On 2024/12/13 4:11, David Woodhouse wrote:
From: David Woodhouse <d...@amazon.co.uk>
The virtual mapping of the control page may have been _PAGE_GLOBAL and
thus its PTE might not have been flushed on the %cr3 switch and it might
effectively still be read-only. Move the writes to it down into the
identity_mapped() function where the same %rip-relative addressing will
get the new mapping.
The stack is fine, as that's using the identity mapped address anyway.
Fixes: 5a82223e0743 ("x86/kexec: Mark relocate_kernel page as ROX instead of
RWX")
Reported-by: Nathan Chancellor <nat...@kernel.org>
Reported-by: "Ning, Hongyu" <hongyu.n...@linux.intel.com>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219592
Signed-off-by: David Woodhouse <d...@amazon.co.uk>
Tested-by: "Ning, Hongyu" <hongyu.n...@linux.intel.com>
---
arch/x86/kernel/relocate_kernel_64.S | 32 +++++++++++++++++-----------
1 file changed, 20 insertions(+), 12 deletions(-)
diff --git a/arch/x86/kernel/relocate_kernel_64.S
b/arch/x86/kernel/relocate_kernel_64.S
index 553d67845b84..b9c80b3091c8 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -90,22 +90,17 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
movq kexec_pa_table_page(%rip), %r9
movq %r9, %cr3
- /* Save %rsp and CRs. */
- movq %rsp, saved_rsp(%rip)
- movq %rax, saved_cr3(%rip)
- movq %cr0, %rax
- movq %rax, saved_cr0(%rip)
- /* Leave CR4 in %r13 to enable the right paging mode later. */
- movq %cr4, %r13
- movq %r13, saved_cr4(%rip)
-
- /* save indirection list for jumping back */
- movq %rdi, pa_backup_pages_map(%rip)
+ /*
+ * The control page still might not be writable because the original
+ * kernel PTE may have had the _PAGE_GLOBAL bit set. Don't write to
+ * it except through the *identmap* address.
+ */
/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
movq %rcx, %r11
/* setup a new stack at the end of the physical control page */
+ movq %rsp, %rbp
lea PAGE_SIZE(%rsi), %rsp
/* jump to identity mapped page */
@@ -118,6 +113,19 @@ SYM_CODE_END(relocate_kernel)
SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
UNWIND_HINT_END_OF_STACK
+
+ /* Save original %rsp and CRs. */
+ movq %rbp, saved_rsp(%rip)
+ movq %rax, saved_cr3(%rip)
+ movq %cr0, %rax
+ movq %rax, saved_cr0(%rip)
+ /* Leave CR4 in %r13 to enable the right paging mode later. */
+ movq %cr4, %r13
+ movq %r13, saved_cr4(%rip)
+
+ /* save indirection list for jumping back */
+ movq %rdi, pa_backup_pages_map(%rip)
+
/*
* %rdi indirection page
* %rdx start address
@@ -185,7 +193,7 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
* - Machine check exception on TDX guest, if it was enabled before.
* Clearing MCE might not be allowed in TDX guests, depending on
setup.
*
- * Use R13 that contains the original CR4 value, read in
relocate_kernel().
+ * Use R13 that contains the original CR4 value
* PAE is always set in the original CR4.
*/
andl $(X86_CR4_PAE | X86_CR4_LA57), %r13d
