From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_MSPIKE_H2 autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 20078 invoked from network); 2 Aug 2022 19:17:02 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 2 Aug 2022 19:17:02 -0000 Received: (qmail 24248 invoked by uid 550); 2 Aug 2022 19:16:59 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 24213 invoked from network); 2 Aug 2022 19:16:58 -0000 Date: Tue, 2 Aug 2022 15:16:46 -0400 From: Rich Felker To: Fangrui Song Cc: musl@lists.openwall.com Message-ID: <20220802191645.GT7074@brightrain.aerifal.cx> References: <20220606061633.539208-1-i@maskray.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220606061633.539208-1-i@maskray.me> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [PATCH] ldso: support DT_RELR relative relocation format On Sun, Jun 05, 2022 at 11:16:33PM -0700, Fangrui Song wrote: > this resolves DT_RELR relocations in non-ldso objects. > > generic-abi pre-standard for DT_RELR: > https://groups.google.com/g/generic-abi/c/bX460iggiKg > FreeBSD rtld added DT_RELR support in 2021-08. > glibc added DT_RELR support in 2022-04. > > Since ld.lld 7, --pack-dyn-relocs=relr can generate DT_RELR. > Since binutils 2.38, GNU ld's x86 and powerpc64 ports supports -z > pack-relative-relocs to generate DT_RELR. ld.lld 15 also has the option. > > --- > Changes from https://www.openwall.com/lists/musl/2019/03/06/3 > * rename some variables > * decode_vec: add `if (v[0] < 8*sizeof(long))` > --- > include/elf.h | 8 ++++++-- > ldso/dynlink.c | 20 +++++++++++++++++++- > src/internal/dynlink.h | 2 +- > 3 files changed, 26 insertions(+), 4 deletions(-) > > diff --git a/include/elf.h b/include/elf.h > index 86e2f0bb..9e980a29 100644 > --- a/include/elf.h > +++ b/include/elf.h > @@ -385,7 +385,8 @@ typedef struct { > #define SHT_PREINIT_ARRAY 16 > #define SHT_GROUP 17 > #define SHT_SYMTAB_SHNDX 18 > -#define SHT_NUM 19 > +#define SHT_RELR 19 > +#define SHT_NUM 20 > #define SHT_LOOS 0x60000000 > #define SHT_GNU_ATTRIBUTES 0x6ffffff5 > #define SHT_GNU_HASH 0x6ffffff6 > @@ -754,7 +755,10 @@ typedef struct { > #define DT_PREINIT_ARRAY 32 > #define DT_PREINIT_ARRAYSZ 33 > #define DT_SYMTAB_SHNDX 34 > -#define DT_NUM 35 > +#define DT_RELRSZ 35 > +#define DT_RELR 36 > +#define DT_RELRENT 37 > +#define DT_NUM 38 > #define DT_LOOS 0x6000000d > #define DT_HIOS 0x6ffff000 > #define DT_LOPROC 0x70000000 > diff --git a/ldso/dynlink.c b/ldso/dynlink.c > index 5b9c8be4..a50ef00a 100644 > --- a/ldso/dynlink.c > +++ b/ldso/dynlink.c > @@ -208,7 +208,8 @@ static void decode_vec(size_t *v, size_t *a, size_t cnt) > size_t i; > for (i=0; i for (; v[0]; v+=2) if (v[0]-1 - a[0] |= 1UL< + if (v[0] < 8*sizeof(long)) > + a[0] |= 1UL< a[v[0]] = v[1]; > } > } > @@ -513,6 +514,22 @@ static void do_relocs(struct dso *dso, size_t *rel, size_t rel_size, size_t stri > } > } > > +static void do_relr_relocs(struct dso *dso, size_t *relr, size_t relr_size) { > + unsigned char *base = dso->base; > + size_t *reloc_addr; > + for (; relr_size; relr++, relr_size-=sizeof(size_t)) > + if ((relr[0]&1) == 0) { > + reloc_addr = laddr(dso, relr[0]); > + *reloc_addr++ += (size_t)base; > + } else { > + int i = 0; > + for (size_t bitmap=relr[0]; (bitmap>>=1); i++) > + if (bitmap&1) > + reloc_addr[i] += (size_t)base; > + reloc_addr += 8*sizeof(size_t)-1; > + } > +} > + As written, this code is assuming !FDPIC, so should probably be conditional on that. However I think it can be written not to make this assumption, as: *reloc_addr = laddr(dso, *reloc_addr); reloc_addr++; instead of: *reloc_addr++ += base; and likewise in the second instance. The laddr() macro exists specifically to abstract translating "addresss in space of ELF image" to "address as mapped in memory" which I think is the intended semantic here. Is that correct? > static void redo_lazy_relocs() > { > struct dso *p = lazy_head, *next; > @@ -1355,6 +1372,7 @@ static void reloc_all(struct dso *p) > 2+(dyn[DT_PLTREL]==DT_RELA)); > do_relocs(p, laddr(p, dyn[DT_REL]), dyn[DT_RELSZ], 2); > do_relocs(p, laddr(p, dyn[DT_RELA]), dyn[DT_RELASZ], 3); > + do_relr_relocs(p, laddr(p, dyn[DT_RELR]), dyn[DT_RELRSZ]); > > if (head != &ldso && p->relro_start != p->relro_end && > mprotect(laddr(p, p->relro_start), p->relro_end-p->relro_start, PROT_READ) > diff --git a/src/internal/dynlink.h b/src/internal/dynlink.h > index 51c0639f..830354eb 100644 > --- a/src/internal/dynlink.h > +++ b/src/internal/dynlink.h > @@ -93,7 +93,7 @@ struct fdpic_dummy_loadmap { > #endif > > #define AUX_CNT 32 > -#define DYN_CNT 32 > +#define DYN_CNT 37 I was concerned about the decode_vec [0] slot bitmask usage, but you addressed that, and I've checked for other instances that might be wrong but couldn't find any, so I think it's okay. Rich