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x86/boot: Provide more slack space during decompression 

The current slack space is not enough for LZ4, which has a worst case
overhead of 0.4% for data that cannot be further compressed. With
an LZ4 compressed kernel with an embedded initrd, the output is likely
to overwrite the input.

Increase the slack space to avoid that.

Signed-off-by: Jan H. Schönherr <jschoenh@amazon.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1503842124-29718-1-git-send-email-jschoenh@amazon.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Jan H. Schönherr 2017-08-27 15:55:24 +02:00 committed by Ingo Molnar
parent eaa2f87c6b
commit 5746f0555d
1 changed files with 7 additions and 1 deletions
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8
arch/x86/boot/header.S
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@ -520,8 +520,14 @@ pref_address: .quad LOAD_PHYSICAL_ADDR # preferred load addr
# the description in lib/decompressor_xxx.c for specific information.
#
# extra_bytes = (uncompressed_size >> 12) + 65536 + 128
#
# LZ4 is even worse: data that cannot be further compressed grows by 0.4%,
# or one byte per 256 bytes. OTOH, we can safely get rid of the +128 as
# the size-dependent part now grows so fast.
#
# extra_bytes = (uncompressed_size >> 8) + 65536
#define ZO_z_extra_bytes ((ZO_z_output_len >> 12) + 65536 + 128)
#define ZO_z_extra_bytes ((ZO_z_output_len >> 8) + 65536)
#if ZO_z_output_len > ZO_z_input_len
# define ZO_z_extract_offset (ZO_z_output_len + ZO_z_extra_bytes - \
ZO_z_input_len)