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Date: Thu, 9 Mar 2017 17:51:17 +0000
From: Mark Rutland <mark.rutland@....com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: linux-arm-kernel@...ts.infradead.org, keescook@...omium.org,
labbott@...oraproject.org, kernel-hardening@...ts.openwall.com,
will.deacon@....com, catalin.marinas@....com,
kvmarm@...ts.cs.columbia.edu, marc.zyngier@....com
Subject: Re: [PATCH v5 07/10] arm64/mmu: ignore debug_pagealloc for kernel
segments
On Thu, Mar 09, 2017 at 09:25:09AM +0100, Ard Biesheuvel wrote:
> The debug_pagealloc facility manipulates kernel mappings in the linear
> region at page granularity to detect out of bounds or use-after-free
> accesses. Since the kernel segments are not allocated dynamically,
> there is no point in taking the debug_pagealloc_enabled flag into
> account for them, and we can use block mappings unconditionally.
>
> Note that this applies equally to the linear alias of text/rodata:
> we will never have dynamic allocations there given that the same
> memory is statically in use by the kernel image.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
This makes sense to me, and I haven't found anything this breaks.
It may be worth noting that a similar reasoning already applies the the
FDT mapping, where we use create_mapping_noalloc(), and never mandate
page mappings.
Regardless:
Reviewed-by: Mark Rutland <mark.rutland@....com>
Mark.
> ---
> arch/arm64/mm/mmu.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index c3963c592ec3..d3fecd20a136 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -328,8 +328,7 @@ static void update_mapping_prot(phys_addr_t phys, unsigned long virt,
> return;
> }
>
> - __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot,
> - NULL, debug_pagealloc_enabled());
> + __create_pgd_mapping(init_mm.pgd, phys, virt, size, prot, NULL, false);
>
> /* flush the TLBs after updating live kernel mappings */
> flush_tlb_kernel_range(virt, virt + size);
> @@ -381,7 +380,7 @@ static void __init __map_memblock(pgd_t *pgd, phys_addr_t start, phys_addr_t end
> */
> __create_pgd_mapping(pgd, kernel_start, __phys_to_virt(kernel_start),
> kernel_end - kernel_start, PAGE_KERNEL,
> - early_pgtable_alloc, debug_pagealloc_enabled());
> + early_pgtable_alloc, false);
> }
>
> void __init mark_linear_text_alias_ro(void)
> @@ -437,7 +436,7 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
> BUG_ON(!PAGE_ALIGNED(size));
>
> __create_pgd_mapping(pgd, pa_start, (unsigned long)va_start, size, prot,
> - early_pgtable_alloc, debug_pagealloc_enabled());
> + early_pgtable_alloc, false);
>
> vma->addr = va_start;
> vma->phys_addr = pa_start;
> --
> 2.7.4
>
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