x86/KASLR: Update description for decompressor worst case size

The comment that describes the analysis for the size of the decompressor
code only took gzip into account (there are currently 6 other decompressors
that could be used). The actual z_extract_offset calculation in code was
already handling the correct maximum size, but this documentation hadn't
been updated. This updates the documentation, fixes several typos, moves
the comment to header.S, updates references, and adds a note at the end
of the decompressor include list to remind us about updating the comment
in the future.

(Instead of moving the comment to mkpiggy.c, where the calculation
is currently happening, it is being moved to header.S because
the calculations in mkpiggy.c will be removed in favor of header.S
calculations in a following patch, and it seemed like overkill to move
the giant comment twice, especially when there's already reference to
z_extract_offset in header.S.)

Signed-off-by: Baoquan He <bhe@redhat.com>
[ Rewrote changelog, cleaned up comment style, moved comments around. ]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: H.J. Lu <hjl.tools@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1461185746-8017-2-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 9c29e7885ef0..7d86c5dd8e99 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -155,7 +155,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
 
 	/*
 	 * Avoid the region that is unsafe to overlap during
-	 * decompression (see calculations at top of misc.c).
+	 * decompression (see calculations in ../header.S).
 	 */
 	unsafe_len = (output_size >> 12) + 32768 + 18;
 	unsafe = (unsigned long)input + input_size - unsafe_len;