diff options
| author | Will Deacon <will.deacon@arm.com> | 2017-11-14 14:38:19 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-02-16 20:22:48 +0100 |
| commit | 7fafcbb04f94d4709a5c8b7fb2c196b5bdf4fd7b (patch) | |
| tree | 45d1902fa2d286839741a2bfb3298947ac4f191a /arch/arm64/kernel/cpufeature.c | |
| parent | 2843ade2dad2249900f508f61068d245921ce9f1 (diff) | |
arm64: entry: Add fake CPU feature for unmapping the kernel at EL0
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>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/arm64/kernel/cpufeature.c')
| -rw-r--r-- | arch/arm64/kernel/cpufeature.c | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 21e2c95d24e7..1a6ec079c541 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -796,6 +796,40 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus ID_AA64PFR0_FP_SHIFT) < 0; } +#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", @@ -882,6 +916,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .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 { /* FP/SIMD is not implemented */ .capability = ARM64_HAS_NO_FPSIMD, |