[Xen-devel] [PATCH v2 06/27] x86/entry/64: Adapt assembly for PIE support

[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 extended the
KASLR randomization range below the -2G memory limit.

Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
---
 arch/x86/entry/entry_64.S            | 16 ++++++++++------
 arch/x86/kernel/relocate_kernel_64.S |  8 +++-----
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index bd53c57617e6..c53123468364 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -191,7 +191,7 @@ ENTRY(entry_SYSCALL_64_trampoline)
         * spill RDI and restore it in a second-stage trampoline.
         */
        pushq   %rdi
-       movq    $entry_SYSCALL_64_stage2, %rdi
+       movabsq $entry_SYSCALL_64_stage2, %rdi
        JMP_NOSPEC %rdi
 END(entry_SYSCALL_64_trampoline)
 
@@ -1275,7 +1275,8 @@ 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
 
        /*
@@ -1480,10 +1481,10 @@ 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:
@@ -1537,7 +1538,8 @@ 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
@@ -1576,7 +1578,9 @@ first_nmi:
        addq    $8, (%rsp)      /* Fix up RSP */
        pushfq                  /* RFLAGS */
        pushq   $__KERNEL_CS    /* CS */
-       pushq   $1f             /* RIP */
+       pushq   %rax            /* Support Position Independent Code */
+       leaq    1f(%rip), %rax  /* RIP */
+       xchgq   %rax, (%rsp)    /* Restore RAX, put 1f */
        iretq                   /* continues at repeat_nmi below */
        UNWIND_HINT_IRET_REGS
 1:
diff --git a/arch/x86/kernel/relocate_kernel_64.S 
b/arch/x86/kernel/relocate_kernel_64.S
index a7227dfe1a2b..0c0fc259a4e2 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -208,11 +208,9 @@ identity_mapped:
        movq    %rax, %cr3
        lea     PAGE_SIZE(%r8), %rsp
        call    swap_pages
-       jmp     *virtual_mapped_addr(%rip)
-
-       /* Absolute value for PIE support */
-virtual_mapped_addr:
-       .quad virtual_mapped
+       movabsq $virtual_mapped, %rax
+       pushq   %rax
+       ret
 
 virtual_mapped:
        movq    RSP(%r8), %rsp
-- 
2.16.2.660.g709887971b-goog


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