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33f98a9798
The early malloc() and free() implementation in include/linux/decompress/mm.h
(which is also included by the static decompressors) is static. This is
fine when the only thing interested in using malloc() is the decompression
code, but the x86 early boot environment may use malloc() in a couple places,
leading to a potential collision when the static copies of the available
memory region ("malloc_ptr") gets reset to the global "free_mem_ptr" value.
As it happened, the existing usage pattern was accidentally safe because each
user did 1 malloc() and 1 free() before returning and were not nested:
extract_kernel() (misc.c)
choose_random_location() (kaslr.c)
mem_avoid_init()
handle_mem_options()
malloc()
...
free()
...
parse_elf() (misc.c)
malloc()
...
free()
Once the future FGKASLR series is added, however, it will insert
additional malloc() calls local to fgkaslr.c in the middle of
parse_elf()'s malloc()/free() pair:
parse_elf() (misc.c)
malloc()
if (...) {
layout_randomized_image(output, &ehdr, phdrs);
malloc() <- boom
...
else
layout_image(output, &ehdr, phdrs);
free()
To avoid collisions, there must be a single implementation of malloc().
Adjust include/linux/decompress/mm.h so that visibility can be
controlled, provide prototypes in misc.h, and implement the functions in
misc.c. This also results in a small size savings:
$ size vmlinux.before vmlinux.after
text data bss dec hex filename
8842314 468 178320 9021102 89a6ae vmlinux.before
8842240 468 178320 9021028 89a664 vmlinux.after
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20211013175742.1197608-4-keescook@chromium.org
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.