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SubjectRe: [PATCH 2/5] x86-64: Allow alternative patching in the vDSO
On Tue, Jun 07, 2011 at 03:32:39PM -0400, Andy Lutomirski wrote:
> 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 | 32 ++++++++++++++++++++++++++++++++
> 1 files changed, 32 insertions(+), 0 deletions(-)
>
> diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
> index 7abd2be..b8b074c1 100644
> --- a/arch/x86/vdso/vma.c
> +++ b/arch/x86/vdso/vma.c
> @@ -23,11 +23,43 @@ 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;
> + break;
> + }
> + }
> +
> + if (!alt_sec)
> + return; /* nothing to patch */

Just a minor nitpick:

Maybe do

for (.. ) {

if (!strcmp(...)) {
alt_sec = shdr;
goto apply;
}
}
return;

apply:

to save yourself the if (!alt_sec) test and the alt_sec = 0 aka NULL
assignment above.

> +
> + 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)
> --
> 1.7.5.2

Thanks.

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
General Managers: Alberto Bozzo, Andrew Bowd
Registration: Dornach, Gemeinde Aschheim, Landkreis Muenchen
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