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 28058 invoked from network); 2 Aug 2022 20:18:00 -0000 Received: from second.openwall.net (193.110.157.125) by inbox.vuxu.org with ESMTPUTF8; 2 Aug 2022 20:18:00 -0000 Received: (qmail 15842 invoked by uid 550); 2 Aug 2022 20:17:57 -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 15808 invoked from network); 2 Aug 2022 20:17:56 -0000 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=bW5Wfz99bgE3Aup0GQFRAeQdu+lhHziyqHJZLpLwUWo=; b=TYBHVKsekD+5C41g68v9HVbTuMkYm2SVve3LWNYvjdm3d1H62p11TAKZ6sXTZh6xGb wUaf02zCo+3D5CaO3Si4eM66A53isVUrd8eaYnmlYQ9HvZq4pnIc8srlP/8MY7BRc2wq 2QiJLLvW8n4ScFmqut+rovQYUGkneQqSPIDQEE7ZzvLg4M0nO2vbvI6mKkiCCv8LNKYR 7U9O3oH5LYg4hXGKHhgL8jkp8btgDC32UwNvtfQmsB5JRtcWmK5weP2YYO4p+mAxtybX YRo3BZgFplQW0fxs22wS+2zM4saII6fb5UfPWCo+xoQ0j5M//qnTklicyzW2Xp90mkuk oieg== X-Gm-Message-State: AJIora/gXaS68Ovb+JxawGctrcFwhnxA2Hz9Axw/XalgRbT05yE1wsji odX2KSftmz4tzwUkACmmXGO0/nh5pnE= X-Google-Smtp-Source: AGRyM1sOfd3XH9VWUECofqC+Vzcur373SLVDqP75Id0bjOWtig5VzPyPrwAbFZDdl9olF3D6YvMVFw== X-Received: by 2002:a63:6b06:0:b0:41b:79cd:f364 with SMTP id g6-20020a636b06000000b0041b79cdf364mr18826378pgc.119.1659471463981; Tue, 02 Aug 2022 13:17:43 -0700 (PDT) Date: Tue, 2 Aug 2022 13:17:42 -0700 From: Fangrui Song To: musl@lists.openwall.com Message-ID: <20220802201742.nl77eqxwm3oemuqr@gmail.com> References: <20220606061633.539208-1-i@maskray.me> <20220802191645.GT7074@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20220802191645.GT7074@brightrain.aerifal.cx> Subject: Re: [musl] [PATCH] ldso: support DT_RELR relative relocation format On 2022-08-02, Rich Felker wrote: >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? I have to confess I don't know much about FDPIC (I merely read a little bit about "ARM FDPIC ABI" a while ago.) DT_RELR operations should resemble REL_RELATIVE for REL/RELA. The REL_RELATIVE code does *reloc_addr = (size_t)base + addend; so I think `*reloc_addr++ += (size_t)base;` is fine. >> 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