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Subject[tip: x86/boot] x86/boot/compressed/64: Use 32-bit (zero-extended) MOV for z_output_len
The following commit has been merged into the x86/boot branch of tip:

Commit-ID: a86255fe5258714e1f7c1bdfe95f08e4d098d450
Author: Arvind Sankar <>
AuthorDate: Tue, 11 Feb 2020 12:33:33 -05:00
Committer: Borislav Petkov <>
CommitterDate: Wed, 12 Feb 2020 11:15:31 +01:00

x86/boot/compressed/64: Use 32-bit (zero-extended) MOV for z_output_len

z_output_len is the size of the decompressed payload (i.e. vmlinux +
vmlinux.relocs) and is generated as an unsigned 32-bit quantity by

The current

movq $z_output_len, %r9

instruction generates a sign-extended move to %r9. Using

movl $z_output_len, %r9d

will instead zero-extend into %r9, which is appropriate for an unsigned
32-bit quantity. This is also what is already done for z_input_len, the
size of the compressed payload.

[ bp:

Also, z_output_len cannot be a 64-bit quantity because it participates

init_size: .long INIT_SIZE # kernel initialization size

through INIT_SIZE which is a 32-bit quantity determined by the .long
directive (vs .quad for 64-bit). Furthermore, if it really must be a
64-bit quantity, then the insn must be MOVABS which can accommodate a
64-bit immediate and which the toolchain does not generate automatically.

Signed-off-by: Arvind Sankar <>
Signed-off-by: Borislav Petkov <>
arch/x86/boot/compressed/head_64.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index d1220de..68f31c4 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -482,7 +482,7 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
leaq input_data(%rip), %rdx /* input_data */
movl $z_input_len, %ecx /* input_len */
movq %rbp, %r8 /* output target address */
- movq $z_output_len, %r9 /* decompressed length, end of relocs */
+ movl $z_output_len, %r9d /* decompressed length, end of relocs */
call extract_kernel /* returns kernel location in %rax */
popq %rsi

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