x86, kexec: x86_64: add identity map for pages at image->start

Impact: Fix corner case that cannot yet occur

image->start may be outside of 0 ~ max_pfn, for example when jumping
back to original kernel from kexeced kenrel. This patch add identity
map for pages at image->start.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index f8c796fffa0f..7cc5d3d01483 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -18,6 +18,41 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 
+static int init_one_level2_page(struct kimage *image, pgd_t *pgd,
+                                unsigned long addr)
+{
+        pud_t *pud;
+        pmd_t *pmd;
+        struct page *page;
+        int result = -ENOMEM;
+
+        addr &= PMD_MASK;
+        pgd += pgd_index(addr);
+        if (!pgd_present(*pgd)) {
+                page = kimage_alloc_control_pages(image, 0);
+                if (!page)
+                        goto out;
+                pud = (pud_t *)page_address(page);
+                memset(pud, 0, PAGE_SIZE);
+                set_pgd(pgd, __pgd(__pa(pud) | _KERNPG_TABLE));
+        }
+        pud = pud_offset(pgd, addr);
+        if (!pud_present(*pud)) {
+                page = kimage_alloc_control_pages(image, 0);
+                if (!page)
+                        goto out;
+                pmd = (pmd_t *)page_address(page);
+                memset(pmd, 0, PAGE_SIZE);
+                set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE));
+        }
+        pmd = pmd_offset(pud, addr);
+        if (!pmd_present(*pmd))
+                set_pmd(pmd, __pmd(addr | __PAGE_KERNEL_LARGE_EXEC));
+        result = 0;
+out:
+        return result;
+}
+
 static void init_level2_page(pmd_t *level2p, unsigned long addr)
 {
         unsigned long end_addr;
@@ -155,6 +190,13 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
         result = init_level4_page(image, level4p, 0, max_pfn << PAGE_SHIFT);
         if (result)
                 return result;
+        /*
+         * image->start may be outside 0 ~ max_pfn, for example when
+         * jump back to original kernel from kexeced kernel
+         */
+        result = init_one_level2_page(image, level4p, image->start);
+        if (result)
+                return result;
         return init_transition_pgtable(image, level4p);
 }