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Subject[tip: x86/seves] x86/head/64: Switch to initial stack earlier
The following commit has been merged into the x86/seves branch of tip:

Commit-ID: 3add38cb96a1ae7d152db69ab4329e809c2af2d4
Gitweb: https://git.kernel.org/tip/3add38cb96a1ae7d152db69ab4329e809c2af2d4
Author: Joerg Roedel <jroedel@suse.de>
AuthorDate: Mon, 07 Sep 2020 15:15:33 +02:00
Committer: Borislav Petkov <bp@suse.de>
CommitterDate: Mon, 07 Sep 2020 21:44:01 +02:00

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
---
arch/x86/kernel/head_64.S | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index f402087..83050c9 100644
--- 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
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