linux-kernel - [PATCH 3/4] xen/PVH: Set up GS segment for stack canary

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Date:   Mon, 30 Apr 2018 12:23:38 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     jgross@...e.com, Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        stable@...r.kernel.org
Subject: [PATCH 3/4] xen/PVH: Set up GS segment for stack canary

We are making calls to C code (e.g. xen_prepare_pvh()) which may use
stack canary (stored in GS segment).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: stable@...r.kernel.org
---
 arch/x86/xen/xen-pvh.S | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
index 373fef0..4eed586 100644
--- a/arch/x86/xen/xen-pvh.S
+++ b/arch/x86/xen/xen-pvh.S
@@ -54,6 +54,9 @@
  * charge of setting up it's own stack, GDT and IDT.
  */
 
+#define PVH_GDT_ENTRY_CANARY    4
+#define PVH_CANARY_SEL          (PVH_GDT_ENTRY_CANARY * 8)
+
 ENTRY(pvh_start_xen)
 	cld
 
@@ -64,6 +67,9 @@ ENTRY(pvh_start_xen)
 	mov %eax,%es
 	mov %eax,%ss
 
+	mov $(PVH_CANARY_SEL),%eax
+	mov %eax,%gs
+
 	/* Stash hvm_start_info. */
 	mov $_pa(pvh_start_info), %edi
 	mov %ebx, %esi
@@ -150,6 +156,7 @@ gdt_start:
 	.quad 0x00cf9a000000ffff            /* __BOOT_CS */
 #endif
 	.quad 0x00cf92000000ffff            /* __BOOT_DS */
+	.quad 0x0040900000000018            /* PVH_CANARY_SEL */
 gdt_end:
 
 	.balign 4
-- 
2.9.3