[PATCH v6 07/11] arm64/mmu: ignore debug_pagealloc for kernel segments

Ard Biesheuvel
2017-03-09T20:52:05Z

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.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
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 bb9179084217..ec23aec6433f 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