[RFC PATCH 21/28] x86/head: Use PIC-compatible symbol references in startup code

[Ard Biesheuvel <ardb+git@xxxxxxxxxx>]

From: Ard Biesheuvel <ardb@xxxxxxxxxx>

Use RIP-relative symbol references to make them compatible with running
the linker in PIE mode.

Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
---
 arch/x86/kernel/head_64.S            | 14 +++++++++-----
 arch/x86/kernel/relocate_kernel_64.S |  6 ++++--
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index db71cf64204b..cc2fec3de4b7 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -182,8 +182,9 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, 
SYM_L_GLOBAL)
        xorl    %r15d, %r15d
 
        /* Derive the runtime physical address of init_top_pgt[] */
-       movq    phys_base(%rip), %rax
-       addq    $(init_top_pgt - __START_KERNEL_map), %rax
+       leaq    init_top_pgt(%rip), %rax
+       subq    $__START_KERNEL_map, %rax
+       addq    phys_base(%rip), %rax
 
        /*
         * Retrieve the modifier (SME encryption mask if SME is active) to be
@@ -314,7 +315,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
 
 .Lsetup_cpu:
        /* Get the per cpu offset for the given CPU# which is in ECX */
-       movq    __per_cpu_offset(,%rcx,8), %rdx
+       leaq    __per_cpu_offset(%rip), %rdx
+       movq    (%rdx,%rcx,8), %rdx
 #else
        xorl    %edx, %edx /* zero-extended to clear all of RDX */
 #endif /* CONFIG_SMP */
@@ -325,7 +327,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
         *
         * RDX contains the per-cpu offset
         */
-       movq    pcpu_hot + X86_current_task(%rdx), %rax
+       leaq    pcpu_hot + X86_current_task(%rip), %rax
+       movq    (%rax,%rdx), %rax
        movq    TASK_threadsp(%rax), %rsp
 
        /*
@@ -346,7 +349,8 @@ SYM_INNER_LABEL(common_startup_64, SYM_L_LOCAL)
         */
        subq    $16, %rsp
        movw    $(GDT_SIZE-1), (%rsp)
-       leaq    gdt_page(%rdx), %rax
+       leaq    gdt_page(%rip), %rax
+       addq    %rdx, %rax
        movq    %rax, 2(%rsp)
        lgdt    (%rsp)
        addq    $16, %rsp
diff --git a/arch/x86/kernel/relocate_kernel_64.S 
b/arch/x86/kernel/relocate_kernel_64.S
index e9e88c342f75..cbfd0227ea3e 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -106,6 +106,9 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
        /* setup a new stack at the end of the physical control page */
        lea     PAGE_SIZE(%r8), %rsp
 
+       /* take the virtual address of virtual_mapped() before jumping */
+       leaq    virtual_mapped(%rip), %r14
+
        /* jump to identity mapped page */
        addq    $(identity_mapped - relocate_kernel), %r8
        pushq   %r8
@@ -225,8 +228,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
        movq    %rax, %cr3
        lea     PAGE_SIZE(%r8), %rsp
        call    swap_pages
-       movq    $virtual_mapped, %rax
-       pushq   %rax
+       pushq   %r14
        ANNOTATE_UNRET_SAFE
        ret
        int3
-- 
2.46.0.792.g87dc391469-goog