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    Subject[PATCH 4.9 067/102] arm64: Take into account ID_AA64PFR0_EL1.CSV3
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Will Deacon <will.deacon@arm.com>

    commit 179a56f6f9fb upstream.

    For non-KASLR kernels where the KPTI behaviour has not been overridden
    on the command line we can use ID_AA64PFR0_EL1.CSV3 to determine whether
    or not we should unmap the kernel whilst running at EL0.

    Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    [Alex: s/read_sanitised_ftr_reg/read_system_reg/ to match v4.9 naming]
    Signed-off-by: Alex Shi <alex.shi@linaro.org> [v4.9 backport]
    [Mark: correct zero bits in ftr_id_aa64pfr0 to account for CSV3]
    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/sysreg.h | 1 +
    arch/arm64/kernel/cpufeature.c | 10 ++++++++--
    2 files changed, 9 insertions(+), 2 deletions(-)

    --- a/arch/arm64/include/asm/sysreg.h
    +++ b/arch/arm64/include/asm/sysreg.h
    @@ -117,6 +117,7 @@
    #define ID_AA64ISAR0_AES_SHIFT 4

    /* id_aa64pfr0 */
    +#define ID_AA64PFR0_CSV3_SHIFT 60
    #define ID_AA64PFR0_GIC_SHIFT 24
    #define ID_AA64PFR0_ASIMD_SHIFT 20
    #define ID_AA64PFR0_FP_SHIFT 16
    --- a/arch/arm64/kernel/cpufeature.c
    +++ b/arch/arm64/kernel/cpufeature.c
    @@ -93,7 +93,8 @@ static const struct arm64_ftr_bits ftr_i
    };

    static const struct arm64_ftr_bits ftr_id_aa64pfr0[] = {
    - ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 32, 0),
    + ARM64_FTR_BITS(FTR_NONSTRICT, FTR_LOWER_SAFE, ID_AA64PFR0_CSV3_SHIFT, 4, 0),
    + ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 32, 28, 0),
    ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, 28, 4, 0),
    ARM64_FTR_BITS(FTR_STRICT, FTR_EXACT, ID_AA64PFR0_GIC_SHIFT, 4, 0),
    S_ARM64_FTR_BITS(FTR_STRICT, FTR_LOWER_SAFE, ID_AA64PFR0_ASIMD_SHIFT, 4, ID_AA64PFR0_ASIMD_NI),
    @@ -752,6 +753,8 @@ static int __kpti_forced; /* 0: not forc
    static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
    int __unused)
    {
    + u64 pfr0 = read_system_reg(SYS_ID_AA64PFR0_EL1);
    +
    /* Forced on command line? */
    if (__kpti_forced) {
    pr_info_once("kernel page table isolation forced %s by command line option\n",
    @@ -763,7 +766,9 @@ static bool unmap_kernel_at_el0(const st
    if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
    return true;

    - return false;
    + /* Defer to CPU feature registers */
    + return !cpuid_feature_extract_unsigned_field(pfr0,
    + ID_AA64PFR0_CSV3_SHIFT);
    }

    static int __init parse_kpti(char *str)
    @@ -865,6 +870,7 @@ static const struct arm64_cpu_capabiliti
    },
    #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
    {
    + .desc = "Kernel page table isolation (KPTI)",
    .capability = ARM64_UNMAP_KERNEL_AT_EL0,
    .def_scope = SCOPE_SYSTEM,
    .matches = unmap_kernel_at_el0,

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