linux-kernel - [RFC PATCH 1/2] x86/kexec: Use linker script for relocate

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Message-ID: <20241108052241.3972433-1-dwmw2@infradead.org>
Date: Fri,  8 Nov 2024 05:22:40 +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>
Subject: [RFC PATCH 1/2] x86/kexec: Use linker script for relocate_kernel page layout

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

---
 arch/x86/include/asm/sections.h      |  1 +
 arch/x86/kernel/machine_kexec_64.c   |  6 ++++--
 arch/x86/kernel/relocate_kernel_64.S |  6 +-----
 arch/x86/kernel/vmlinux.lds.S        | 12 +++++++++++-
 4 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h
index 3fa87e5e11ab..30e8ee7006f9 100644
--- a/arch/x86/include/asm/sections.h
+++ b/arch/x86/include/asm/sections.h
@@ -5,6 +5,7 @@
 #include <asm-generic/sections.h>
 #include <asm/extable.h>
 
+extern char __relocate_kernel_start[], __relocate_kernel_end[];
 extern char __brk_base[], __brk_limit[];
 extern char __end_rodata_aligned[];
 
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 9c9ac606893e..f873bef6eefd 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -156,7 +156,7 @@ static int init_transition_pgtable(struct kimage *image, pgd_t *pgd)
 	pmd_t *pmd;
 	pte_t *pte;
 
-	vaddr = (unsigned long)relocate_kernel;
+	vaddr = (unsigned long)__relocate_kernel_start;
 	paddr = __pa(page_address(image->control_code_page)+PAGE_SIZE);
 	pgd += pgd_index(vaddr);
 	if (!pgd_present(*pgd)) {
@@ -321,6 +321,8 @@ void machine_kexec_cleanup(struct kimage *image)
  */
 void machine_kexec(struct kimage *image)
 {
+	unsigned long reloc_start = (unsigned long)__relocate_kernel_start;
+	unsigned long reloc_end = (unsigned long)__relocate_kernel_end;
 	unsigned long page_list[PAGES_NR];
 	unsigned int host_mem_enc_active;
 	int save_ftrace_enabled;
@@ -358,7 +360,7 @@ void machine_kexec(struct kimage *image)
 	}
 
 	control_page = page_address(image->control_code_page) + PAGE_SIZE;
-	__memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
+	__memcpy(control_page, __relocate_kernel_start, reloc_end - reloc_start);
 
 	page_list[PA_CONTROL_PAGE] = virt_to_phys(control_page);
 	page_list[VA_CONTROL_PAGE] = (unsigned long)control_page;
diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
index 2848d086ceb0..1efcbd340528 100644
--- a/arch/x86/kernel/relocate_kernel_64.S
+++ b/arch/x86/kernel/relocate_kernel_64.S
@@ -40,10 +40,8 @@
 #define CP_PA_SWAP_PAGE		DATA(0x28)
 #define CP_PA_BACKUP_PAGES_MAP	DATA(0x30)
 
-	.text
-	.align PAGE_SIZE
+	.section .text.relocate_kernel,"ax";
 	.code64
-SYM_CODE_START_NOALIGN(relocate_range)
 SYM_CODE_START_NOALIGN(relocate_kernel)
 	UNWIND_HINT_END_OF_STACK
 	ANNOTATE_NOENDBR
@@ -332,5 +330,3 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages)
 	int3
 SYM_CODE_END(swap_pages)
 
-	.skip KEXEC_CONTROL_CODE_MAX_SIZE - (. - relocate_kernel), 0xcc
-SYM_CODE_END(relocate_range);
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index b8c5741d2fb4..ad451371e179 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -95,7 +95,16 @@ const_pcpu_hot = pcpu_hot;
 #define BSS_DECRYPTED
 
 #endif
-
+#if defined(CONFIG_X86_64) && defined(CONFIG_KEXEC_CORE)
+#define KEXEC_RELOCATE_KERNEL_TEXT				\
+	. = ALIGN(PAGE_SIZE);					\
+	__relocate_kernel_start = .;				\
+	*(.text.relocate_kernel);				\
+	*(.rodata.relocate_kernel);				\
+	__relocate_kernel_end = .;
+#else
+#define KEXEC_RELOCATE_KERNEL_TEXT
+#endif
 PHDRS {
 	text PT_LOAD FLAGS(5);          /* R_E */
 	data PT_LOAD FLAGS(6);          /* RW_ */
@@ -124,6 +133,7 @@ SECTIONS
 		/* bootstrapping code */
 		HEAD_TEXT
 		TEXT_TEXT
+		KEXEC_RELOCATE_KERNEL_TEXT
 		SCHED_TEXT
 		LOCK_TEXT
 		KPROBES_TEXT
-- 
2.44.0