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    Subject[PATCH 5.15 096/779] powerpc/powernv: Avoid crashing if rng is NULL
    Date
    From: Michael Ellerman <mpe@ellerman.id.au>

    commit 90b5d4fe0b3ba7f589c6723c6bfb559d9e83956a upstream.

    On a bare-metal Power8 system that doesn't have an "ibm,power-rng", a
    malicious QEMU and guest that ignore the absence of the
    KVM_CAP_PPC_HWRNG flag, and calls H_RANDOM anyway, will dereference a
    NULL pointer.

    In practice all Power8 machines have an "ibm,power-rng", but let's not
    rely on that, add a NULL check and early return in
    powernv_get_random_real_mode().

    Fixes: e928e9cb3601 ("KVM: PPC: Book3S HV: Add fast real-mode H_RANDOM implementation.")
    Cc: stable@vger.kernel.org # v4.1+
    Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20220727143219.2684192-1-mpe@ellerman.id.au
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/platforms/powernv/rng.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/arch/powerpc/platforms/powernv/rng.c
    +++ b/arch/powerpc/platforms/powernv/rng.c
    @@ -63,6 +63,8 @@ int powernv_get_random_real_mode(unsigne
    struct powernv_rng *rng;

    rng = raw_cpu_read(powernv_rng);
    + if (!rng)
    + return 0;

    *v = rng_whiten(rng, __raw_rm_readq(rng->regs_real));


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