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Subject[PATCH v2 3/8] x86-64: Allow alternative patching in the vDSO
Date
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>
---
arch/x86/vdso/vma.c | 30 ++++++++++++++++++++++++++++++
1 files changed, 30 insertions(+), 0 deletions(-)
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 7abd2be..ba92244 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -23,11 +23,41 @@ extern unsigned short vdso_sync_cpuid;
static struct page **vdso_pages;
static unsigned vdso_size;

+static void 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;
+ }
+ }
+ 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)
--
1.7.6


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