Comment 12 for bug 1857074

We certainly want this:

commit 71c751f2a43fa03fae3cf5f0067ed3001a397013
Author: Mark Rutland <email address hidden>
Date: Mon Apr 23 11:41:33 2018 +0100

    arm64: add sentinel to kpti_safe_list

    We're missing a sentinel entry in kpti_safe_list. Thus is_midr_in_range_list()
    can walk past the end of kpti_safe_list. Depending on the contents of memory,
    this could erroneously match a CPU's MIDR, cause a data abort, or other bad
    outcomes.

    Add the sentinel entry to avoid this.

    Fixes: be5b299830c63ed7 ("arm64: capabilities: Add support for checks based on a list of MIDRs")
    Signed-off-by: Mark Rutland <email address hidden>
    Reported-by: Jan Kiszka <email address hidden>
    Tested-by: Jan Kiszka <email address hidden>
    Reviewed-by: Suzuki K Poulose <email address hidden>
    Cc: Catalin Marinas <email address hidden>
    Cc: Suzuki K Poulose <email address hidden>
    Cc: Will Deacon <email address hidden>
    Signed-off-by: Will Deacon <email address hidden>

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 536d572e5596..9d1b06d67c53 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -868,6 +868,7 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
        static const struct midr_range kpti_safe_list[] = {
                MIDR_ALL_VERSIONS(MIDR_CAVIUM_THUNDERX2),
                MIDR_ALL_VERSIONS(MIDR_BRCM_VULCAN),
+ { /* sentinel */ }
        };
        char const *str = "command line option";