Messages in this thread Patch in this message | | | From | YaoJun <> | Subject | [PATCH] arm64: mm: mark tramp_pg_dir read-only | Date | Wed, 30 May 2018 12:48:06 +0800 |
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To protect against KSMA(Kernel Space Mirroring Attack), make tramp_pg_dir read-only. The principle of KSMA is to insert a carefully constructed PGD entry into the translation table. The type of this entry is block, which maps the kernel text and its access permissions bits are 01. The user process can then modify kernel text directly through this mapping. In this way, an arbitrary write can be converted to multiple arbitrary writes.
Signed-off-by: YaoJun <yaojun8558363@gmail.com> --- arch/arm64/mm/mmu.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 2dbb2c9f1ec1..ac4b22c7e435 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -551,6 +551,10 @@ static int __init map_entry_trampoline(void) __create_pgd_mapping(tramp_pg_dir, pa_start, TRAMP_VALIAS, PAGE_SIZE, prot, pgd_pgtable_alloc, 0); + update_mapping_prot(__pa_symbol(tramp_pg_dir), + (unsigned long)tramp_pg_dir, + PGD_SIZE, PAGE_KERNEL_RO); + /* Map both the text and data into the kernel page table */ __set_fixmap(FIX_ENTRY_TRAMP_TEXT, pa_start, prot); if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) { -- 2.17.0
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