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Subject[PATCH 3/3] binfmt_elf: Search an unmapped area with total_size but not map the whole image
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In elf_map(), we can search an unmapped area for the whole image of dynamic
loader with total_size, then map the first PT_LOAD segment with its own size.
But not map the while image, then unmap the remainder at the end.

And also update the code comment in elf_map() accordingly.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
fs/binfmt_elf.c | 25 ++++++++++++++-----------
1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d7a8a53a6f18..bebb9f2c934e 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -357,20 +357,23 @@ static unsigned long elf_map(struct file *filep, unsigned long addr,
return addr;

/*
- * total_size is the size of the ELF (interpreter) image.
- * The _first_ mmap needs to know the full size, otherwise
- * randomization might put this image into an overlapping
- * position with the ELF binary image. (since size < total_size)
- * So we first map the 'big' image - and unmap the remainder at
- * the end. (which unmap is needed for ELF images with holes.)
+ * total_size is the size of the ELF (interpreter) image if non-zero.
+ * It gets value either in load_elf_interp(), or in load_elf_binary()
+ * for "./ld.so someprog" testing. The _first_ mmap needs to know the
+ * full size, otherwise the first PT_LOAD segment is mapped below
+ * mm->mmap_base, the subsequent PT_LOAD segment(s) end up being mapped
+ * above mm->mmap_base into the area that is supposed to be the "gap"
+ * between the stack and the binary. So we search an unmapped area of
+ * total_size big, then use the found address as hint to do mmap.
*/
if (total_size) {
total_size = ELF_PAGEALIGN(total_size);
- map_addr = vm_mmap(filep, addr, total_size, prot, flags, off);
- if (!BAD_ADDR(map_addr))
- vm_munmap(map_addr+size, total_size-size);
- } else
- map_addr = vm_mmap(filep, addr, size, prot, flags, off);
+ addr = get_unmapped_area(file, addr, total_size, off, flags);
+ if (offset_in_page(addr))
+ return addr;
+ }
+
+ map_addr = vm_mmap(filep, addr, size, prot, flags, off);

return(map_addr);
}
--
2.5.5
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