On Mon, Aug 5, 2019 at 10:28 AM Borislav Petkov <bp@xxxxxxxxx> wrote: > > On Tue, Jul 30, 2019 at 12:12:48PM -0700, Thomas Garnier wrote: > > Change the assembly code to use only relative references of symbols for the > > kernel to be PIE compatible. > > > > Position Independent Executable (PIE) support will allow to extend the > > KASLR randomization range below 0xffffffff80000000. > > > > Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxxxx> > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > arch/x86/entry/entry_64.S | 16 +++++++++++----- > > 1 file changed, 11 insertions(+), 5 deletions(-) > > > > diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > > index 3f5a978a02a7..4b588a902009 100644 > > --- a/arch/x86/entry/entry_64.S > > +++ b/arch/x86/entry/entry_64.S > > @@ -1317,7 +1317,8 @@ ENTRY(error_entry) > > movl %ecx, %eax /* zero extend */ > > cmpq %rax, RIP+8(%rsp) > > je .Lbstep_iret > > - cmpq $.Lgs_change, RIP+8(%rsp) > > + leaq .Lgs_change(%rip), %rcx > > + cmpq %rcx, RIP+8(%rsp) > > jne .Lerror_entry_done > > > > /* > > @@ -1514,10 +1515,10 @@ ENTRY(nmi) > > * resume the outer NMI. > > */ > > > > - movq $repeat_nmi, %rdx > > + leaq repeat_nmi(%rip), %rdx > > cmpq 8(%rsp), %rdx > > ja 1f > > - movq $end_repeat_nmi, %rdx > > + leaq end_repeat_nmi(%rip), %rdx > > cmpq 8(%rsp), %rdx > > ja nested_nmi_out > > 1: > > @@ -1571,7 +1572,8 @@ nested_nmi: > > pushq %rdx > > pushfq > > pushq $__KERNEL_CS > > - pushq $repeat_nmi > > + leaq repeat_nmi(%rip), %rdx > > + pushq %rdx > > > > /* Put stack back */ > > addq $(6*8), %rsp > > @@ -1610,7 +1612,11 @@ first_nmi: > > addq $8, (%rsp) /* Fix up RSP */ > > pushfq /* RFLAGS */ > > pushq $__KERNEL_CS /* CS */ > > - pushq $1f /* RIP */ > > + pushq $0 /* Future return address */ > > + pushq %rax /* Save RAX */ > > + leaq 1f(%rip), %rax /* RIP */ > > + movq %rax, 8(%rsp) /* Put 1f on return address */ > > + popq %rax /* Restore RAX */ > > Can't you just use a callee-clobbered reg here instead of preserving > %rax? I saw that %rdx was used for temporary usage and restored before the end so I assumed that it was not an option. > > -- > Regards/Gruss, > Boris. > > Good mailing practices for 400: avoid top-posting and trim the reply.
