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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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