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Subject[PATCH v3 1/2] xen/PVH: Set up GS segment for stack canary
Date
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@oracle.com>
---
arch/x86/xen/xen-pvh.S | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/xen-pvh.S b/arch/x86/xen/xen-pvh.S
index e1a5fbe..0db540c 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
@@ -98,6 +104,12 @@ ENTRY(pvh_start_xen)
/* 64-bit entry point. */
.code64
1:
+ /* Set base address in stack canary descriptor. */
+ mov $MSR_GS_BASE,%ecx
+ mov $canary, %rax
+ cdq
+ wrmsr
+
call xen_prepare_pvh

/* startup_64 expects boot_params in %rsi. */
@@ -107,6 +119,14 @@ ENTRY(pvh_start_xen)

#else /* CONFIG_X86_64 */

+ /* Set base address in stack canary descriptor. */
+ movl _pa(gdt_start),%eax
+ movl $_pa(canary),%ecx
+ movw %cx, (PVH_GDT_ENTRY_CANARY * 8) + 0(%eax)
+ shrl $16, %ecx
+ movb %cl, (PVH_GDT_ENTRY_CANARY * 8) + 2(%eax)
+ movb %ch, (PVH_GDT_ENTRY_CANARY * 8) + 5(%eax)
+
call mk_early_pgtbl_32

mov $_pa(initial_page_table), %eax
@@ -150,9 +170,12 @@ gdt_start:
.quad GDT_ENTRY(0xc09a, 0, 0xfffff) /* __KERNEL_CS */
#endif
.quad GDT_ENTRY(0xc092, 0, 0xfffff) /* __KERNEL_DS */
+ .quad GDT_ENTRY(0x4090, 0, 0x18) /* PVH_CANARY_SEL */
gdt_end:

- .balign 4
+ .balign 16
+canary:
+ .fill 24, 1, 0
early_stack:
.fill 256, 1, 0
early_stack_end:
--
2.9.3
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