On 10.03.23 18:16, Nils Hartmann wrote:
Hey,
I have a rather simple question about the MAP_SHARED_VALIDATE flag in mmap.
When used without a file pointer, EINVAL is returned. Is there a reason for this?
You mean, using it with shared anonymous memory? (MAP_SHARED|MAP_ANON)
I assume you mean "file descriptor" not "file pointer".
I researched a bit but could not find anything. I attached a simple patch that adds MAP_SHARE_VALIDATE to the flags switch and checks for invalid flags.
The only reason MAP_SHARED_VALIDATE was introduced was due to MAP_SYNC,
only required for DAX. DAX does not apply to shared anonymous memory.
I guess nobody cared/cares.
Question is if we want to update the implementation (there has to be a
good reason IMHO) or simply update the man page, stating that
MAP_SHARED_VALIDATE is not supported for MAP_ANON.
Signed-off-by: Nils Hartmann <nils1hartmann@xxxxxxxxx>
---
mm/mmap.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 740b54be3..fd7db51af 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1196,6 +1196,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
{
struct mm_struct *mm = current->mm;
vm_flags_t vm_flags;
+ unsigned long flags_mask;
int pkey = 0;
validate_mm(mm);
@@ -1266,14 +1267,14 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (mlock_future_check(mm, vm_flags, len))
return -EAGAIN;
+ flags_mask = LEGACY_MAP_MASK;
if (file) {
struct inode *inode = file_inode(file);
- unsigned long flags_mask;
if (!file_mmap_ok(file, inode, pgoff, len))
return -EOVERFLOW;
- flags_mask = LEGACY_MAP_MASK | file->f_op->mmap_supported_flags;
+ flags_mask |= file->f_op->mmap_supported_flags;
switch (flags & MAP_TYPE) {
case MAP_SHARED:
@@ -1327,6 +1328,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
}
} else {
switch (flags & MAP_TYPE) {
+ case MAP_SHARED_VALIDATE:
+ if (flags & ~flags_mask)
+ return -EOPNOTSUPP;
+ fallthrough;
case MAP_SHARED:
if (vm_flags & (VM_GROWSDOWN|VM_GROWSUP))
return -EINVAL;
--
Thanks,
David / dhildenb
