From 6c1aca3e2d408ef4874bd882a7f0e2cd944bbf09 Mon Sep 17 00:00:00 2001 From: Alan Modra Date: Wed, 1 Apr 2015 19:19:27 +1030 Subject: [PATCH] Start of relro segment adjustment Adjusting the start of the relro segment in order to make it end exactly on a page boundary runs into difficulties when sections in the relro segment are aligned; Adjusting the start by (next_page - end) sometimes results in more than that adjustment occurring at the end, overrunning the page boundary. So when that occurs we try a new lower start position by masking the adjusted start with the maximum section alignment. However, we didn't consider that this masked start address may in fact be before the initial relro base, which is silly since that can only increase padding at the relro end. I've also moved some calculations closer to where they are used, and comments closer to the relevant statements. * ldlang.c (lang_size_sections): When alignment of sections results in relro base adjustment being too large, don't go lower than the initial value. * ldexp.c (fold_binary ): Comment. * scripttempl/elf.sc (DATA_SEGMENT_ALIGN): Omit SEGMENT_SIZE alignment when SEGMENT_SIZE is the same as MAXPAGESIZE. --- ld/ChangeLog | 9 +++++++++ ld/ldexp.c | 2 ++ ld/ldlang.c | 33 +++++++++++++++++---------------- ld/scripttempl/elf.sc | 6 +++++- 4 files changed, 33 insertions(+), 17 deletions(-) diff --git a/ld/ChangeLog b/ld/ChangeLog index 6b929aac24d..b8c506f2cf2 100644 --- a/ld/ChangeLog +++ b/ld/ChangeLog @@ -1,3 +1,12 @@ +2015-04-01 Alan Modra + + * ldlang.c (lang_size_sections): When alignment of sections + results in relro base adjustment being too large, don't go lower + than the initial value. + * ldexp.c (fold_binary ): Comment. + * scripttempl/elf.sc (DATA_SEGMENT_ALIGN): Omit SEGMENT_SIZE + alignment when SEGMENT_SIZE is the same as MAXPAGESIZE. + 2015-04-01 Alan Modra * emultempl/elf32.em (gld${EMULATION_NAME}_before_allocation): Don't diff --git a/ld/ldexp.c b/ld/ldexp.c index ac66cc02aef..9cd9e29d813 100644 --- a/ld/ldexp.c +++ b/ld/ldexp.c @@ -588,6 +588,8 @@ fold_binary (etree_type *tree) break; case DATA_SEGMENT_RELRO_END: + /* Operands swapped! DATA_SEGMENT_RELRO_END(offset,exp) + has offset in expld.result and exp in lhs. */ expld.dataseg.relro = exp_dataseg_relro_end; if (expld.phase == lang_first_phase_enum || expld.section != bfd_abs_section_ptr) diff --git a/ld/ldlang.c b/ld/ldlang.c index 888082147a1..13e7b1a3b99 100644 --- a/ld/ldlang.c +++ b/ld/ldlang.c @@ -5382,20 +5382,20 @@ lang_size_sections (bfd_boolean *relax, bfd_boolean check_regions) if (expld.dataseg.phase == exp_dataseg_end_seen && link_info.relro && expld.dataseg.relro_end) { - /* If DATA_SEGMENT_ALIGN DATA_SEGMENT_RELRO_END pair was seen, try - to put expld.dataseg.relro_end on a (common) page boundary. */ - bfd_vma min_base, relro_end, maxpage; + bfd_vma initial_base, min_base, relro_end, maxpage; expld.dataseg.phase = exp_dataseg_relro_adjust; maxpage = expld.dataseg.maxpagesize; - /* MIN_BASE is the absolute minimum address we are allowed to start the - read-write segment (byte before will be mapped read-only). */ - min_base = (expld.dataseg.min_base + maxpage - 1) & ~(maxpage - 1); + initial_base = expld.dataseg.base; + /* Try to put expld.dataseg.relro_end on a (common) page boundary. */ expld.dataseg.base += (-expld.dataseg.relro_end & (expld.dataseg.pagesize - 1)); /* Compute the expected PT_GNU_RELRO segment end. */ relro_end = ((expld.dataseg.relro_end + expld.dataseg.pagesize - 1) & ~(expld.dataseg.pagesize - 1)); + /* MIN_BASE is the absolute minimum address we are allowed to start the + read-write segment (byte before will be mapped read-only). */ + min_base = (expld.dataseg.min_base + maxpage - 1) & ~(maxpage - 1); if (min_base + maxpage < expld.dataseg.base) { expld.dataseg.base -= maxpage; @@ -5420,16 +5420,17 @@ lang_size_sections (bfd_boolean *relax, bfd_boolean check_regions) && sec->alignment_power > max_alignment_power) max_alignment_power = sec->alignment_power; - if (((bfd_vma) 1 << max_alignment_power) < expld.dataseg.pagesize) - { - /* Aligning the adjusted base guarantees the padding - between sections won't change. This is better than - simply subtracting 1 << max_alignment_power which is - what we used to do here. */ - expld.dataseg.base &= ~((1 << max_alignment_power) - 1); - lang_reset_memory_regions (); - one_lang_size_sections_pass (relax, check_regions); - } + /* Aligning the adjusted base guarantees the padding + between sections won't change. This is better than + simply subtracting 1 << max_alignment_power which is + what we used to do here. */ + expld.dataseg.base &= ~((1 << max_alignment_power) - 1); + /* It doesn't make much sense to go lower than the initial + base. That can only increase padding. */ + if (expld.dataseg.base < initial_base) + expld.dataseg.base = initial_base; + lang_reset_memory_regions (); + one_lang_size_sections_pass (relax, check_regions); } link_info.relro_start = expld.dataseg.base; link_info.relro_end = expld.dataseg.relro_end; diff --git a/ld/scripttempl/elf.sc b/ld/scripttempl/elf.sc index c9c80b0cc3e..b4f52eba4af 100644 --- a/ld/scripttempl/elf.sc +++ b/ld/scripttempl/elf.sc @@ -128,7 +128,11 @@ DATA_SEGMENT_ALIGN="ALIGN(${SEGMENT_SIZE}) + (. & (${MAXPAGESIZE} - 1))" DATA_SEGMENT_RELRO_END="" DATA_SEGMENT_END="" if test -n "${COMMONPAGESIZE}"; then - DATA_SEGMENT_ALIGN="ALIGN (${SEGMENT_SIZE}) - ((${MAXPAGESIZE} - .) & (${MAXPAGESIZE} - 1)); . = DATA_SEGMENT_ALIGN (${MAXPAGESIZE}, ${COMMONPAGESIZE})" + if test "${SEGMENT_SIZE}" != "${MAXPAGESIZE}"; then + DATA_SEGMENT_ALIGN="ALIGN (${SEGMENT_SIZE}) - ((${MAXPAGESIZE} - .) & (${MAXPAGESIZE} - 1)); . = DATA_SEGMENT_ALIGN (${MAXPAGESIZE}, ${COMMONPAGESIZE})" + else + DATA_SEGMENT_ALIGN="DATA_SEGMENT_ALIGN (${MAXPAGESIZE}, ${COMMONPAGESIZE})" + fi DATA_SEGMENT_END=". = DATA_SEGMENT_END (.);" DATA_SEGMENT_RELRO_END=". = DATA_SEGMENT_RELRO_END (${SEPARATE_GOTPLT-0}, .);" fi -- 2.30.2