kexec jump: check code size in control page

Kexec/Kexec-jump require code size in control page is less than PAGE_SIZE/2. This patch add link-time checking for this.

ASSERT() of ld link script is used as the link-time checking mechanism.

Signed-off-by Huang Ying <[email protected]>

---
 arch/x86/kernel/machine_kexec_32.c     |    2 +-
 arch/x86/kernel/relocate_kernel_32.S   |   10 +++++++---
 arch/x86/kernel/vmlinux_32.lds.S       |    2 ++
 arch/x86/kernel/vmlinux_check_32.lds.S |    7 +++++++
 include/asm-x86/kexec.h                |    4 ++++
 5 files changed, 21 insertions(+), 4 deletions(-)

arch/x86/kernel/machine_kexec_32.c +1 -1

@@ -138,7 +138,7 @@ void machine_kexec(struct kimage *image)
 	}
 
 	control_page = page_address(image->control_code_page);
-	memcpy(control_page, relocate_kernel, PAGE_SIZE/2);
+	memcpy(control_page, relocate_kernel, KEXEC_CONTROL_CODE_MAX_SIZE);
 
 	relocate_kernel_ptr = control_page;
 	page_list[PA_CONTROL_PAGE] = __pa(control_page);

arch/x86/kernel/relocate_kernel_32.S +4 -1

-#define DATA(offset)		(PAGE_SIZE/2+(offset))
+#define DATA(offset)		(KEXEC_CONTROL_CODE_MAX_SIZE+(offset))
 
 /* Minimal CPU state */
 #define ESP			DATA(0x0)

@@ -376,3 +377,6 @@ swap_pages:
 	popl	%ebx
 	popl	%ebp
 	ret
+
+	.globl kexec_control_code_size
+.set kexec_control_code_size, . - relocate_kernel

include/asm-x86/kexec.h +4 -0

@@ -41,6 +41,10 @@
 # define PAGES_NR		17
 #endif
 
+#ifdef CONFIG_X86_32
+# define KEXEC_CONTROL_CODE_MAX_SIZE	2048
+#endif
+
 #ifndef __ASSEMBLY__
 
 #include <linux/string.h>

arch/x86/kernel/vmlinux_32.lds.S +2 -0

@@ -209,3 +209,5 @@ SECTIONS
 
   DWARF_DEBUG
 }
+
+#include "vmlinux_check_32.lds.S"

arch/x86/kernel/relocate_kernel_32.S line 26

Quoted 12 lines

arch/x86/kernel/relocate_kernel_32.S +3 -2

@@ -20,10 +20,11 @@
 #define PAGE_ATTR (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED | _PAGE_DIRTY)
 #define PAE_PGD_ATTR (_PAGE_PRESENT)
 
-/* control_page + PAGE_SIZE/2 ~ control_page + PAGE_SIZE * 3/4 are
- * used to save some data for jumping back
+/* control_page + KEXEC_CONTROL_CODE_MAX_SIZE
+ * ~ control_page + PAGE_SIZE * 3/4 are used to save some data for
+ * jumping back
  */

Hi Huang,

Above comment is not very clear. Can you please elaborate it. I thought that PAGE_SIZE/2 is used for control code and rest half is shared between kjump data and stack. What is PAGE_SIZE *3/4?

arch/x86/kernel/relocate_kernel_32.S line 7

Quoted 9 lines

arch/x86/kernel/relocate_kernel_32.S +8 -0

+++ b/arch/x86/kernel/vmlinux_check_32.lds.S

@@ -0,0 +1,7 @@
+/*
+ * Link time checks
+ */
+
+#include <asm/kexec.h>
+
+ASSERT(kexec_control_code_size <= KEXEC_CONTROL_CODE_MAX_SIZE,

"kexec control code size is too big")

Will it make sense to move it into vmlinux_32.lds.S itself? Creating a separate
file for a single check seems superfluous.