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SubjectRe: [PATCH 2/2] livepatch: x86: make kASLR logic more accurate
On Mon, Apr 27, 2015 at 04:28:58PM +0200, Jiri Kosina wrote:
> We give up old_addr hint from the coming patch module in cases when kernel
> load base has been randomized (as in such case, the coming module has no
> idea about the exact randomization offset).
>
> We are currently too pessimistic, and give up immediately as soon as
> CONFIG_RANDOMIZE_BASE is set; this doesn't however directly imply that the
> load base has actually been randomized. There are config options that
> disable kASLR (such as hibernation), user could have disabled kaslr on
> kernel command-line, etc.
>
> The loader propagates the information whether kernel has been randomized
> through bootparams. This allows us to have the condition more accurate.
>
> On top of that, it seems unnecessary to give up old_addr hints even if
> randomization is active. The relocation offset can be computed using
> kaslr_ofsset(), and therefore old_addr can be adjusted accordingly.
>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

> ---
> arch/x86/include/asm/livepatch.h | 1 +
> kernel/livepatch/core.c | 5 +++--
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
> index 2d29197..19c099a 100644
> --- a/arch/x86/include/asm/livepatch.h
> +++ b/arch/x86/include/asm/livepatch.h
> @@ -21,6 +21,7 @@
> #ifndef _ASM_X86_LIVEPATCH_H
> #define _ASM_X86_LIVEPATCH_H
>
> +#include <asm/setup.h>
> #include <linux/module.h>
> #include <linux/ftrace.h>
>
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index 284e269..0e7c23c 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -234,8 +234,9 @@ static int klp_find_verify_func_addr(struct klp_object *obj,
> int ret;
>
> #if defined(CONFIG_RANDOMIZE_BASE)
> - /* KASLR is enabled, disregard old_addr from user */
> - func->old_addr = 0;
> + /* If KASLR has been enabled, adjust old_addr accordingly */
> + if (kaslr_enabled() && func->old_addr)
> + func->old_addr += kaslr_offset();
> #endif
>
> if (!func->old_addr || klp_is_module(obj))
> --
> Jiri Kosina
> SUSE Labs

--
Josh


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