linux-kernel - [PATCH] fs/hugetlbfs/inode.c: Ensure generic_hugetlb_get_unmapped_area() returns higher address than mmap_min

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Message-ID: <20240705071150.84972-1-donettom@linux.ibm.com>
Date: Fri,  5 Jul 2024 02:11:50 -0500
From: Donet Tom <donettom@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
        Muchun Song <muchun.song@...ux.dev>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Ritesh Harjani <ritesh.list@...il.com>,
        Mike Rapoport <rppt@...nel.org>, David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Tony Battersby <tonyb@...ernetics.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Donet Tom <donettom@...ux.ibm.com>
Subject: [PATCH] fs/hugetlbfs/inode.c: Ensure generic_hugetlb_get_unmapped_area() returns higher address than mmap_min_addr

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@...ux.vnet.ibm.com>
Signed-off-by: Donet Tom <donettom@...ux.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