x86-64: Allow alternative patching in the vDSO

This code is short enough and different enough from the module
loader that it's not worth trying to share anything.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Link: http://lkml.kernel.org/r/e73112e4381fff29e31b882c2d0856822edaea53.1310563276.git.luto@mit.edu
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 7abd2be0f9b9..c39938d1332f 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -23,11 +23,44 @@ extern unsigned short vdso_sync_cpuid;
 static struct page **vdso_pages;
 static unsigned vdso_size;
 
+static void __init patch_vdso(void *vdso, size_t len)
+{
+        Elf64_Ehdr *hdr = vdso;
+        Elf64_Shdr *sechdrs, *alt_sec = 0;
+        char *secstrings;
+        void *alt_data;
+        int i;
+
+        BUG_ON(len < sizeof(Elf64_Ehdr));
+        BUG_ON(memcmp(hdr->e_ident, ELFMAG, SELFMAG) != 0);
+
+        sechdrs = (void *)hdr + hdr->e_shoff;
+        secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
+
+        for (i = 1; i < hdr->e_shnum; i++) {
+                Elf64_Shdr *shdr = &sechdrs[i];
+                if (!strcmp(secstrings + shdr->sh_name, ".altinstructions")) {
+                        alt_sec = shdr;
+                        goto found;
+                }
+        }
+
+        /* If we get here, it's probably a bug. */
+        pr_warning("patch_vdso: .altinstructions not found\n");
+        return;  /* nothing to patch */
+
+found:
+        alt_data = (void *)hdr + alt_sec->sh_offset;
+        apply_alternatives(alt_data, alt_data + alt_sec->sh_size);
+}
+
 static int __init init_vdso_vars(void)
 {
         int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
         int i;
 
+        patch_vdso(vdso_start, vdso_end - vdso_start);
+
         vdso_size = npages << PAGE_SHIFT;
         vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
         if (!vdso_pages)