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authorGiuseppe Musacchio <thatlemon@gmail.com>2020-12-17 11:17:40 +0100
committerLaurent Vivier <laurent@vivier.eu>2021-02-13 22:50:49 +0100
commit22d113b52f410d345c3a50a00d2eafa64138e427 (patch)
tree78b5d779be24a65456845042bc319252de3d7f03 /linux-user/elfload.c
parent78721301138114cf37fb179a6cf73a27c1b3a927 (diff)
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linux-user: Fix loading of BSS segments
Some ELF binaries encode the .bss section as an extension of the data ones by setting the segment p_memsz > p_filesz. Some other binaries take a different route and encode it as a stand-alone PT_LOAD segment with p_filesz = 0 and p_memsz > 0. Both the encodings are actually correct per ELF specification but the ELF loader had some troubles in handling the former: with the old logic it was very likely to get Qemu to crash in zero_bss when trying to access unmapped memory. zero_bss isn't meant to allocate whole zero-filled segments but to "complete" a previously mapped segment with the needed zero bits. The fix is pretty simple, if the segment is completely zero-filled we simply allocate one or more pages (according to p_memsz) and avoid calling zero_bss altogether. Signed-off-by: Giuseppe Musacchio <thatlemon@gmail.com> Message-Id: <c9106487-dc4d-120a-bd48-665b3c617287@gmail.com> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Diffstat (limited to 'linux-user/elfload.c')
-rw-r--r--linux-user/elfload.c30
1 files changed, 20 insertions, 10 deletions
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index a640507..f5bd407 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2805,14 +2805,16 @@ static void load_elf_image(const char *image_name, int image_fd,
vaddr = load_bias + eppnt->p_vaddr;
vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
vaddr_ps = TARGET_ELF_PAGESTART(vaddr);
- vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
+
+ vaddr_ef = vaddr + eppnt->p_filesz;
+ vaddr_em = vaddr + eppnt->p_memsz;
/*
- * Some segments may be completely empty without any backing file
- * segment, in that case just let zero_bss allocate an empty buffer
- * for it.
+ * Some segments may be completely empty, with a non-zero p_memsz
+ * but no backing file segment.
*/
if (eppnt->p_filesz != 0) {
+ vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_filesz + vaddr_po);
error = target_mmap(vaddr_ps, vaddr_len, elf_prot,
MAP_PRIVATE | MAP_FIXED,
image_fd, eppnt->p_offset - vaddr_po);
@@ -2820,14 +2822,22 @@ static void load_elf_image(const char *image_name, int image_fd,
if (error == -1) {
goto exit_mmap;
}
- }
- vaddr_ef = vaddr + eppnt->p_filesz;
- vaddr_em = vaddr + eppnt->p_memsz;
+ /*
+ * If the load segment requests extra zeros (e.g. bss), map it.
+ */
+ if (eppnt->p_filesz < eppnt->p_memsz) {
+ zero_bss(vaddr_ef, vaddr_em, elf_prot);
+ }
+ } else if (eppnt->p_memsz != 0) {
+ vaddr_len = TARGET_ELF_PAGELENGTH(eppnt->p_memsz + vaddr_po);
+ error = target_mmap(vaddr_ps, vaddr_len, elf_prot,
+ MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS,
+ -1, 0);
- /* If the load segment requests extra zeros (e.g. bss), map it. */
- if (vaddr_ef < vaddr_em) {
- zero_bss(vaddr_ef, vaddr_em, elf_prot);
+ if (error == -1) {
+ goto exit_mmap;
+ }
}
/* Find the full program boundaries. */