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Date: Thu, 30 Mar 2017 12:38:15 -0700
From: Kees Cook <keescook@...omium.org>
To: Hoeun Ryu <hoeun.ryu@...il.com>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Andy Lutomirski <luto@...nel.org>,
PaX Team <pageexec@...email.hu>, Emese Revfy <re.emese@...il.com>,
Russell King <linux@...linux.org.uk>, "x86@...nel.org" <x86@...nel.org>,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>, Christoffer Dall <christoffer.dall@...aro.org>,
Mark Rutland <mark.rutland@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
Laura Abbott <labbott@...hat.com>, Hugh Dickins <hughd@...gle.com>,
Steve Capper <steve.capper@....com>, Ganapatrao Kulkarni <gkulkarni@...iumnetworks.com>,
James Morse <james.morse@....com>, Kefeng Wang <wangkefeng.wang@...wei.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFCv2] arm64: support HAVE_ARCH_RARE_WRITE and HAVE_ARCH_RARE_WRITE_MEMCPY
On Thu, Mar 30, 2017 at 7:39 AM, Hoeun Ryu <hoeun.ryu@...il.com> wrote:
> This patch might be a part of Kees Cook's rare_write infrastructure series
> for [1] for arm64 architecture.
>
> This implementation is based on Mark Rutland's suggestions [2], which is
> that a special userspace mm that maps only __start/end_rodata as RW permi-
> ssion is prepared during early boot time (paging_init) and __arch_rare_-
> write_begin() switches to the mm [2].
>
> rare_write_mm address space is added for the special purpose and a page
> global directory is also prepared for it. The mm remaps __start_rodata ~
> __end_rodata to rodata_rw_alias_start which starts from TASK_SIZE_64 / 4
> + kaslr_offset().
>
> It passes LKDTM's rare write test.
Great work! I think this will need some further changes, though, since
it doesn't look to me like this would pass LKDTM's tests if it was
built as a module. (This is missing from my ARM attempt too... I
haven't figured out how to set the domain on the kernel modules...)
>
> [1] : http://www.openwall.com/lists/kernel-hardening/2017/02/27/5
> [2] : https://lkml.org/lkml/2017/3/29/704
>
> Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com>
> ---
> arch/arm64/Kconfig | 2 +
> arch/arm64/include/asm/pgtable.h | 4 ++
> arch/arm64/mm/mmu.c | 101 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 107 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index f2b0b52..6e2c592 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -102,6 +102,8 @@ config ARM64
> select HAVE_SYSCALL_TRACEPOINTS
> select HAVE_KPROBES
> select HAVE_KRETPROBES
> + select HAVE_ARCH_RARE_WRITE
> + select HAVE_ARCH_RARE_WRITE_MEMCPY
> select IOMMU_DMA if IOMMU_SUPPORT
> select IRQ_DOMAIN
> select IRQ_FORCED_THREADING
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index c213fdbd0..1514933 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -741,6 +741,10 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
> #define kc_vaddr_to_offset(v) ((v) & ~VA_START)
> #define kc_offset_to_vaddr(o) ((o) | VA_START)
>
> +unsigned long __arch_rare_write_begin(void);
> +unsigned long __arch_rare_write_end(void);
> +void __arch_rare_write_memcpy(void *dst, const void *src, __kernel_size_t len);
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* __ASM_PGTABLE_H */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 91502e3..86b25c9 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -570,6 +570,105 @@ static void __init map_kernel(pgd_t *pgd)
> kasan_copy_shadow(pgd);
> }
>
> +struct mm_struct rare_write_mm = {
> + .mm_rb = RB_ROOT,
> + .mm_users = ATOMIC_INIT(2),
> + .mm_count = ATOMIC_INIT(1),
> + .mmap_sem = __RWSEM_INITIALIZER(rare_write_mm.mmap_sem),
> + .page_table_lock= __SPIN_LOCK_UNLOCKED(rare_write_mm.page_table_lock),
> + .mmlist = LIST_HEAD_INIT(rare_write_mm.mmlist),
> +};
> +
> +#ifdef CONFIG_ARM64_PTDUMP_DEBUGFS
> +#include <asm/ptdump.h>
> +
> +static struct ptdump_info rare_write_ptdump_info = {
> + .mm = &rare_write_mm,
> + .markers = (struct addr_marker[]){
> + { 0, "rare-write start" },
> + { TASK_SIZE_64, "rare-write end" }
> + },
> + .base_addr = 0,
> +};
> +
> +static int __init ptdump_init(void)
> +{
> + return ptdump_debugfs_register(&rare_write_ptdump_info,
> + "rare_write_page_tables");
> +}
> +device_initcall(ptdump_init);
> +
> +#endif
> +
> +__always_inline unsigned long __arch_rare_write_begin(void)
> +{
> + struct mm_struct *mm = &rare_write_mm;
> +
> + preempt_disable();
> +
> + __switch_mm(mm);
Can you include a BUG_ON check here that rare_write_mm is not already active?
> +
> + if (system_uses_ttbr0_pan()) {
> + update_saved_ttbr0(current, mm);
> + cpu_switch_mm(mm->pgd, mm);
> + }
> +
> + return 0;
> +}
> +
> +__always_inline unsigned long __arch_rare_write_end(void)
> +{
> + struct mm_struct *mm = current->active_mm;
> +
> + __switch_mm(mm);
And same here (though the reverse test)?
> +
> + if (system_uses_ttbr0_pan()) {
> + cpu_set_reserved_ttbr0();
> + if (mm != &init_mm)
> + update_saved_ttbr0(current, mm);
> + }
> +
> + preempt_enable_no_resched();
> +
> + return 0;
> +}
> +
> +static unsigned long rodata_rw_alias_start __ro_after_init = TASK_SIZE_64 / 4;
> +
> +__always_inline void __arch_rare_write_memcpy(void *dst, const void *src,
> + __kernel_size_t len)
> +{
> + unsigned long __dst = (unsigned long)dst;
> +
> + __dst -= (unsigned long)__start_rodata;
> + __dst += rodata_rw_alias_start;
> +
> + memcpy((void *)__dst, src, len);
> +}
> +
> +void __init rare_write_init(void)
> +{
> + phys_addr_t pgd_phys = early_pgtable_alloc();
> + pgd_t *pgd = (pgd_t *)__phys_to_virt(pgd_phys);
> + phys_addr_t pa_start = __pa_symbol(__start_rodata);
> + unsigned long size = __end_rodata - __start_rodata;
> +
> + BUG_ON(!PAGE_ALIGNED(pa_start));
> + BUG_ON(!PAGE_ALIGNED(size));
> +
> + rodata_rw_alias_start += kaslr_offset();
> +
> + BUG_ON(rodata_rw_alias_start + size > TASK_SIZE_64);
> +
> + rare_write_mm.pgd = pgd;
> + init_new_context(NULL, &rare_write_mm);
> +
> + __create_pgd_mapping(pgd,
> + pa_start, rodata_rw_alias_start, size,
> + __pgprot(pgprot_val(PAGE_KERNEL) | PTE_NG),
> + early_pgtable_alloc, debug_pagealloc_enabled());
> +}
> +
> /*
> * paging_init() sets up the page tables, initialises the zone memory
> * maps and sets up the zero page.
> @@ -603,6 +702,8 @@ void __init paging_init(void)
> */
> memblock_free(__pa_symbol(swapper_pg_dir) + PAGE_SIZE,
> SWAPPER_DIR_SIZE - PAGE_SIZE);
> +
> + rare_write_init();
> }
>
> /*
> --
> 2.7.4
>
Thanks!
-Kees
--
Kees Cook
Pixel Security
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