[PATCH 1/2] x86/xen/pvh: Set up percpu for stack canary in 32-bit kernel entry

[Hou Wenlong]

In a 32-bit SMP kernel, the stack canary is a percpu variable accessed
as %fs:__stack_chk_guard. However, the ABI for PVH entry does not
specify the %fs register state. It currently works because the initial
%fs register is 0x10 for QEMU, which is the same as $PVH_DS_SEL.
%However, for added safety, the percpu should be set up explicitly
%before calling xen_prepare_pvh(), which accesses the stack canary.

Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
---
 arch/x86/platform/pvh/head.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/platform/pvh/head.S b/arch/x86/platform/pvh/head.S
index c4365a05ab83..cee4dadf5344 100644
--- a/arch/x86/platform/pvh/head.S
+++ b/arch/x86/platform/pvh/head.S
@@ -121,6 +121,10 @@ SYM_CODE_START_LOCAL(pvh_start_xen)
 
 	ljmp $PVH_CS_SEL, $1f
 1:
+	/* Set percpu for stack canary. */
+	mov $PVH_DS_SEL,%eax
+	mov %eax, %fs
+
 	call xen_prepare_pvh
 	mov $_pa(pvh_bootparams), %esi
 
-- 
2.31.1