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

[PATCH] 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.

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!
 #

Reported-by Pavithra Prakash <pavrampu@linux.vnet.ibm.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
---
 fs/hugetlbfs/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 412f295acebe..428fd2f0e4c4 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -228,7 +228,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
 
 	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) {
@@ -240,7 +240,7 @@ 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 &&
+		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
 		    (!vma || addr + len <= vm_start_gap(vma)))
 			return addr;
 	}
-- 
2.43.5

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

[Kirill A . Shutemov]

On Fri, Jul 05, 2024 at 02:11:50AM -0500, Donet Tom wrote:
> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
> index 412f295acebe..428fd2f0e4c4 100644
> --- a/fs/hugetlbfs/inode.c
> +++ b/fs/hugetlbfs/inode.c
> @@ -228,7 +228,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>  
>  	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) {
> @@ -240,7 +240,7 @@ 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 &&
> +		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
>  		    (!vma || addr + len <= vm_start_gap(vma)))
>  			return addr;
>  	}

There's more difference with generic_get_unmapped_area() than what you are
fixing. I think we also need vm_end_gap() here.

Hugetlb code duplication is annoying.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

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

[Donet Tom]

On 7/5/24 17:53, Kirill A . Shutemov wrote:
> On Fri, Jul 05, 2024 at 02:11:50AM -0500, Donet Tom wrote:
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 412f295acebe..428fd2f0e4c4 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -228,7 +228,7 @@ generic_hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>>   
>>   	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) {
>> @@ -240,7 +240,7 @@ 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 &&
>> +		if (mmap_end - len >= addr && addr >= mmap_min_addr &&
>>   		    (!vma || addr + len <= vm_start_gap(vma)))
>>   			return addr;
>>   	}
> There's more difference with generic_get_unmapped_area() than what you are
> fixing. I think we also need vm_end_gap() here.
Thank you for your comment. I will add this change and send V2.

-Donet
>
> Hugetlb code duplication is annoying.
>