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From: Juergen Gross <jgross@suse.com>
To: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org
Cc: boris.ostrovsky@oracle.com, Juergen Gross <jgross@suse.com>,
	stable@vger.kernel.org
Subject: [PATCH] x86/xen: init %gs very early to avoid page faults with stack protector
Date: Thu,  1 Feb 2018 13:16:01 +0100	[thread overview]
Message-ID: <20180201121601.1268-1-jgross@suse.com> (raw)

When running as Xen pv guest %gs is initialized some time after
C code is started. Depending on stack protector usage this might be
too late, resulting in page faults.

So setup %gs and MSR_GS_BASE in assembly code already.

Cc: stable@vger.kernel.org
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/xen-head.S | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index 497cc55a0c16..b47d87076efb 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -9,7 +9,9 @@
 
 #include <asm/boot.h>
 #include <asm/asm.h>
+#include <asm/msr.h>
 #include <asm/page_types.h>
+#include <asm/percpu.h>
 #include <asm/unwind_hints.h>
 
 #include <xen/interface/elfnote.h>
@@ -35,6 +37,18 @@ ENTRY(startup_xen)
 	mov %_ASM_SI, xen_start_info
 	mov $init_thread_union+THREAD_SIZE, %_ASM_SP
 
+	/* Set up %gs.
+	 *
+	 * The base of %gs always points to the bottom of the irqstack
+	 * union.  If the stack protector canary is enabled, it is
+	 * located at %gs:40.  Note that, on SMP, the boot cpu uses
+	 * init data section till per cpu areas are set up.
+	 */
+	movl	$MSR_GS_BASE,%ecx
+	movq	$INIT_PER_CPU_VAR(irq_stack_union),%rax
+	cdq
+	wrmsr
+
 	jmp xen_start_kernel
 END(startup_xen)
 	__FINIT
-- 
2.13.6

             reply	other threads:[~2018-02-01 12:16 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-01 12:16 Juergen Gross [this message]
2018-02-01 12:22 ` [PATCH] x86/xen: init %gs very early to avoid page faults with stack protector Andrew Cooper
2018-02-01 12:24   ` Juergen Gross

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