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authorJan H. Schönherr <jschoenh@amazon.de>2017-08-27 15:55:24 +0200
committerIngo Molnar <mingo@kernel.org>2017-08-29 13:32:50 +0200
commit5746f0555d00e1cbb7bc20a2fd09041ace6f350c (patch)
treeda5c0cba57ebae270083bba262f0c77eaffbf30c /arch/x86/boot/header.S
parenteaa2f87c6b840b83827c40db6eb8481689570259 (diff)
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>
Diffstat (limited to 'arch/x86/boot/header.S')
-rw-r--r--arch/x86/boot/header.S8
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 2ed8f0c25def..1bb08ecffd24 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -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)