On 05/02/2018 04:16 AM, Jan Beulich wrote: >>>> On 30.04.18 at 18:23, <boris.ostrovsky@xxxxxxxxxx> 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
