From patchwork Sat Nov 25 16:39:13 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "H.J. Lu" X-Patchwork-Id: 24528 Received: (qmail 127864 invoked by alias); 25 Nov 2017 16:39:18 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 127845 invoked by uid 89); 25 Nov 2017 16:39:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-25.0 required=5.0 tests=AWL, BAYES_00, FREEMAIL_FROM, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KB_WAM_FROM_NAME_SINGLEWORD, RCVD_IN_DNSWL_NONE, SPF_PASS autolearn=ham version=3.3.2 spammy= X-HELO: mail-ot0-f175.google.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=LyXwdqsbdtR4FkG8PTDGwr9kBv23ekhmv3szMibdGok=; b=fK0oh2b3EAPxvV4dUARaZtCqfjAVFeqBQVD176Ma6/iN7KzVNKAZCR+lT7Om+m1peq NoBHJbRQUVqXKu0gIQzTsa8052op+XBBbffdFxfBjabPL5ICwWNcQomKeCeOUG2e3Kfw ntxvOhKYraFrfvMVk7L3ZLVrdUqZ+yq7USYDbB5vTFwmIkRMwvBx8yP9OFtNbAVIF5oR pLZY83JsOksSLLzZ30qHg+mcONBlY0ufOt0HGR2MFH7g4cNh4ypYr3hbJGPIJnVyLvcs mgrRHGhbPx3Og1cR7pD6mC0CJC1qx4wIysry0vYKZsvi1+h7BlMeNE8YpAS5mLvLDBJY Vy9Q== X-Gm-Message-State: AJaThX7c/5x5a38WsW8yyjJJ9E7QOkzl80s8JNnFw5cIl6mf/yeuiegb JXQWqFzMTp8OKb3fbbRR+noMB0p6SdCwv2vkrI493Q== X-Google-Smtp-Source: AGs4zMY9KLl44UBbLoIMdZTKbsxKT12xnh3JhfQhMvZq31FAUzMJUkyNURUD29xN8H+o3zAe0voNHnBk7ADBHdZZlKc= X-Received: by 10.157.9.196 with SMTP id 4mr23609241otz.173.1511627953647; Sat, 25 Nov 2017 08:39:13 -0800 (PST) MIME-Version: 1.0 In-Reply-To: References: From: "H.J. Lu" Date: Sat, 25 Nov 2017 08:39:13 -0800 Message-ID: Subject: Re: [PATCH] Properly compute offsets of note descriptor and next note [BZ #22370] To: Andreas Schwab Cc: GNU C Library On Fri, Nov 24, 2017 at 6:45 AM, H.J. Lu wrote: > On Mon, Nov 20, 2017 at 5:04 AM, H.J. Lu wrote: >> On Thu, Nov 16, 2017 at 5:24 AM, H.J. Lu wrote: >>> On Wed, Nov 15, 2017 at 3:03 PM, H.J. Lu wrote: >>>> On Sun, Nov 12, 2017 at 8:03 AM, Andreas Schwab wrote: >>>>> On Nov 12 2017, "H.J. Lu" wrote: >>>>> >>>>>> Data after Elf64_Nhdr is the "name" field which is a 4-byte string, "GNU". >>>>>> There is no misalignment. >>>>> >>>>> That's not what your patch does. You are aligning both the name length >>>>> and the data length to a 8 byte boundary, making the note size >>>>> unaligned. >>>>> >>>> >>>> You are right. Both glibc and binutils get this wrong. I opened a >>>> binutils bug: >>>> >>>> https://sourceware.org/bugzilla/show_bug.cgi?id=22444 >>>> >>>> I will fix it first and take care of glibc next. >>>> >>> >>> Here is the glibc path. >>> >>> Any comments? >>> >> >> Any comments or objections? >> > > I updated Linux Extensions to gABI to clarify alignments of NOTE section > and segments: > > https://sourceware.org/ml/gnu-gabi/2017-q4/msg00003.html > > I will check it in next week. > Here is the updated patch I will check in next week. It added: + /* NB: Some PT_NOTE segment may have alignment value of 0 + or 1. gABI specifies that PT_NOTE segments should be + aligned to 4 bytes in 32-bit objects and to 8 bytes in + 64-bit objects. As a Linux extension, we also support + 4 byte alignment in 64-bit objects. If p_align is less + than 4, we treate alignment as 4 bytes. */ + ElfW(Addr) align = phdr[i].p_align; + if (align < 4) + align = 4; to prevent infinite loop with incorrect segment alignment. From b7cfacca88269901546529445f0bb757107984b4 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Tue, 31 Oct 2017 04:51:41 -0700 Subject: [PATCH] Properly compute offsets of note descriptor and next note [BZ #22370] A note header has 3 4-bytes fields, followed by note name and note descriptor. According to gABI, in a note entry, the note name field, not note name size, is padded for the note descriptor. And the note descriptor field, not note descriptor size, is padded for the next note entry. Notes are aligned to 4 bytes in 32-bit objects and 8 bytes in 64-bit objects. For all GNU notes, the name is "GNU" which is 4 bytes. They have the same format in the first 16 bytes in both 32-bit and 64-bit objects. They differ by note descriptor size and note type. So far, .note.ABI-tag and .note.gnu.build-id notes are always aligned to 4 bytes. The exsting codes compute the note size by aligning the note name size and note descriptor size to 4 bytes. It happens to produce the same value as the actual note size by luck since the name size is 4 and offset of the note descriptor is 16. But it will produce the wrong size when note alignment is 8 bytes in 64-bit objects. This patch defines ELF_NOTE_DESC_OFFSET and ELF_NOTE_NEXT_OFFSET to properly compute offsets of note descriptor and next note. It uses alignment of PT_NOTE segment to support both 4-byte and 8-byte note alignments in 64-bit objects. To handle PT_NOTE segments with incorrect alignment, which may lead to an infinite loop, if segment alignment is less than 4, we treate alignment as 4 bytes. [BZ #22370] * elf/dl-hwcaps.c (ROUND): Removed. (_dl_important_hwcaps): Replace ROUND with ELF_NOTE_DESC_OFFSET and ELF_NOTE_NEXT_OFFSET. * elf/dl-load.c (ROUND): Removed. (open_verify): Replace ROUND with ELF_NOTE_NEXT_OFFSET. * elf/readelflib.c (ROUND): Removed. (process_elf_file): Replace ROUND with ELF_NOTE_NEXT_OFFSET. * include/elf.h [!_ISOMAC]: Include . [!_ISOMAC] (ELF_NOTE_DESC_OFFSET): New. [!_ISOMAC] (ELF_NOTE_NEXT_OFFSET): Likewise. --- elf/dl-hwcaps.c | 21 +++++++++++++++------ elf/dl-load.c | 16 ++++++++++++---- elf/readelflib.c | 16 ++++++++++++---- include/elf.h | 16 ++++++++++++++-- 4 files changed, 53 insertions(+), 16 deletions(-) diff --git a/elf/dl-hwcaps.c b/elf/dl-hwcaps.c index 92f2eb45ce..b5f126b060 100644 --- a/elf/dl-hwcaps.c +++ b/elf/dl-hwcaps.c @@ -67,6 +67,15 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz, { const ElfW(Addr) start = (phdr[i].p_vaddr + GLRO(dl_sysinfo_map)->l_addr); + /* NB: Some PT_NOTE segment may have alignment value of 0 + or 1. gABI specifies that PT_NOTE segments should be + aligned to 4 bytes in 32-bit objects and to 8 bytes in + 64-bit objects. As a Linux extension, we also support + 4 byte alignment in 64-bit objects. If p_align is less + than 4, we treate alignment as 4 bytes. */ + ElfW(Addr) align = phdr[i].p_align; + if (align < 4) + align = 4; /* The standard ELF note layout is exactly as the anonymous struct. The next element is a variable length vendor name of length VENDORLEN (with a real length rounded to ElfW(Word)), followed @@ -80,7 +89,6 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz, } *note = (const void *) start; while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz) { -#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word))) /* The layout of the type 2, vendor "GNU" note is as follows: .long .long (as mask >> _DL_FIRST_EXTRA). @@ -91,17 +99,18 @@ _dl_important_hwcaps (const char *platform, size_t platform_len, size_t *sz, && !memcmp ((note + 1), "GNU", sizeof "GNU") && note->datalen > 2 * sizeof (ElfW(Word)) + 2) { - const ElfW(Word) *p = ((const void *) (note + 1) - + ROUND (sizeof "GNU")); + const ElfW(Word) *p + = ((const void *) note + + ELF_NOTE_DESC_OFFSET (sizeof "GNU", align)); cnt += *p++; ++p; /* Skip mask word. */ dsocaps = (const char *) p; /* Pseudo-string "name" */ dsocapslen = note->datalen - sizeof *p * 2; break; } - note = ((const void *) (note + 1) - + ROUND (note->vendorlen) + ROUND (note->datalen)); -#undef ROUND + note = ((const void *) note + + ELF_NOTE_NEXT_OFFSET (note->vendorlen, + note->datalen, align)); } if (dsocaps != NULL) break; diff --git a/elf/dl-load.c b/elf/dl-load.c index 1220183ce2..51a590a03a 100644 --- a/elf/dl-load.c +++ b/elf/dl-load.c @@ -1683,6 +1683,15 @@ open_verify (const char *name, int fd, if (ph->p_type == PT_NOTE && ph->p_filesz >= 32 && ph->p_align >= 4) { ElfW(Addr) size = ph->p_filesz; + /* NB: Some PT_NOTE segment may have alignment value of 0 + or 1. gABI specifies that PT_NOTE segments should be + aligned to 4 bytes in 32-bit objects and to 8 bytes in + 64-bit objects. As a Linux extension, we also support + 4 byte alignment in 64-bit objects. If p_align is less + than 4, we treate alignment as 4 bytes. */ + ElfW(Addr) align = ph->p_align; + if (align < 4) + align = 4; if (ph->p_offset + size <= (size_t) fbp->len) abi_note = (void *) (fbp->buf + ph->p_offset); @@ -1696,10 +1705,9 @@ open_verify (const char *name, int fd, while (memcmp (abi_note, &expected_note, sizeof (expected_note))) { -#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word))) - ElfW(Addr) note_size = 3 * sizeof (ElfW(Word)) - + ROUND (abi_note[0]) - + ROUND (abi_note[1]); + ElfW(Addr) note_size + = ELF_NOTE_NEXT_OFFSET (abi_note[0], abi_note[1], + align); if (size - 32 < note_size) { diff --git a/elf/readelflib.c b/elf/readelflib.c index 9ad56dcc34..4872f809e3 100644 --- a/elf/readelflib.c +++ b/elf/readelflib.c @@ -131,15 +131,23 @@ process_elf_file (const char *file_name, const char *lib, int *flag, ElfW(Word) *abi_note = (ElfW(Word) *) (file_contents + segment->p_offset); ElfW(Addr) size = segment->p_filesz; + /* NB: Some PT_NOTE segment may have alignment value of 0 + or 1. gABI specifies that PT_NOTE segments should be + aligned to 4 bytes in 32-bit objects and to 8 bytes in + 64-bit objects. As a Linux extension, we also support + 4 byte alignment in 64-bit objects. If p_align is less + than 4, we treate alignment as 4 bytes. */ + ElfW(Addr) align = segment->p_align; + if (align < 4) + align = 4; while (abi_note [0] != 4 || abi_note [1] != 16 || abi_note [2] != 1 || memcmp (abi_note + 3, "GNU", 4) != 0) { -#define ROUND(len) (((len) + sizeof (ElfW(Word)) - 1) & -sizeof (ElfW(Word))) - ElfW(Addr) note_size = 3 * sizeof (ElfW(Word)) - + ROUND (abi_note[0]) - + ROUND (abi_note[1]); + ElfW(Addr) note_size + = ELF_NOTE_NEXT_OFFSET (abi_note[0], abi_note[1], + align); if (size - 32 < note_size || note_size == 0) { diff --git a/include/elf.h b/include/elf.h index f06a33f256..ab76aafb1e 100644 --- a/include/elf.h +++ b/include/elf.h @@ -1,7 +1,19 @@ #ifndef _ELF_H #include -# ifndef _ISOMAC +#ifndef _ISOMAC + +# include + +/* Compute the offset of the note descriptor from size of note entry's + owner string and note alignment. */ +# define ELF_NOTE_DESC_OFFSET(namesz, align) \ + ALIGN_UP (sizeof (ElfW(Nhdr)) + (namesz), (align)) + +/* Compute the offset of the next note entry from size of note entry's + owner string, size of the note descriptor and note alignment. */ +# define ELF_NOTE_NEXT_OFFSET(namesz, descsz, align) \ + ALIGN_UP (ELF_NOTE_DESC_OFFSET ((namesz), (align)) + (descsz), (align)) /* Some information which is not meant for the public and therefore not in . */ @@ -13,5 +25,5 @@ (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \ | DF_1_ORIGIN | DF_1_NODEFLIB) -# endif /* !_ISOMAC */ +#endif /* !_ISOMAC */ #endif /* elf.h */ -- 2.14.3