On Wed, Apr 24, 2024 at 1:53 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote: > > Hi Brian, > > Thanks for taking a look. > > On Wed, 24 Apr 2024 at 19:39, Brian Gerst <brgerst@xxxxxxxxx> wrote: > > > > On Wed, Apr 24, 2024 at 12:06 PM Ard Biesheuvel <ardb+git@xxxxxxxxxx> wrote: > > > > > > From: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > > > > The purgatory is almost entirely position independent, without any need > > > for any relocation processing at load time except for the reference to > > > the GDT in the entry code. Generate this reference at runtime instead, > > > to remove the last R_X86_64_64 relocation from this code. > > > > > > While the GDT itself needs to be preserved in memory as long as it is > > > live, the GDT descriptor that is used to program the GDT can be > > > discarded so it can be allocated on the stack. > > > > > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > > --- > > > arch/x86/purgatory/entry64.S | 10 +++++++--- > > > 1 file changed, 7 insertions(+), 3 deletions(-) > > > > > > diff --git a/arch/x86/purgatory/entry64.S b/arch/x86/purgatory/entry64.S > > > index 9913877b0dbe..888661d9db9c 100644 > > > --- a/arch/x86/purgatory/entry64.S > > > +++ b/arch/x86/purgatory/entry64.S > > > @@ -16,7 +16,11 @@ > > > > > > SYM_CODE_START(entry64) > > > /* Setup a gdt that should be preserved */ > > > - lgdt gdt(%rip) > > > + leaq gdt(%rip), %rax > > > + pushq %rax > > > + pushw $gdt_end - gdt - 1 > > > + lgdt (%rsp) > > > + addq $10, %rsp > > > > This misaligns the stack, pushing 16 bytes on the stack but only > > removing 10 (decimal). > > > > pushw subtracts 2 from RSP and stores a word. So the total size stored > is 10 decimal not 16. I didn't notice the pushw, since I didn't think a 16-bit push was even possible in 64-bit mode. Unexpected, but clever. Brian Gerst _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
