From 472e95061e6a9cf05b0b908762f14be548bb1392 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 14 Nov 2017 14:38:19 +0000 Subject: [PATCH] FROMLIST: arm64: entry: Add fake CPU feature for unmapping the kernel at EL0 Allow explicit disabling of the entry trampoline on the kernel command line (kpti=off) by adding a fake CPU feature (ARM64_UNMAP_KERNEL_AT_EL0) that can be used to toggle the alternative sequences in our entry code and avoid use of the trampoline altogether if desired. This also allows us to make use of a static key in arm64_kernel_unmapped_at_el0(). Reviewed-by: Mark Rutland Tested-by: Laura Abbott Tested-by: Shanker Donthineni Signed-off-by: Will Deacon (cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git commit ea1e3de85e94d711f63437c04624aa0e8de5c8b3) Change-Id: I11cb874d12a7d0921f452c62b0752e0028a8e0a7 [ghackmann@google.com: - adjust context - apply cpucaps.h changes to cpufeature.h - replace cpus_have_const_cap() with cpus_have_cap() - tweak unmap_kernel_at_el0() declaration to match 4.4 APIs] Signed-off-by: Greg Hackmann Signed-off-by: Greg Kroah-Hartman --- arch/arm64/include/asm/cpufeature.h | 3 ++- arch/arm64/include/asm/mmu.h | 3 ++- arch/arm64/kernel/cpufeature.c | 39 +++++++++++++++++++++++++++++++++++++ arch/arm64/kernel/entry.S | 9 +++++---- 4 files changed, 48 insertions(+), 6 deletions(-) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 4c56ecdf2dc8..2c6497a042b1 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -35,8 +35,9 @@ #define ARM64_ALT_PAN_NOT_UAO 10 #define ARM64_HAS_VIRT_HOST_EXTN 11 #define ARM64_WORKAROUND_CAVIUM_27456 12 +#define ARM64_UNMAP_KERNEL_AT_EL0 23 -#define ARM64_NCAPS 13 +#define ARM64_NCAPS 24 #ifndef __ASSEMBLY__ diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h index 8e60392c9137..bb907189aef0 100644 --- a/arch/arm64/include/asm/mmu.h +++ b/arch/arm64/include/asm/mmu.h @@ -34,7 +34,8 @@ typedef struct { static inline bool arm64_kernel_unmapped_at_el0(void) { - return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0); + return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) && + cpus_have_cap(ARM64_UNMAP_KERNEL_AT_EL0); } extern void paging_init(void); diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 56cbcfba0c02..0e34add11c7a 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -650,6 +650,39 @@ static bool has_no_hw_prefetch(const struct arm64_cpu_capabilities *entry) return MIDR_IS_CPU_MODEL_RANGE(midr, MIDR_THUNDERX, rv_min, rv_max); } +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 +static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */ + +static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry) +{ + /* Forced on command line? */ + if (__kpti_forced) { + pr_info_once("kernel page table isolation forced %s by command line option\n", + __kpti_forced > 0 ? "ON" : "OFF"); + return __kpti_forced > 0; + } + + /* Useful for KASLR robustness */ + if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) + return true; + + return false; +} + +static int __init parse_kpti(char *str) +{ + bool enabled; + int ret = strtobool(str, &enabled); + + if (ret) + return ret; + + __kpti_forced = enabled ? 1 : -1; + return 0; +} +__setup("kpti=", parse_kpti); +#endif /* CONFIG_UNMAP_KERNEL_AT_EL0 */ + static const struct arm64_cpu_capabilities arm64_features[] = { { .desc = "GIC system register CPU interface", @@ -702,6 +735,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .matches = cpufeature_pan_not_uao, }, #endif /* CONFIG_ARM64_PAN */ +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 + { + .capability = ARM64_UNMAP_KERNEL_AT_EL0, + .matches = unmap_kernel_at_el0, + }, +#endif {}, }; diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 5be224cd01e7..60d69614e174 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -74,6 +74,7 @@ .macro kernel_ventry, el, label, regsize = 64 .align 7 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0 +alternative_if ARM64_UNMAP_KERNEL_AT_EL0 .if \el == 0 .if \regsize == 64 mrs x30, tpidrro_el0 @@ -82,6 +83,7 @@ mov x30, xzr .endif .endif +alternative_else_nop_endif #endif sub sp, sp, #S_FRAME_SIZE @@ -287,10 +289,9 @@ alternative_else_nop_endif ldr lr, [sp, #S_LR] add sp, sp, #S_FRAME_SIZE // restore sp -#ifndef CONFIG_UNMAP_KERNEL_AT_EL0 - eret -#else .if \el == 0 +alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0 +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 bne 4f msr far_el1, x30 tramp_alias x30, tramp_exit_native @@ -298,10 +299,10 @@ alternative_else_nop_endif 4: tramp_alias x30, tramp_exit_compat br x30 +#endif .else eret .endif -#endif .endm .macro irq_stack_entry -- 2.11.0