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([2804:431:c7cb:989a:419b:3fe6:8885:ab23]) by smtp.gmail.com with ESMTPSA id v15sm6173647otq.77.2022.01.18.09.48.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Jan 2022 09:49:00 -0800 (PST) Message-ID: <0a5eb87b-9a3c-6b3b-a82c-58e872e7e42f@linaro.org> Date: Tue, 18 Jan 2022 14:48:58 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v7 1/4] elf: Properly align all PT_LOAD segments [BZ #28676] Content-Language: en-US To: "H.J. Lu" , libc-alpha@sourceware.org Cc: Florian Weimer References: <20220103230433.1907240-1-hjl.tools@gmail.com> <20220103230433.1907240-2-hjl.tools@gmail.com> From: Adhemerval Zanella In-Reply-To: <20220103230433.1907240-2-hjl.tools@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.6 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 18 Jan 2022 17:49:03 -0000 On 03/01/2022 20:04, H.J. Lu wrote: > Linker may set p_align of a PT_LOAD segment larger than p_align of the > first PT_LOAD segment to satisfy a section alignment: > > Elf file type is DYN (Shared object file) > Entry point 0x0 > There are 10 program headers, starting at offset 64 > > Program Headers: > Type Offset VirtAddr PhysAddr > FileSiz MemSiz Flags Align > LOAD 0x0000000000000000 0x0000000000000000 0x0000000000000000 > 0x0000000000000834 0x0000000000000834 R E 0x1000 > LOAD 0x0000000000000e00 0x0000000000001e00 0x0000000000001e00 > 0x0000000000000230 0x0000000000000230 RW 0x1000 > LOAD 0x0000000000400000 0x0000000000400000 0x0000000000400000 > 0x0000000000000004 0x0000000000000008 RW 0x400000 > ... > > Section to Segment mapping: > Segment Sections... > 00 .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .plt.got .text .fini .rodata .eh_frame_hdr .eh_frame > 01 .init_array .fini_array .data.rel.ro .dynamic .got .got.plt > 02 .data .bss > > We should align the first PT_LOAD segment to the maximum p_align of all > PT_LOAD segments, similar to the kernel commit: > > commit ce81bb256a224259ab686742a6284930cbe4f1fa > Author: Chris Kennelly > Date: Thu Oct 15 20:12:32 2020 -0700 > > fs/binfmt_elf: use PT_LOAD p_align values for suitable start address > --- > elf/dl-load.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/elf/dl-load.c b/elf/dl-load.c > index ddc4295ef5..109bed3fb5 100644 > --- a/elf/dl-load.c > +++ b/elf/dl-load.c > @@ -1101,6 +1101,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, > size_t nloadcmds = 0; > bool has_holes = false; > bool empty_dynamic = false; > + ElfW(Addr) p_align_max = 0; > > /* The struct is initialized to zero so this is not necessary: > l->l_ld = 0; > @@ -1146,7 +1147,9 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, > c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize)); > c->dataend = ph->p_vaddr + ph->p_filesz; > c->allocend = ph->p_vaddr + ph->p_memsz; > - c->mapalign = ph->p_align; > + /* Remember the maximum p_align. */ > + if (ph->p_align > p_align_max) > + p_align_max = ph->p_align; > c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize)); > > /* Determine whether there is a gap between the last segment Kernel also skips non-power of two alignment as invalid, should we do the same to consider the max alignment? > @@ -1221,6 +1224,10 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, > goto lose; > } > > + /* Align all PT_LOAD segments to the maximum p_align. */ > + for (size_t i = 0; i < nloadcmds; i++) > + loadcmds[i].mapalign = p_align_max; > + > /* dlopen of an executable is not valid because it is not possible > to perform proper relocations, handle static TLS, or run the > ELF constructors. For PIE, the check needs the dynamic