >= addr &&
-		    (!vma || addr + len <= vm_start_gap(vma)))
+		vma = find_vma_prev(mm, addr, &prev);
+		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
+		    (!vma || addr + len <= vm_start_gap(vma)) &&
+		    (!prev || addr >= vm_end_gap(prev)))
 			return addr;
 	}
 
-- 
2.43.5

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

[Oscar Salvador]

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.

Hi Donet,

jfyi: I am already working on other parts of the kernel to avoid hugetlb code
duplication vs mm core.
I am also working on getting rid of hugetlb-unmapped_area specific code
[1].
I still need to perform some more tests but looks promising
code-deletion-wise:

  arch/parisc/mm/hugetlbpage.c     |  23 -------
  arch/powerpc/mm/book3s64/slice.c |  49 ++++++++------
  arch/s390/mm/hugetlbpage.c       |  84 ------------------------
  arch/s390/mm/mmap.c              |  14 +++-
  arch/sparc/kernel/sys_sparc_32.c |  16 +++--
  arch/sparc/kernel/sys_sparc_64.c |  36 ++++++++---
  arch/sparc/mm/hugetlbpage.c      | 108 -------------------------------
  arch/x86/kernel/sys_x86_64.c     |  27 +++++---
  arch/x86/mm/hugetlbpage.c        | 100 ----------------------------
  fs/hugetlbfs/inode.c             |  97 ++-------------------------
  include/linux/hugetlb.h          |  10 +++
  mm/mmap.c                        |  25 ++++++-
  12 files changed, 139 insertions(+), 450 deletions(-)

I plan to post it in a day or two.

[1] https://github.com/leberus/linux/tree/hugetlb-unmapped-area


-- 
Oscar Salvador
SUSE Labs

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@linux.ibm.com/
> 
> Reported-by Pavithra Prakash <pavrampu@linux.vnet.ibm.com>
> Signed-off-by: Donet Tom <donettom@linux.ibm.com>

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

Otherwise,

Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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 15:26, Oscar Salvador 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.
> Hi Donet,
>
> jfyi: I am already working on other parts of the kernel to avoid hugetlb code
> duplication vs mm core.
> I am also working on getting rid of hugetlb-unmapped_area specific code
> [1].
> I still need to perform some more tests but looks promising
> code-deletion-wise:
>
>    arch/parisc/mm/hugetlbpage.c     |  23 -------
>    arch/powerpc/mm/book3s64/slice.c |  49 ++++++++------
>    arch/s390/mm/hugetlbpage.c       |  84 ------------------------
>    arch/s390/mm/mmap.c              |  14 +++-
>    arch/sparc/kernel/sys_sparc_32.c |  16 +++--
>    arch/sparc/kernel/sys_sparc_64.c |  36 ++++++++---
>    arch/sparc/mm/hugetlbpage.c      | 108 -------------------------------
>    arch/x86/kernel/sys_x86_64.c     |  27 +++++---
>    arch/x86/mm/hugetlbpage.c        | 100 ----------------------------
>    fs/hugetlbfs/inode.c             |  97 ++-------------------------
>    include/linux/hugetlb.h          |  10 +++
>    mm/mmap.c                        |  25 ++++++-
>    12 files changed, 139 insertions(+), 450 deletions(-)
>
> I plan to post it in a day or two.
>
> [1] https://github.com/leberus/linux/tree/hugetlb-unmapped-area
Thank you Oscar.

The issue I am trying to fix will also get fixed by this new changes right.
So should we drop my patch or should we continue it?

-Donet

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

[Oscar Salvador]

On Tue, Jul 09, 2024 at 07:14:38PM +0530, Donet Tom wrote:
> Thank you Oscar.

Hi Donet,

> The issue I am trying to fix will also get fixed by this new changes right.
> So should we drop my patch or should we continue it?

I would keep this patch as it is easier to backport as a small fixup.

Thanks

-- 
Oscar Salvador
SUSE Labs