Re: [PATCH v7 05/12] x86/entry/64: Adapt assembly for PIE support
From: Kees Cook
Date: Mon Jun 10 2019 - 17:39:07 EST
On Mon, May 20, 2019 at 04:19:30PM -0700, Thomas Garnier wrote:
> From: Thomas Garnier <thgarnie@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> ---
> 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 20e45d9b4e15..e99b3438aa9b 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1268,7 +1268,8 @@ 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
>
> /*
> @@ -1465,10 +1466,10 @@ 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:
> @@ -1522,7 +1523,8 @@ 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
> @@ -1561,7 +1563,11 @@ first_nmi:
> addq $8, (%rsp) /* Fix up RSP */
> pushfq /* RFLAGS */
> pushq $__KERNEL_CS /* CS */
> - pushq $1f /* RIP */
> + pushq $0 /* Futur return address */
typo: Future
> + pushq %rax /* Save RAX */
> + leaq 1f(%rip), %rax /* RIP */
> + movq %rax, 8(%rsp) /* Put 1f on return address */
> + popq %rax /* Restore RAX */
> iretq /* continues at repeat_nmi below */
> UNWIND_HINT_IRET_REGS
> 1:
Other than that:
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
--
Kees Cook