From 33f98a9798f55fd77c36ce79d8cfa5329e55a789 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 13 Oct 2021 10:57:41 -0700 Subject: x86/boot/compressed: Avoid duplicate malloc() implementations 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 Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20211013175742.1197608-4-keescook@chromium.org --- arch/x86/boot/compressed/misc.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch/x86/boot/compressed/misc.c') diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c index 743f13ea25c1..a4339cb2d247 100644 --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -28,6 +28,9 @@ /* Macros used by the included decompressor code below. */ #define STATIC static +/* Define an externally visible malloc()/free(). */ +#define MALLOC_VISIBLE +#include /* * Provide definitions of memzero and memmove as some of the decompressors will -- cgit v1.2.3