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Subject[patch][resend] MAP_HUGETLB munmap fails with size not 2MB aligned
[Resending with proper CC list suggested by Andrew]

Calling munmap on a MAP_HUGETLB area, and a size which is not 2MB aligned,
causes munmap to fail. Tested on 3.13.x but tracking back to 3.2.x.
In do_munmap() we forcibly want a 4KB default page, and we wrongly
calculate the end of the map. Since the calculated end is within the end
address of the target vma, we try to do a split with an address right in
the middle of a huge page, which would fail with EINVAL.

Tentative (untested) patch and test case attached (be sure you have a few
huge pages available via /proc/sys/vm/nr_hugepages tinkering).


Signed-Off-By: Davide Libenzi <davidel@xmailserver.org>


- Davide


diff --git a/mm/mmap.c b/mm/mmap.c
index 7f85520..6dba257 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2528,10 +2528,6 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
if ((start & ~PAGE_MASK) || start > TASK_SIZE || len > TASK_SIZE-start)
return -EINVAL;

- len = PAGE_ALIGN(len);
- if (len == 0)
- return -EINVAL;
-
/* Find the first overlapping VMA */
vma = find_vma(mm, start);
if (!vma)
@@ -2539,6 +2535,16 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len)
prev = vma->vm_prev;
/* we have start < vma->vm_end */

+ if (likely(!is_vm_hugetlb_page(vma)))
+ len = PAGE_ALIGN(len);
+ else {
+ unsigned long hpage_size = huge_page_size(hstate_vma(vma));
+
+ len = ALIGN(len, hpage_size);
+ }
+ if (unlikely(len == 0))
+ return -EINVAL;
+
/* if it doesn't overlap, we have nothing.. */
end = start + len;
if (vma->vm_start >= end)



[hugebug.c]

#include <sys/mman.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

static void test(int flags, size_t size)
{
void* addr = mmap(NULL, size, PROT_READ | PROT_WRITE,
flags | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (addr == MAP_FAILED)
{
perror("mmap");
exit(1);
}
*(char*) addr = 17;
if (munmap(addr, size) != 0)
{
perror("munmap");
exit(1);
}
}
int main(int ac, const char** av)
{
static const size_t hugepage_size = 2 * 1024 * 1024;
printf("Testing normal pages with 2MB size ...\n");
test(0, hugepage_size);
printf("OK\n");

printf("Testing huge pages with 2MB size ...\n");
test(MAP_HUGETLB, hugepage_size);
printf("OK\n");


printf("Testing normal pages with 4KB byte size ...\n");
test(0, 4096);
printf("OK\n");

printf("Testing huge pages with 4KB byte size ...\n");
test(MAP_HUGETLB, 4096);
printf("OK\n");


printf("Testing normal pages with 1 byte size ...\n");
test(0, 1);
printf("OK\n");

printf("Testing huge pages with 1 byte size ...\n");
test(MAP_HUGETLB, 1);
printf("OK\n");

return 0;
}


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