On 05/02/2018 04:16 AM, Jan Beulich wrote:
On 30.04.18 at 18:23, boris.ostrovsky@oracle.com wrote:
--- 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)
I can only advise against doing it this way: There's no safeguard against someone changing asm/segment.h without changing this value (in fact this applies to all of the GDT selectors populated in this file). At the very least tie this to GDT_ENTRY_BOOT_TSS / __BOOT_TSS?
@@ -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 */
Without any further code before loading the selector, this points at physical address 0. Don't you need to add in the base address of the per-CPU stack_canary?
This GDT is gone soon after we jump into generic x86 startup code.That code will load its own GDT (and then set up per-cpu segments and all that).
-boris