[PATCH] arm64: allow the module region to be randomized independently

[Ard Biesheuvel]

On 8 February 2016 at 19:13, Catalin Marinas <catalin.marinas at arm.com> wrote:
> On Mon, Feb 08, 2016 at 11:12:12AM +0100, Ard Biesheuvel wrote:
>> This adds the option to randomize the module region independently from the
>> core kernel, and enables it by default. This makes it less likely that the
>> location of core kernel data structures can be determined by an adversary,
>> but causes all function calls from modules into the core kernel to be
>> resolved via entries in the module PLTs.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>  arch/arm64/Kconfig              | 15 ++++++++
>>  arch/arm64/include/asm/module.h |  6 ++++
>>  arch/arm64/kernel/kaslr.c       | 36 +++++++++++++++-----
>>  arch/arm64/kernel/module.c      |  9 ++---
>>  4 files changed, 50 insertions(+), 16 deletions(-)
>
> With this patch I get an unhandled paging request, coming from
> kernel/module.c:2982 (the memset). The PC is wrongly attributed but it's
> in arch/arm64/lib/memset.S:
>

This was due to a thinko in kaslr_early_init(). Folding the following
hunk will fix it (or I can resend the patch if you prefer)

-------8<----------
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index f8ad30160026..d7eba99ab140 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -82,6 +82,12 @@ u64 __init kaslr_early_init(u64 dt_phys)
        int size;

        /*
+        * Set a reasonable default for module_alloc_base in case
+        * we end up running with KASLR disabled.
+        */
+       module_alloc_base = (u64)_etext - MODULES_VSIZE;
+
+       /*
         * Try to map the FDT early. If this fails, we simply bail,
         * and proceed with KASLR disabled. We will make another
         * attempt at mapping the FDT in setup_machine()
-------8<----------