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    Subject[PATCH AUTOSEL for 4.14 157/161] powerpc/powernv: IMC fix out of bounds memory access at shutdown
    Date
    From: Nicholas Piggin <npiggin@gmail.com>

    [ Upstream commit e7bde88cdb4f0e432398a7d29ca2a15d2c18952a ]

    The OPAL IMC driver's shutdown handler disables nest PMU counters by
    walking nodes and taking the first CPU out of their cpumask, which is
    used to index into the paca (get_hard_smp_processor_id()). This does
    not always do the right thing, and in particular for CPU-less nodes it
    returns NR_CPUS and that overruns the paca and dereferences random
    memory.

    Fix it by being more careful about checking returned CPU, and only
    using online CPUs. It's not clear this shutdown code makes sense after
    commit 885dcd709b ("powerpc/perf: Add nest IMC PMU support"), but this
    should not make things worse

    Currently the bug causes us to call OPAL with a junk CPU number. A
    separate patch in development to change the way pacas are allocated
    escalates this bug into a crash:

    Unable to handle kernel paging request for data at address 0x2a21af1eeb000076
    Faulting instruction address: 0xc0000000000a5468
    Oops: Kernel access of bad area, sig: 11 [#1]
    ...
    NIP opal_imc_counters_shutdown+0x148/0x1d0
    LR opal_imc_counters_shutdown+0x134/0x1d0
    Call Trace:
    opal_imc_counters_shutdown+0x134/0x1d0 (unreliable)
    platform_drv_shutdown+0x44/0x60
    device_shutdown+0x1f8/0x350
    kernel_restart_prepare+0x54/0x70
    kernel_restart+0x28/0xc0
    SyS_reboot+0x1d0/0x2c0
    system_call+0x58/0x6c

    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/powerpc/platforms/powernv/opal-imc.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/arch/powerpc/platforms/powernv/opal-imc.c b/arch/powerpc/platforms/powernv/opal-imc.c
    index b150f4deaccf..6914b289c86b 100644
    --- a/arch/powerpc/platforms/powernv/opal-imc.c
    +++ b/arch/powerpc/platforms/powernv/opal-imc.c
    @@ -126,9 +126,11 @@ static void disable_nest_pmu_counters(void)
    const struct cpumask *l_cpumask;

    get_online_cpus();
    - for_each_online_node(nid) {
    + for_each_node_with_cpus(nid) {
    l_cpumask = cpumask_of_node(nid);
    - cpu = cpumask_first(l_cpumask);
    + cpu = cpumask_first_and(l_cpumask, cpu_online_mask);
    + if (cpu >= nr_cpu_ids)
    + continue;
    opal_imc_counters_stop(OPAL_IMC_COUNTERS_NEST,
    get_hard_smp_processor_id(cpu));
    }
    --
    2.15.1
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