[v5,33/75] x86/head/64: Switch to initial stack earlier

Commit Message

Joerg Roedel July 24, 2020, 4:02 p.m. UTC

From: Joerg Roedel <[e-mail]>

Make sure there is a stack once the kernel runs from virual 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 <[e-mail]>
---
 arch/x86/kernel/head_64.S | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Comments

Kees Cook July 24, 2020, 5:43 p.m. UTC | #1

On Fri, Jul 24, 2020 at 06:02:54PM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <[e-mail]>
> 
> Make sure there is a stack once the kernel runs from virual 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 <[e-mail]>

Reviewed-by: Kees Cook <[e-mail]>

Patch

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 057c7bd3eeb6..a5e1939d1dc9 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -200,6 +200,12 @@  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
@@ -220,9 +226,6 @@  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