linux-kernel - [RFC PATCH v2 05/16] x86/kexec: Invoke copy of relocate

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Message-ID: <20241122224715.171751-6-dwmw2@infradead.org>
Date: Fri, 22 Nov 2024 22:38:14 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: kexec@...ts.infradead.org
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Kai Huang <kai.huang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	linux-kernel@...r.kernel.org,
	Simon Horman <horms@...nel.org>,
	Dave Young <dyoung@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	jpoimboe@...nel.org
Subject: [RFC PATCH v2 05/16] x86/kexec: Invoke copy of relocate_kernel() instead of the original

From: David Woodhouse <dwmw@...zon.co.uk>

This currently calls set_memory_x() from machine_kexec_prepare() just
like the 32-bit version does. That's actually a bit earlier than I'd
like, as it leaves the page RWX all the time the image is even *loaded*.

Subsequent commits will eliminate all the writes to the page between the
point it's marked executable in machine_kexec_prepare() the time that
relocate_kernel() is running and has switched to the identmap %cr3, so
that it can be ROX. But that can't happen until it's moved to the .data
section of the kernel, and *that* can't happen until we start executing
the copy instead of executing it in place in the kernel .text. So break
the circular dependency in those commits by letting it be RWX for now.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
 arch/x86/kernel/machine_kexec_64.c   | 28 +++++++++++++++++++++-------
 arch/x86/kernel/relocate_kernel_64.S |  5 ++++-
 2 files changed, 25 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 9c9ac606893e..3aeb225a0b36 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -156,8 +156,8 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
 	pmd_t *pmd;
 	pte_t *pte;
 
-	vaddr = (unsigned long)relocate_kernel;
-	paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
+	vaddr = (unsigned long)page_address(image->control_code_page) + PAGE_SIZE;
+	paddr = __pa(vaddr);
 	pgd += pgd_index(vaddr);
 	if (!pgd_present(*pgd)) {
 		p4d = (p4d_t *)get_zeroed_page(GFP_KERNEL);
@@ -296,6 +296,7 @@ static void load_segments(void)
 
 int machine_kexec_prepare(struct kimage *image)
 {
+	void *control_page = page_address(image->control_code_page) + PAGE_SIZE;
 	unsigned long start_pgtable;
 	int result;
 
@@ -307,11 +308,17 @@ int machine_kexec_prepare(struct kimage *image)
 	if (result)
 		return result;
 
+	set_memory_x((unsigned long)control_page, 1);
+
 	return 0;
 }
 
 void machine_kexec_cleanup(struct kimage *image)
 {
+	void *control_page = page_address(image->control_code_page) + PAGE_SIZE;
+
+	set_memory_nx((unsigned long)control_page, 1);
+
 	free_transition_pgtable(image);
 }
 
@@ -321,6 +328,11 @@ void machine_kexec_cleanup(struct kimage *image)
  */
 void machine_kexec(struct kimage *image)
 {
+	unsigned long (*relocate_kernel_ptr)(unsigned long indirection_page,
+					     unsigned long page_list,
+					     unsigned long start_address,
+					     unsigned int preserve_context,
+					     unsigned int host_mem_enc_active);
 	unsigned long page_list[PAGES_NR];
 	unsigned int host_mem_enc_active;
 	int save_ftrace_enabled;
@@ -369,6 +381,8 @@ void machine_kexec(struct kimage *image)
 		page_list[PA_SWAP_PAGE] = (page_to_pfn(image->swap_page)
 						<< PAGE_SHIFT);
 
+	relocate_kernel_ptr = control_page;
+
 	/*
 	 * The segment registers are funny things, they have both a
 	 * visible and an invisible part.  Whenever the visible part is
@@ -388,11 +402,11 @@ void machine_kexec(struct kimage *image)
 	native_gdt_invalidate();
 
 	/* now call it */
-	image->start = relocate_kernel((unsigned long)image->head,
-				       (unsigned long)page_list,
-				       image->start,
-				       image->preserve_context,
-				       host_mem_enc_active);
+	image->start = relocate_kernel_ptr((unsigned long)image->head,
+					   (unsigned long)page_list,
+					   image->start,
+					   image->preserve_context,
+					   host_mem_enc_active);
 
 #ifdef CONFIG_KEXEC_JUMP
 	if (image->preserve_context)
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 92d5dbed3097..70539b1b9545 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -39,6 +39,7 @@
 #define CP_PA_TABLE_PAGE	DATA(0x20)
 #define CP_PA_SWAP_PAGE		DATA(0x28)
 #define CP_PA_BACKUP_PAGES_MAP	DATA(0x30)
+#define CP_VA_CONTROL_PAGE	DATA(0x38)
 
 	.text
 	.align PAGE_SIZE
@@ -99,6 +100,7 @@ SYM_CODE_START_NOALIGN(relocate_kernel)
 	movq	%r9, CP_PA_TABLE_PAGE(%r11)
 	movq	%r10, CP_PA_SWAP_PAGE(%r11)
 	movq	%rdi, CP_PA_BACKUP_PAGES_MAP(%r11)
+	movq	%r11, CP_VA_CONTROL_PAGE(%r11)
 
 	/* Save the preserve_context to %r11 as swap_pages clobbers %rcx. */
 	movq	%rcx, %r11
@@ -235,7 +237,8 @@ SYM_CODE_START_LOCAL_NOALIGN(identity_mapped)
 	movq	%rax, %cr3
 	lea	PAGE_SIZE(%r8), %rsp
 	call	swap_pages
-	movq	$virtual_mapped, %rax
+	movq	CP_VA_CONTROL_PAGE(%r8), %rax
+	addq	$(virtual_mapped - relocate_kernel), %rax
 	pushq	%rax
 	ANNOTATE_UNRET_SAFE
 	ret
-- 
2.47.0