[PATCHv4 7/7] arm64: add better page protections to arm64

[lauraa@codeaurora.org (Laura Abbott)]

On 10/28/2014 7:20 AM, Mark Rutland wrote:
> [resending due to previous header destruction]
>
> Hi Laura,
>
> On Mon, Oct 27, 2014 at 08:12:32PM +0000, Laura Abbott wrote:
>> Add page protections for arm64 similar to those in arm.
>> This is for security reasons to prevent certain classes
>> of exploits. The current method:
>>
>> - Map all memory as either RWX or RW. We round to the nearest
>>    section to avoid creating page tables before everything is mapped
>> - Once everything is mapped, if either end of the RWX section should
>>    not be X, we split the PMD and remap as necessary
>> - When initmem is to be freed, we change the permissions back to
>>    RW (using stop machine if necessary to flush the TLB)
>> - If CONFIG_DEBUG_RODATA is set, the read only sections are set
>>    read only.
>>
>> Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
>> ---
>> v4: Combined the Kconfig options
>> ---
>>   arch/arm64/Kconfig.debug            |  23 +++
>>   arch/arm64/include/asm/cacheflush.h |   4 +
>>   arch/arm64/kernel/vmlinux.lds.S     |  17 ++
>>   arch/arm64/mm/init.c                |   1 +
>>   arch/arm64/mm/mm.h                  |   2 +
>>   arch/arm64/mm/mmu.c                 | 303 +++++++++++++++++++++++++++++++-----
>>   6 files changed, 314 insertions(+), 36 deletions(-)
>
> With this patch applied to v3.18-rc2, my board to blows up at boot when
> using UEFI (without DEBUG_RODATA selected):
>
> ---->8----
> EFI stub: Booting Linux Kernel...
> Initializing cgroup subsys cpu
> Linux version 3.18.0-rc2+ (mark at leverpostej) (gcc version 4.9.2 20140904 (prerelease) (crosstool-NG linaro-1.13.1-4.9-2014.09 - Linaro GCC 4.9-2014.09) ) #112 SMP PREEMPT Tue Oct 28 13:58:41 GMT 2014
> CPU: AArch64 Processor [410fd030] revision 0
> Detected VIPT I-cache on CPU0
> bootconsole [uart0] enabled
> efi: Getting EFI parameters from FDT:
> EFI v2.40 by ARM Juno EFI Oct  7 2014 15:05:42
> efi:  ACPI=0xfebdc000  ACPI 2.0=0xfebdc014
> cma: Reserved 16 MiB at fd800000
> BUG: failure at arch/arm64/mm/mmu.c:234/alloc_init_pmd()!
> Kernel panic - not syncing: BUG!
> CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc2+ #112
> Call trace:
> [<ffffffc000087ec8>] dump_backtrace+0x0/0x124
> [<ffffffc000087ffc>] show_stack+0x10/0x1c
> [<ffffffc0004ebd58>] dump_stack+0x74/0xb8
> [<ffffffc0004eb018>] panic+0xe0/0x220
> [<ffffffc0004e8e08>] alloc_init_pmd+0x1cc/0x1dc
> [<ffffffc0004e8e3c>] alloc_init_pud+0x24/0x6c
> [<ffffffc0004e8f54>] __create_mapping+0xd0/0xf0
> [<ffffffc00069a0a0>] create_id_mapping+0x5c/0x68
> [<ffffffc00069964c>] efi_idmap_init+0x54/0xd8
> [<ffffffc0006978a8>] setup_arch+0x408/0x5c0
> [<ffffffc00069566c>] start_kernel+0x94/0x3a0
> ---[ end Kernel panic - not syncing: BUG!
> ---->8----
>
> I've not yet figured out precisely why. I haven't tried a !EFI boot
> because of the way my board is set up at the moment.
>

I think it's because the idmap is now being created earlier than
expected so it's trying to get memory from the normal allocator
and dying. I'll have to see if I can get my hands on an EFI
board and test it out.

Thanks,
Laura

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