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>

diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index f8c796fffa0fc1b46fff7b9081aaf9c583a056d2..7cc5d3d01483ef937e7cf846fa65b1a993733900 100644 (file)
--- 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;
@@ -153,6 +188,13 @@ static int init_pgtable(struct kimage *image, unsigned long start_pgtable)
        int result;
        level4p = (pgd_t *)__va(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);