linux-kernel - [PATCH v2] x86/boot: Use 32-bit (zero-extended) move for z_output

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Message-Id: <20200211173333.1722739-1-nivedita@alum.mit.edu>
Date:   Tue, 11 Feb 2020 12:33:33 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Michael Matz <matz@...e.de>
Subject: [PATCH v2] x86/boot: Use 32-bit (zero-extended) move 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
mkpiggy.c.

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 we already do for z_input_len, the size of
the compressed payload.

Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
v2: Improve commit message

 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 1f1f6c8139b3..03369246a4ff 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -484,7 +484,7 @@ 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
 
-- 
2.24.1