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    Subject[PATCH V34 24/29] Lock down perf when in confidentiality mode
    From
    From: David Howells <dhowells@redhat.com>

    Disallow the use of certain perf facilities that might allow userspace to
    access kernel data.

    Signed-off-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Matthew Garrett <mjg59@google.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
    ---
    include/linux/security.h | 1 +
    kernel/events/core.c | 7 +++++++
    security/lockdown/lockdown.c | 1 +
    3 files changed, 9 insertions(+)

    diff --git a/include/linux/security.h b/include/linux/security.h
    index de0d37b1fe79..53ea85889a48 100644
    --- a/include/linux/security.h
    +++ b/include/linux/security.h
    @@ -98,6 +98,7 @@ enum lockdown_reason {
    LOCKDOWN_KCORE,
    LOCKDOWN_KPROBES,
    LOCKDOWN_BPF_READ,
    + LOCKDOWN_PERF,
    LOCKDOWN_CONFIDENTIALITY_MAX,
    };

    diff --git a/kernel/events/core.c b/kernel/events/core.c
    index 72d06e302e99..77f36551756e 100644
    --- a/kernel/events/core.c
    +++ b/kernel/events/core.c
    @@ -10731,6 +10731,13 @@ SYSCALL_DEFINE5(perf_event_open,
    return -EINVAL;
    }

    + err = security_locked_down(LOCKDOWN_PERF);
    + if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
    + /* REGS_INTR can leak data, lockdown must prevent this */
    + return err;
    + else
    + err = 0;
    +
    /* Only privileged users can get physical addresses */
    if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
    diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
    index 2eea2cc13117..a7e75c614416 100644
    --- a/security/lockdown/lockdown.c
    +++ b/security/lockdown/lockdown.c
    @@ -34,6 +34,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
    [LOCKDOWN_KCORE] = "/proc/kcore access",
    [LOCKDOWN_KPROBES] = "use of kprobes",
    [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
    + [LOCKDOWN_PERF] = "unsafe use of perf",
    [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
    };

    --
    2.22.0.410.gd8fdbe21b5-goog
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