From 2f97967503df8e45bc256a348b6f050abd2a38ed Mon Sep 17 00:00:00 2001 From: James Morse Date: Tue, 15 Jan 2019 18:49:17 +0000 Subject: [PATCH] arm64: kpti: Update arm64_kernel_use_ng_mappings() when forced on Since commit b89d82ef01b3 ("arm64: kpti: Avoid rewriting early page tables when KASLR is enabled"), a kernel built with CONFIG_RANDOMIZE_BASE can decide early whether to use non-global mappings by checking the kaslr_offset(). A kernel built without CONFIG_RANDOMIZE_BASE, instead checks the cpufeature static-key. This leaves a gap where CONFIG_RANDOMIZE_BASE was enabled, no kaslr seed was provided, but kpti was forced on using the cmdline option. When the decision is made late, kpti_install_ng_mappings() will re-write the page tables, but arm64_kernel_use_ng_mappings()'s value does not change as it only tests the cpufeature static-key if CONFIG_RANDOMIZE_BASE is disabled. This function influences PROT_DEFAULT via PTE_MAYBE_NG, and causes pgattr_change_is_safe() to catch nG->G transitions when the unchanged PROT_DEFAULT is used as part of PAGE_KERNEL_RO: [ 1.942255] alternatives: patching kernel code [ 1.998288] ------------[ cut here ]------------ [ 2.000693] kernel BUG at arch/arm64/mm/mmu.c:165! [ 2.019215] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP [ 2.020257] Modules linked in: [ 2.020807] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc2 #51 [ 2.021917] Hardware name: linux,dummy-virt (DT) [ 2.022790] pstate: 40000005 (nZcv daif -PAN -UAO) [ 2.023742] pc : __create_pgd_mapping+0x508/0x6d0 [ 2.024671] lr : __create_pgd_mapping+0x500/0x6d0 [ 2.058059] Process swapper/0 (pid: 1, stack limit = 0x(____ptrval____)) [ 2.059369] Call trace: [ 2.059845] __create_pgd_mapping+0x508/0x6d0 [ 2.060684] update_mapping_prot+0x48/0xd0 [ 2.061477] mark_linear_text_alias_ro+0xdc/0xe4 [ 2.070502] smp_cpus_done+0x90/0x98 [ 2.071216] smp_init+0x100/0x114 [ 2.071878] kernel_init_freeable+0xd4/0x220 [ 2.072750] kernel_init+0x10/0x100 [ 2.073455] ret_from_fork+0x10/0x18 [ 2.075414] ---[ end trace 3572f3a7782292de ]--- [ 2.076389] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b If arm64_kernel_unmapped_at_el0() is true, arm64_kernel_use_ng_mappings() should also be true. Signed-off-by: James Morse CC: Ard Biesheuvel CC: John Garry CC: Will Deacon Signed-off-by: Will Deacon --- arch/arm64/include/asm/mmu.h | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h index ac352accb3d9..3e8063f4f9d3 100644 --- a/arch/arm64/include/asm/mmu.h +++ b/arch/arm64/include/asm/mmu.h @@ -60,8 +60,11 @@ static inline bool arm64_kernel_use_ng_mappings(void) * later determine that kpti is required, then * kpti_install_ng_mappings() will make them non-global. */ + if (arm64_kernel_unmapped_at_el0()) + return true; + if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE)) - return arm64_kernel_unmapped_at_el0(); + return false; /* * KASLR is enabled so we're going to be enabling kpti on non-broken -- 2.30.2