linux-kernel - [PATCH 4.4 28/43] x86/boot: Simplify kernel load address alignment check

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Date:   Mon, 16 Jul 2018 09:36:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Brian Gerst <brgerst@...il.com>,
        Alexander Kuleshov <kuleshovmail@...il.com>,
        Borislav Petkov <bp@...e.de>,
        Alexander Popov <alpopov@...ecurity.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "Srivatsa S. Bhat" <srivatsa@...il.mit.edu>,
        "Matt Helsley (VMware)" <matt.helsley@...il.com>,
        Alexey Makhalov <amakhalov@...are.com>,
        Bo Gan <ganb@...are.com>
Subject: [PATCH 4.4 28/43] x86/boot: Simplify kernel load address alignment check

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Alexander Kuleshov <kuleshovmail@...il.com>

commit a4733143085d6c782ac1e6c85778655b6bac1d4e upstream

We are using %rax as temporary register to check the kernel
address alignment. We don't really have to since the TEST
instruction does not clobber the destination operand.

Suggested-by: Brian Gerst <brgerst@...il.com>
Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Alexander Popov <alpopov@...ecurity.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1453531828-19291-1-git-send-email-kuleshovmail@gmail.com
Link: http://lkml.kernel.org/r/1453842730-28463-11-git-send-email-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@...il.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@...il.com>
Reviewed-by: Alexey Makhalov <amakhalov@...are.com>
Reviewed-by: Bo Gan <ganb@...are.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---

 arch/x86/kernel/head_64.S |    4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -76,9 +76,7 @@ startup_64:
 	subq	$_text - __START_KERNEL_map, %rbp
 
 	/* Is the address not 2M aligned? */
-	movq	%rbp, %rax
-	andl	$~PMD_PAGE_MASK, %eax
-	testl	%eax, %eax
+	testl	$~PMD_PAGE_MASK, %ebp
 	jnz	bad_address
 
 	/*