livepatch: x86: make kASLR logic more accurate

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.

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
index 2d29197bd2fbfb7da88b1b3f9c9c932a78e177a5..19c099afa8613ead6565917f5787deb3df12c9e7 100644 (file)
--- 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 284e2691e38073d52b00d46010e654e6ff7de9bf..0e7c23c6cf3fd555353f156a2504000f3be4ff90 100644 (file)
--- 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))