linux-kernel - [PATCH 1/7] x86/xen: Simplify set_aliased

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Message-Id: <0706f1a2538e481194514197298cca6b5e3f2638.1464129798.git.luto@kernel.org>
Date:	Tue, 24 May 2016 15:48:38 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	Andy Lutomirski <luto@...nel.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <dvrabel@...tab.net>,
	Jan Beulich <jbeulich@...e.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel <xen-devel@...ts.xen.org>
Subject: [PATCH 1/7] x86/xen: Simplify set_aliased_prot

In aa1acff356bb ("x86/xen: Probe target addresses in
set_aliased_prot() before the hypercall"), I added an explicit probe
to work around a hypercall issue.  The code can be simplified by
using probe_kernel_read.

Cc: Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: David Vrabel <dvrabel@...tab.net>
Cc: Jan Beulich <jbeulich@...e.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: xen-devel <xen-devel@...ts.xen.org>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/xen/enlighten.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 6ab672233ac9..eed696c229ba 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -521,9 +521,7 @@ static void set_aliased_prot(void *v, pgprot_t prot)
 
 	preempt_disable();
 
-	pagefault_disable();	/* Avoid warnings due to being atomic. */
-	__get_user(dummy, (unsigned char __user __force *)v);
-	pagefault_enable();
+	probe_kernel_read(&dummy, (unsigned char *)v, 1);
 
 	if (HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
 		BUG();
-- 
2.5.5