From 27cb2bb93d611d772621e801bf85c8b2b4c8b598 Mon Sep 17 00:00:00 2001 From: Sergey Bugaev Date: Mon, 26 Jun 2023 02:17:51 +0300 Subject: 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 Message-Id: <20230625231751.404120-5-bugaevc@gmail.com> --- 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 -- cgit 1.4.1