From 2f7c68cb55ecb7331f2381deb497c27155f32faf Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Wed, 03 Jan 2024 09:43:39 +0000
Subject: [PATCH] update kernel to 5.10.198

---
 kernel/arch/x86/boot/compressed/head_64.S |   30 +++++++++++++++++++++++-------
 1 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/kernel/arch/x86/boot/compressed/head_64.S b/kernel/arch/x86/boot/compressed/head_64.S
index b55e200..473d84e 100644
--- a/kernel/arch/x86/boot/compressed/head_64.S
+++ b/kernel/arch/x86/boot/compressed/head_64.S
@@ -454,11 +454,25 @@
 	/* Save the trampoline address in RCX */
 	movq	%rax, %rcx
 
+	/* Set up 32-bit addressable stack */
+	leaq	TRAMPOLINE_32BIT_STACK_END(%rcx), %rsp
+
 	/*
-	 * Load the address of trampoline_return() into RDI.
-	 * It will be used by the trampoline to return to the main code.
+	 * Preserve live 64-bit registers on the stack: this is necessary
+	 * because the architecture does not guarantee that GPRs will retain
+	 * their full 64-bit values across a 32-bit mode switch.
+	 */
+	pushq	%rbp
+	pushq	%rbx
+	pushq	%rsi
+
+	/*
+	 * Push the 64-bit address of trampoline_return() onto the new stack.
+	 * It will be used by the trampoline to return to the main code. Due to
+	 * the 32-bit mode switch, it cannot be kept it in a register either.
 	 */
 	leaq	trampoline_return(%rip), %rdi
+	pushq	%rdi
 
 	/* Switch to compatibility mode (CS.L = 0 CS.D = 1) via far return */
 	pushq	$__KERNEL32_CS
@@ -466,6 +480,11 @@
 	pushq	%rax
 	lretq
 trampoline_return:
+	/* Restore live 64-bit registers */
+	popq	%rsi
+	popq	%rbx
+	popq	%rbp
+
 	/* Restore the stack, the 32-bit trampoline uses its own stack */
 	leaq	rva(boot_stack_end)(%rbx), %rsp
 
@@ -586,7 +605,7 @@
 /*
  * This is the 32-bit trampoline that will be copied over to low memory.
  *
- * RDI contains the return address (might be above 4G).
+ * Return address is at the top of the stack (might be above 4G).
  * ECX contains the base address of the trampoline memory.
  * Non zero RDX means trampoline needs to enable 5-level paging.
  */
@@ -595,9 +614,6 @@
 	movl	$__KERNEL_DS, %eax
 	movl	%eax, %ds
 	movl	%eax, %ss
-
-	/* Set up new stack */
-	leal	TRAMPOLINE_32BIT_STACK_END(%ecx), %esp
 
 	/* Disable paging */
 	movl	%cr0, %eax
@@ -658,7 +674,7 @@
 	.code64
 SYM_FUNC_START_LOCAL_NOALIGN(.Lpaging_enabled)
 	/* Return from the trampoline */
-	jmp	*%rdi
+	retq
 SYM_FUNC_END(.Lpaging_enabled)
 
 	/*

--
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