4.9-stable review patch. If anyone has any objections, please let me know.
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From: Will Deacon will.deacon@arm.com
commit ea1e3de85e94 upstream.
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 mark.rutland@arm.com Tested-by: Laura Abbott labbott@redhat.com Tested-by: Shanker Donthineni shankerd@codeaurora.org Signed-off-by: Will Deacon will.deacon@arm.com [Alex: use first free cpucap number, use cpus_have_cap] Signed-off-by: Alex Shi alex.shi@linaro.org [v4.9 backport] Signed-off-by: Mark Rutland mark.rutland@arm.com [v4.9 backport] Tested-by: Will Deacon will.deacon@arm.com Tested-by: Greg Hackmann ghackmann@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/include/asm/cpucaps.h | 3 +- arch/arm64/include/asm/mmu.h | 3 +- arch/arm64/kernel/cpufeature.c | 41 +++++++++++++++++++++++++++++++++++++++ arch/arm64/kernel/entry.S | 9 ++++---- 4 files changed, 50 insertions(+), 6 deletions(-)
--- a/arch/arm64/include/asm/cpucaps.h +++ b/arch/arm64/include/asm/cpucaps.h @@ -34,7 +34,8 @@ #define ARM64_HAS_32BIT_EL0 13 #define ARM64_HYP_OFFSET_LOW 14 #define ARM64_MISMATCHED_CACHE_LINE_SIZE 15 +#define ARM64_UNMAP_KERNEL_AT_EL0 16
-#define ARM64_NCAPS 16 +#define ARM64_NCAPS 17
#endif /* __ASM_CPUCAPS_H */ --- 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); --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -746,6 +746,40 @@ static bool hyp_offset_low(const struct return idmap_addr > GENMASK(VA_BITS - 2, 0) && !is_kernel_in_hyp_mode(); }
+#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, + int __unused) +{ + /* 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", @@ -829,6 +863,13 @@ static const struct arm64_cpu_capabiliti .def_scope = SCOPE_SYSTEM, .matches = hyp_offset_low, }, +#ifdef CONFIG_UNMAP_KERNEL_AT_EL0 + { + .capability = ARM64_UNMAP_KERNEL_AT_EL0, + .def_scope = SCOPE_SYSTEM, + .matches = unmap_kernel_at_el0, + }, +#endif {}, };
--- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -73,6 +73,7 @@ .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 @@ -81,6 +82,7 @@ mov x30, xzr .endif .endif +alternative_else_nop_endif #endif
sub sp, sp, #S_FRAME_SIZE @@ -208,10 +210,9 @@ 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 @@ -219,10 +220,10 @@ alternative_else_nop_endif 4: tramp_alias x30, tramp_exit_compat br x30 +#endif .else eret .endif -#endif .endm
.macro get_thread_info, rd