71 lines
2.9 KiB
Diff
71 lines
2.9 KiB
Diff
commit 8eb2510d38226ce10a3a15109be948f052585106
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Author: Florian Weimer <fweimer@redhat.com>
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Date: Mon Jan 17 09:57:19 2022 +0100
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elf: Set l_contiguous to 1 for the main map in more cases
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l_contiguous was not initialized at all for the main map and
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always 0. This commit adds code to check if the LOAD segments
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are adjacent to each other, and sets l_contiguous accordingly.
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This helps _dl_find_object because it is more efficient if the
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main mapping is contiguous.
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Note that not all (PIE or non-PIE) binaries are contiguous in this
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way because BFD ld creates executables with LOAD holes:
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ELF LOAD segments creating holes in the process image on GNU/Linux
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https://sourceware.org/pipermail/binutils/2022-January/119082.html
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https://sourceware.org/bugzilla/show_bug.cgi?id=28743
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Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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diff --git a/elf/rtld.c b/elf/rtld.c
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index a47e105987d87add..d698a32ae120e887 100644
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--- a/elf/rtld.c
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+++ b/elf/rtld.c
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@@ -1147,6 +1147,22 @@ rtld_setup_main_map (struct link_map *main_map)
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main_map->l_map_start = ~0;
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/* And it was opened directly. */
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++main_map->l_direct_opencount;
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+ main_map->l_contiguous = 1;
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+
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+ /* A PT_LOAD segment at an unexpected address will clear the
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+ l_contiguous flag. The ELF specification says that PT_LOAD
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+ segments need to be sorted in in increasing order, but perhaps
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+ not all executables follow this requirement. Having l_contiguous
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+ equal to 1 is just an optimization, so the code below does not
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+ try to sort the segments in case they are unordered.
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+
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+ There is one corner case in which l_contiguous is not set to 1,
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+ but where it could be set: If a PIE (ET_DYN) binary is loaded by
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+ glibc itself (not the kernel), it is always contiguous due to the
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+ way the glibc loader works. However, the kernel loader may still
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+ create holes in this case, and the code here still uses 0
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+ conservatively for the glibc-loaded case, too. */
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+ ElfW(Addr) expected_load_address = 0;
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/* Scan the program header table for the dynamic section. */
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for (const ElfW(Phdr) *ph = phdr; ph < &phdr[phnum]; ++ph)
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@@ -1210,12 +1226,21 @@ rtld_setup_main_map (struct link_map *main_map)
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if (main_map->l_map_start > mapstart)
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main_map->l_map_start = mapstart;
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+ if (main_map->l_contiguous && expected_load_address != 0
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+ && expected_load_address != mapstart)
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+ main_map->l_contiguous = 0;
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+
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/* Also where it ends. */
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allocend = main_map->l_addr + ph->p_vaddr + ph->p_memsz;
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if (main_map->l_map_end < allocend)
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main_map->l_map_end = allocend;
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if ((ph->p_flags & PF_X) && allocend > main_map->l_text_end)
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main_map->l_text_end = allocend;
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+
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+ /* The next expected address is the page following this load
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+ segment. */
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+ expected_load_address = ((allocend + GLRO(dl_pagesize) - 1)
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+ & ~(GLRO(dl_pagesize) - 1));
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}
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break;
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