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* [glibc] hurd: Implement MAP_EXCL
@ 2023-07-02 23:38 Samuel Thibault
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From: Samuel Thibault @ 2023-07-02 23:38 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=27cb2bb93d611d772621e801bf85c8b2b4c8b598
commit 27cb2bb93d611d772621e801bf85c8b2b4c8b598
Author: Sergey Bugaev <bugaevc@gmail.com>
Date: Mon Jun 26 02:17:51 2023 +0300
hurd: Implement MAP_EXCL
MAP_FIXED is defined to silently replace any existing mappings at the
address range being mapped over. This, however, is a dangerous, and only
rarely desired behavior.
Various Unix systems provide replacements or additions to MAP_FIXED:
* SerenityOS and Linux provide MAP_FIXED_NOREPLACE. If the address space
already contains a mapping in the requested range, Linux returns
EEXIST. SerenityOS returns ENOMEM, however that is a bug, as the
MAP_FIXED_NOREPLACE implementation is intended to be compatible with
Linux.
* FreeBSD provides the MAP_EXCL flag that has to be used in combination
with MAP_FIXED. It returns EINVAL if the requested range already
contains existing mappings. This is directly analogous to the O_EXCL
flag in the open () call.
* DragonFly BSD, NetBSD, and OpenBSD provide MAP_TRYFIXED, but with
different semantics. DragonFly BSD returns ENOMEM if the requested
range already contains existing mappings. NetBSD does not return an
error, but instead creates the mapping at a different address if the
requested range contains mappings. OpenBSD behaves the same, but also
notes that this is the default behavior even without MAP_TRYFIXED
(which is the case on the Hurd too).
Since the Hurd leans closer to the BSD side, add MAP_EXCL as the primary
API to request the behavior of not replacing existing mappings. Declare
MAP_FIXED_NOREPLACE and MAP_TRYFIXED as aliases of (MAP_FIXED|MAP_EXCL),
so any existing software that checks for either of those macros will
pick them up automatically. For compatibility with Linux, return EEXIST
if a mapping already exists.
Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Message-Id: <20230625231751.404120-5-bugaevc@gmail.com>
Diff:
---
sysdeps/mach/hurd/bits/mman_ext.h | 7 ++++++-
sysdeps/mach/hurd/mmap.c | 26 +++++++++++++++++---------
2 files changed, 23 insertions(+), 10 deletions(-)
diff --git a/sysdeps/mach/hurd/bits/mman_ext.h b/sysdeps/mach/hurd/bits/mman_ext.h
index bbb94743e9..9658cdd658 100644
--- a/sysdeps/mach/hurd/bits/mman_ext.h
+++ b/sysdeps/mach/hurd/bits/mman_ext.h
@@ -22,5 +22,10 @@
#ifdef __USE_GNU
# define SHM_ANON ((const char *) 1)
-# define MAP_32BIT 0x1000
+
+# define MAP_32BIT 0x1000 /* Map in the lower 2 GB. */
+# define MAP_EXCL 0x4000 /* With MAP_FIXED, don't replace existing mappings. */
+
+# define MAP_TRYFIXED (MAP_FIXED | MAP_EXCL) /* BSD name. */
+# define MAP_FIXED_NOREPLACE (MAP_FIXED | MAP_EXCL) /* Linux name. */
#endif /* __USE_GNU */
diff --git a/sysdeps/mach/hurd/mmap.c b/sysdeps/mach/hurd/mmap.c
index 33672cf60a..20264a775b 100644
--- a/sysdeps/mach/hurd/mmap.c
+++ b/sysdeps/mach/hurd/mmap.c
@@ -46,6 +46,9 @@ __mmap (void *addr, size_t len, int prot, int flags, int fd, off_t offset)
if ((mapaddr & (__vm_page_size - 1)) || (offset & (__vm_page_size - 1)))
return (void *) (long int) __hurd_fail (EINVAL);
+ if ((flags & MAP_EXCL) && ! (flags & MAP_FIXED))
+ return (void *) (long int) __hurd_fail (EINVAL);
+
vmprot = VM_PROT_NONE;
if (prot & PROT_READ)
vmprot |= VM_PROT_READ;
@@ -156,15 +159,20 @@ __mmap (void *addr, size_t len, int prot, int flags, int fd, off_t offset)
{
if (err == KERN_NO_SPACE)
{
- /* XXX this is not atomic as it is in unix! */
- /* The region is already allocated; deallocate it first. */
- err = __vm_deallocate (__mach_task_self (), mapaddr, len);
- if (! err)
- err = __vm_map (__mach_task_self (),
- &mapaddr, (vm_size_t) len, mask,
- 0, memobj, (vm_offset_t) offset,
- copy, vmprot, max_vmprot,
- copy ? VM_INHERIT_COPY : VM_INHERIT_SHARE);
+ if (flags & MAP_EXCL)
+ err = EEXIST;
+ else
+ {
+ /* The region is already allocated; deallocate it first. */
+ /* XXX this is not atomic as it is in unix! */
+ err = __vm_deallocate (__mach_task_self (), mapaddr, len);
+ if (! err)
+ err = __vm_map (__mach_task_self (),
+ &mapaddr, (vm_size_t) len, mask,
+ 0, memobj, (vm_offset_t) offset,
+ copy, vmprot, max_vmprot,
+ copy ? VM_INHERIT_COPY : VM_INHERIT_SHARE);
+ }
}
}
else
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