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[mark.rutland@arm.com (Mark Rutland)]

On Tue, Oct 28, 2014 at 02:13:25PM +0000, Mark Rutland wrote:
> Bcc:
> Subject: Re: [PATCHv4 7/7] arm64: add better page protections to arm64
> Reply-To:
> In-Reply-To: <1414440752-9411-8-git-send-email-lauraa@codeaurora.org>

Apologies for this, I appear to have accidentally inserted a newline and
confused my mail client. I'll resend this with that fixed.

Mark.

> 
> 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.
> 
> Mark.