Date: Mon, 3 Sep 2012 15:46:42 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Svatopluk Kraus <onwahe@gmail.com> Cc: freebsd-current@freebsd.org Subject: Re: [patch] mmap() MAP_TEXT implementation (to use for shared libraries) Message-ID: <20120903124642.GI33100@deviant.kiev.zoral.com.ua> In-Reply-To: <CAFHCsPX6HrCXHA%2BS31Dz9QP8eiwbo21Vzju4K4paohciu2vPTw@mail.gmail.com> References: <CAFHCsPX6HrCXHA%2BS31Dz9QP8eiwbo21Vzju4K4paohciu2vPTw@mail.gmail.com>
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--q+qpHfi2NROeSQHU Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Sep 03, 2012 at 12:35:08PM +0200, Svatopluk Kraus wrote: > Hi, >=20 > I found out that while the running excecutables and a dynamic linker > are protected against writing (ETXTBSY), the loaded shared libraries > are not protected. The libraries are mapped by mmap() in dynamic > linker (rtld) and there is no way how to set VV_TEXT flag on the > libraries vnodes in mmap() code. >=20 > In linux compability code \compat\linux\linux_misc.c, linux_uselib() > sets VV_TEXT flags on a library vnode. In Solaris, MAP_TEXT flag > exists which informs mmap() that the mapped region will be used > primarily for executing instructions (for better MMU utilization). > With these on mind, I propose to implement MAP_TEXT option in mmap() > and in case that underlying object is a vnode, set VV_TEXT flag on it. >=20 > I already have implemented it and with rtld map_object() patch it > works fine for me (of course). The rtld patch looks easy, however I'm > not sure about mmap patch. >=20 > After some investigation, it looks that VV_TEXT once set on a vnode > remains set until last reference on the vnode is left. So, I don't > bother with VV_TEXT unset in munmap() to be consistent. The > executables and dynamic linker are activated in kernel, so VV_TEXT is > set before activation and cleared if something failed. Shared library > activation is done in dynamic linker (i.e., in userland). It's done in > steps and mmaping the library is one from them. So, I think that > VV_TEXT can be set in mmap() just after everything is finished > successfully. This is right, the object reference counter is also used as VV_TEXT counter. It is somewhat unaccurate, but in practice does not cause issues. >=20 > The patch itself is implemented in vm_mmap_vnode(). If I want to set > VV_TEXT flag on a vnode, I need an exclusive lock. In current code, > the exclusive lock flag is (mis)used as a flag for > vnode_pager_update_writecount() call. (I hope that I didn't miss > something.) So, the patch is bigger slightly. >=20 > I defined the MAP_TEXT flag in extented flags sections. However, I'm > feeling the relation to MAP_STACK flag, but not sure if and when > reserved flags (in other flags section) can be re-used. >=20 > Svata >=20 >=20 > Index: libexec/rtld-elf/map_object.c > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- libexec/rtld-elf/map_object.c (revision 239770) > +++ libexec/rtld-elf/map_object.c (working copy) > @@ -199,7 +199,8 @@ > data_prot =3D convert_prot(segs[i]->p_flags); > data_flags =3D convert_flags(segs[i]->p_flags) | MAP_FIXED; > if (mmap(data_addr, data_vlimit - data_vaddr, data_prot, > - data_flags | MAP_PREFAULT_READ, fd, data_offset) =3D=3D (caddr_t) -1)= { > + data_flags | MAP_PREFAULT_READ | MAP_TEXT, fd, data_offset) =3D=3D > + (caddr_t) -1) { I am not sure that we shall mark all segments mappings with MAP_TEXT. I understand the logic of the change, since we do not want data segment to be changed under us. Still, having MAP_TEXT for non-text segments looks strange. > _rtld_error("%s: mmap of data failed: %s", path, > rtld_strerror(errno)); > goto error1; > Index: sys/vm/vm_mmap.c > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- sys/vm/vm_mmap.c (revision 239770) > +++ sys/vm/vm_mmap.c (working copy) > @@ -1258,10 +1258,13 @@ > struct mount *mp; > struct ucred *cred; > int error, flags, locktype, vfslocked; > + int writeable_shared; >=20 > mp =3D vp->v_mount; > cred =3D td->td_ucred; > - if ((*maxprotp & VM_PROT_WRITE) && (*flagsp & MAP_SHARED)) > + flags =3D *flagsp; > + writeable_shared =3D ((*maxprotp & VM_PROT_WRITE) && (flags & MAP_SHARE= D)); > + if (writeable_shared || ((flags & MAP_TEXT) !=3D 0)) > locktype =3D LK_EXCLUSIVE; > else > locktype =3D LK_SHARED; > @@ -1271,7 +1274,6 @@ > return (error); > } > foff =3D *foffp; > - flags =3D *flagsp; > obj =3D vp->v_object; > if (vp->v_type =3D=3D VREG) { > /* > @@ -1294,7 +1296,7 @@ > return (error); > } > } > - if (locktype =3D=3D LK_EXCLUSIVE) { > + if (writeable_shared) { > *writecounted =3D TRUE; > vnode_pager_update_writecount(obj, 0, objsize); > } > @@ -1337,6 +1339,14 @@ > error =3D ENOMEM; > goto done; > } > + /* > + * If MAP_TEXT is announced, set VV_TEXT so no one can write > + * to the executable. > + */ > + if ((flags & MAP_TEXT) !=3D 0) { > + ASSERT_VOP_ELOCKED(vp, "vv_text"); > + vp->v_vflag |=3D VV_TEXT; > + } I do not think we want to set VV_TEXT for device vnodes. > *objp =3D obj; > *flagsp =3D flags; >=20 > Index: sys/sys/mman.h > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > --- sys/sys/mman.h (revision 239770) > +++ sys/sys/mman.h (working copy) > @@ -91,6 +91,7 @@ > */ > #define MAP_NOCORE 0x00020000 /* dont include these pages in a coredump= */ > #define MAP_PREFAULT_READ 0x00040000 /* prefault mapping for reading */ > +#define MAP_TEXT 0x00080000 /* map code segment */ > #endif /* __BSD_VISIBLE */ >=20 > #if __POSIX_VISIBLE >=3D 199309 > _______________________________________________ > freebsd-current@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-current > To unsubscribe, send any mail to "freebsd-current-unsubscribe@freebsd.org" --q+qpHfi2NROeSQHU Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAlBEprIACgkQC3+MBN1Mb4h5yACggbaWE+xAW3fsF8IXMohsHxtW pZwAmwb4i4Mgt/RHBLdM56PNcE3Qsxdk =a2Zn -----END PGP SIGNATURE----- --q+qpHfi2NROeSQHU--
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