x86/head/64: Switch to initial stack earlier

Make sure there is a stack once the kernel runs from virtual addresses.
At this stage any secondary CPU which boots will have lost its stack
because the kernel switched to a new page-table which does not map the
real-mode stack anymore.

This is needed for handling early #VC exceptions caused by instructions
like CPUID.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-33-joro@8bytes.org

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index f402087..83050c9 100644 (file)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -192,6 +192,12 @@ SYM_CODE_START(secondary_startup_64)
        movl    initial_gs+4(%rip),%edx
        wrmsr
 
+       /*
+        * Setup a boot time stack - Any secondary CPU will have lost its stack
+        * by now because the cr3-switch above unmaps the real-mode stack
+        */
+       movq initial_stack(%rip), %rsp
+
        /* Check if nx is implemented */
        movl    $0x80000001, %eax
        cpuid
@@ -212,9 +218,6 @@ SYM_CODE_START(secondary_startup_64)
        /* Make changes effective */
        movq    %rax, %cr0
 
-       /* Setup a boot time stack */
-       movq initial_stack(%rip), %rsp
-
        /* zero EFLAGS after setting rsp */
        pushq $0
        popfq