[PATCH v2] x86, kaslr: Kernel base can be randomized at 0-1G offset.

[WANG Chao]

With kASLR enabled (CONFIG_RANDOMIZED_BASE=y), kernel virtual address
base is PAGE_OFFSET plus a randomized offset from 0 to 1G.

Current kexec-tools gets kernel vaddr and size from /proc/kcore. It
assumes kernel vaddr start/end is within the range [0,512M). If kaslr
enabled, kernel vaddr start/end will stay at [0+offset, 512M+offset).

To adapt kaslr, introduce a new macro X86_64_RANDOMIZED_BASE_MAX_OFFSET
to address the max offset and use this macro to filter out the kernel
text PT_LOAD from /proc/kcore.

Signed-off-by: WANG Chao <chaowang at redhat.com>
---
 kexec/arch/i386/crashdump-x86.c | 3 ++-
 kexec/arch/i386/crashdump-x86.h | 3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/kexec/arch/i386/crashdump-x86.c b/kexec/arch/i386/crashdump-x86.c
index cb19e7d..1e6d3a3 100644
--- a/kexec/arch/i386/crashdump-x86.c
+++ b/kexec/arch/i386/crashdump-x86.c
@@ -156,7 +156,8 @@ static int get_kernel_vaddr_and_size(struct kexec_info *UNUSED(info),
 
 			/* Look for kernel text mapping header. */
 			if ((saddr >= X86_64__START_KERNEL_map) &&
-			    (eaddr <= X86_64__START_KERNEL_map + X86_64_KERNEL_TEXT_SIZE)) {
+			    (saddr <= X86_64__START_KERNEL_map + X86_64_RANDOMIZE_BASE_MAX_OFFSET) &&
+			    (eaddr - saddr  < X86_64_KERNEL_TEXT_SIZE)) {
 				saddr = _ALIGN_DOWN(saddr, X86_64_KERN_VADDR_ALIGN);
 				elf_info->kern_vaddr_start = saddr;
 				size = eaddr - saddr;
diff --git a/kexec/arch/i386/crashdump-x86.h b/kexec/arch/i386/crashdump-x86.h
index e68b626..71a09f8 100644
--- a/kexec/arch/i386/crashdump-x86.h
+++ b/kexec/arch/i386/crashdump-x86.h
@@ -15,6 +15,9 @@ int load_crashdump_segments(struct kexec_info *info, char *mod_cmdline,
 #define X86_64_PAGE_OFFSET_PRE_2_6_27	0xffff810000000000ULL
 #define X86_64_PAGE_OFFSET		0xffff880000000000ULL
 
+/* kASLR - Kernel base offset could be randomized up to 1G */
+#define X86_64_RANDOMIZE_BASE_MAX_OFFSET	0x40000000
+
 #define X86_64_MAXMEM        		0x3fffffffffffUL
 
 /* Kernel text size */
-- 
1.8.5.3