diff options
| author | Will Deacon <will.deacon@arm.com> | 2017-11-14 14:38:19 +0000 |
|---|---|---|
| committer | Amit Pundir <amit.pundir@linaro.org> | 2018-01-22 13:16:20 +0530 |
| commit | c198a5539d451bfd8f5d0dd67a16b86794b09f2f (patch) | |
| tree | 3993145652ac02fb932b8fef7b2f093cfceb1474 /arch/arm64/kernel | |
| parent | 30e5ac85850a40884d376335a3daf89ae0113c5d (diff) | |
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 <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>
(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 <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Diffstat (limited to 'arch/arm64/kernel')
| -rw-r--r-- | arch/arm64/kernel/cpufeature.c | 39 | ||||
| -rw-r--r-- | arch/arm64/kernel/entry.S | 9 |
2 files changed, 44 insertions, 4 deletions
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index d2cfc1238462..9bc9847072b6 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -656,6 +656,39 @@ static bool runs_at_el2(const struct arm64_cpu_capabilities *entry) return 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) +{ + /* 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", @@ -713,6 +746,12 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .capability = ARM64_HAS_VIRT_HOST_EXTN, .matches = runs_at_el2, }, +#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 2776fc938cfa..bd6de04d866d 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 @@ -284,10 +286,9 @@ 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 @@ -295,10 +296,10 @@ alternative_else_nop_endif 4: tramp_alias x30, tramp_exit_compat br x30 +#endif .else eret .endif -#endif .endm .macro irq_stack_entry |